Inline thermostat issues

WWDiesel · **Posted:** Fri Nov 20, 2020 10:25 pm

I am going to try and be diplomatic here. :wink:

If you choose to install an inline thermostat, so be it, it is your engine and you can do whatever you want to your vehicle, we don't have to pay for any repairs due to making modifications that might cause problems down the road.

This forum is all about helping people and advising them to not make costly mistakes on these unique engines that can cause problems and eventual failures of some kind in the long run.
Forum members do try and explain the science behind certain things when possible, or simply share their own unique personal knowledge, experiences, and sometimes expensive failures when certain modifications simply did not work out as planned go expensively sour. Based on forum members / owners feedback and experiences, it is impossible to recommend installing an inline thermostat. Please do your own homework by searching and reading the warning posts on this forum by some members before you make your own decision, it might possibly save you from a very costly mistake based on their experiences.
Just because it sounds good does not always make it a great idea. The elephant hose mode on the CCV comes to mind, it was a good idea at first, but time proved it out to possibly cause some costly problems in the long run. Most have now abandoned it and installed a ProVent.
We certainly don't make this stuff up, facts do speak for themself, if you choose to ignore costly experience and warnings of others, it may have consequences.

:5SHOTS:

TURBO-DIESEL-FREAK · **Joined:** Sat Apr 17, 2010 3:29 pm **Posts:** 1167

jeepsterkj wrote:

OK guys, here is my experience on using the "Renault 5 hack". The OEM stat on my 2.8 CRD KJ was stuck wide open, and the temperature gauge would still be on cold even after driving for 10 miles at 60mph on a motorway! Clearly this would have to be sorted out ASAP.
I am currently out of work, and can only afford to spend tiny amounts of money on maintaining my KJ, so replacing the OEM stat would have been way too expensive...I heard about the Renault 5 Hack on a KJ group on Facebook, and it seemed to be the solution I needed, so I did some research of Renault 5 Thermostats and I ended up buying the cheapest one I could find...An Intermotor 75035, that opens at 86.5'C (187.7'F), and it cost me just £4.24 on ebay. I already had another Stainless steel 50mm hose clamp so I was ready to install it as soon at arrived.
I figured some lube would be handy to help push it into the hose...So I used a smear of Vaseline on in the inside of the hose. There is a round lip at the bottom of the large end of the stat, and you can push it in that far easily, then the lip stops it going any further. So I had to lever the end of the hose out a bit with a flathead screwdriver to get the lip inside the hose...You can then push about half of the stat into the hose but to avoid damaging the three fingers holding the smaller copper end to the larger end, I then used a Vaseline lubricated deep 27mm socket to push it right in, till the end of the copper bit was flush with the end of the hose.
Then I used my 50mm hose clamp to clamp the large end of the stat inside the hose in place, then fitted the hose back onto the OEM housing and tightened up the original hose clamp...The whole operation only took 2-3 minutes, and I could have done it quicker than that but I had to keep going indoors to get more tools out.

Results: After running the engine on tick over for about 3-4 minutes the temperature gauge started to move slowly upwards and after about 5-6 minutes it would reach a fraction under half way, and stay there. Driving down the road warms it up even quicker.
The temperature gauge has not gone over half way (normal operating temperature), even after driving 6-7 miles, so this a very stable mod too.
I should add that a few weeks before doing the Renault 5 hack, I swapped my OEM 5 blade metal fan for a used 11 blade plastic fan off the 3.7 V6, but with the original 2.8 CRD viscous clutch bolted onto it...The plastic fan blows more air than the metal one, it's 500g lighter, and it's quieter too, so it definitely an upgrade. KJ 2.8 CRD exported to Australia got the same fan as stock, presumably because it's better airflow helps with the hot summers there.
The 7 blade plastic fan off the KK would have been my first choice, as it would absorb less power than the 11 blade, giving better fuel economy, but it was too expensive for me, so the 11 blade had to do.
If you live somewhere with a very warm average climate, and you still have the stock steel fan, then it's possible the temp gauge will go over 1/2 with this mod, but I can't confirm that as it's Autumnal weather here at the moment, and starting to get colder as the weeks go by. Summary:
Pros: Works perfectly, extremely quick to install, very simple to install and very cheap to do. (over 3x cheaper than the cheapest aftermarket alternative to the OEM thermostat, and over 100 times cheaper than some alternatives being offered!)
Cons: None (so far).
There are several KJ CRD owners that have been running the Renault 5 hack for over 6 years, and they have clocked up over 100,000 miles with no issues whatsoever, so I for one have no problems recommending this mod.
I put this diagram together to better show the mod to those interested:

jeepsterjk:

Clearly you do not understand the long term implications of using an inline thermostat valve, and you also do not understand the gravity of your own diagrams.

Our concerns have nothing to do with whether or not your engine will warm up adequately, but rather with other unintended consequences. We do know that the inline thermostat modification will indeed warm up your engine and everything will seem fine, but you are slowly warping your head with this modification.

Your own diagrams show that the cooling system bypass circuit is permanently shut down when you leave a failed O.E. thermostat assembly in place, as the CRD engine has a valve controlled cooling system bypass circuit. This essentially relegates your engine's cooling system to a 1 circuit cooling system; the one flowing through your radiator. If you stick another thermostat anywhere in the radiator circuit in conjunction with a failed O.E. thermostat assembly, any time that additional thermostat is closed down you do not have adequate coolant flowing through your engine. Hot spots will form - starting right at the exhaust ports - and your head will warp over time.

There is also another problem with the "Renault 5 Hack"... the thermostat valve designed for the Renault 5 engine is sized for that engine, the biggest version of which is 1.4L. Do you think that maybe, just maybe it might be a tad too small to flow enough coolant for an engine that is twice the displacement and more than twice the power and weight? Try towing with any CRD that has the Renault 5 Hack, and you are looking at a real overheat situation. Here is a link to the entire history of the Renault 5 and the engines used in it...

https://en.wikipedia.org/wiki/Renault_5

Here is a link to the hottest versions of the Renault 5; the Renault 5 Turbo. Even this engine does not match the power output of the V.M. Motori R428 engine that powers the Liberty CRD. It is also half of the displacement and less than half of the weight of the R428. Hauling around a car that NOBODY uses to tow with that is half the weight of a KJ Liberty, there is absolutely no chance that engine will EVER create as much heat as the R428.

https://en.wikipedia.org/wiki/Renault_5_Turbo

The only exception would be if the Renault 5 Turbo engine was built into a full-blown race engine, but at that point none of the stock cooling system components would be used...

https://rallygroupbshrine.org/the-group ... t-5-turbo/

What seems clear to me is that if you are out of work and can not even afford to replace the O.E. thermostat with another one, then consider parking your CRD until you can put proper parts in it. Find another cheaper vehicle to run around in until you get back on your feet. This is not a vehicle to be making cheap upgrades on; it will end up biting you on the booty.

PZKW108 · **Joined:** Sun Apr 06, 2014 5:23 pm **Posts:** 461

jeepsterkj wrote:

OK guys, here is my experience on using the "Renault 5 hack". The OEM stat on my 2.8 CRD KJ was stuck wide open, and the temperature gauge would still be on cold even after driving for 10 miles at 60mph on a motorway! Clearly this would have to be sorted out ASAP.
I am currently out of work, and can only afford to spend tiny amounts of money on maintaining my KJ, so replacing the OEM stat would have been way too expensive...I heard about the Renault 5 Hack on a KJ group on Facebook, and it seemed to be the solution I needed, so I did some research of Renault 5 Thermostats and I ended up buying the cheapest one I could find...An Intermotor 75035, that opens at 86.5'C (187.7'F), and it cost me just £4.24 on ebay. I already had another Stainless steel 50mm hose clamp so I was ready to install it as soon at arrived.
I figured some lube would be handy to help push it into the hose...So I used a smear of Vaseline on in the inside of the hose. There is a round lip at the bottom of the large end of the stat, and you can push it in that far easily, then the lip stops it going any further. So I had to lever the end of the hose out a bit with a flathead screwdriver to get the lip inside the hose...You can then push about half of the stat into the hose but to avoid damaging the three fingers holding the smaller copper end to the larger end, I then used a Vaseline lubricated deep 27mm socket to push it right in, till the end of the copper bit was flush with the end of the hose.
Then I used my 50mm hose clamp to clamp the large end of the stat inside the hose in place, then fitted the hose back onto the OEM housing and tightened up the original hose clamp...The whole operation only took 2-3 minutes, and I could have done it quicker than that but I had to keep going indoors to get more tools out.

Results: After running the engine on tick over for about 3-4 minutes the temperature gauge started to move slowly upwards and after about 5-6 minutes it would reach a fraction under half way, and stay there. Driving down the road warms it up even quicker.
The temperature gauge has not gone over half way (normal operating temperature), even after driving 6-7 miles, so this a very stable mod too.
I should add that a few weeks before doing the Renault 5 hack, I swapped my OEM 5 blade metal fan for a used 11 blade plastic fan off the 3.7 V6, but with the original 2.8 CRD viscous clutch bolted onto it...The plastic fan blows more air than the metal one, it's 500g lighter, and it's quieter too, so it definitely an upgrade. KJ 2.8 CRD exported to Australia got the same fan as stock, presumably because it's better airflow helps with the hot summers there.
The 7 blade plastic fan off the KK would have been my first choice, as it would absorb less power than the 11 blade, giving better fuel economy, but it was too expensive for me, so the 11 blade had to do.
If you live somewhere with a very warm average climate, and you still have the stock steel fan, then it's possible the temp gauge will go over 1/2 with this mod, but I can't confirm that as it's Autumnal weather here at the moment, and starting to get colder as the weeks go by. Summary:
Pros: Works perfectly, extremely quick to install, very simple to install and very cheap to do. (over 3x cheaper than the cheapest aftermarket alternative to the OEM thermostat, and over 100 times cheaper than some alternatives being offered!)
Cons: None (so far).
There are several KJ CRD owners that have been running the Renault 5 hack for over 6 years, and they have clocked up over 100,000 miles with no issues whatsoever, so I for one have no problems recommending this mod.
I put this diagram together to better show the mod to those interested:

Relying on the OEM temp gauge of the vehicle is a big NO NO, a tad bit bellow top mark is anywhere between 165 and 210. If you think your engine temp is stable because the OEM gauge is not moving, you are wrong.
The number of blades and the material the fan is made of as nothing to do with how much air it will push, it as more to do with the pitch and the shape of the blades. For Geordi and is "theory" :dizzy:

about more blades is more better because that's what submarine are using is also wrong. A military submarine impeller is design to avoid the noise produce by cavitation. It might actually be less efficient than a regular boat....It is also for WATER not air :ALONE:

So jeepsterkj you don't have much to back up your theory about the R5 Stat mod. You might just have been lucky you didn't damage anything yet.

This CRD engine is very high maintenance and very expensive to rebuild. It is also not a low budget vehicle keep that in mind.

The only viable alternative to the OEM Stat housing is the model 001, one of the best engine mod for the CRD !

Jett · **Joined:** Fri Apr 17, 2020 12:07 am **Posts:** 250

There is another alternative to the hds001 and that is this mod, which I’ve implemented and it works beautifully. I would never solve my Jeep stat problem with ghetto French parts like that. But, ymmv.

viewtopic.php?f=5&t=50940#p566488

WWDiesel · **Posted:** Sun Nov 22, 2020 11:43 pm

Jett wrote:

There is another alternative to the hds001 and that is this mod, which I’ve implemented and it works beautifully. I would never solve my Jeep stat problem with ghetto French parts like that. But, ymmv.
viewtopic.php?f=5&t=50940#p566488

Or you can just simply install an OEM thermostat, it is still vastly superior as opposed to stuffing in some inhose hack job!

TURBO-DIESEL-FREAK · **Joined:** Sat Apr 17, 2010 3:29 pm **Posts:** 1167

Jett wrote:

There is another alternative to the hds001 and that is this mod, which I’ve implemented and it works beautifully. I would never solve my Jeep stat problem with ghetto French parts like that. But, ymmv.

viewtopic.php?f=5&t=50940#p566488

Yes... as I have posted earlier on another thread Mark Kapalczynski has made the best modification of a O.E. thermostat assembly that exists. Here is what I posted...

"Mark Kapalczynski is a GREAT GUY, and his thermostat upgrade is the ONLY one I recommend if you can not afford mine. I respect his design of a modified O.E. housing to take the Hyundai Excel thermostat valves because he is respecting the original design of the CRD engine thermostat assembly. He realizes that there were very good reasons why the O.E. thermostat assembly was designed this way and copied the design and function of it merely by modifying the O.E. thermostat housing and making it serviceable.

The problems with his design are all due to the cheap cast housing he was forced to work with. Your statement that it leaks does not surprise me, but that is certainly nothing that Mark could be faulted for.

Mr. Kapalczynski's design is no longer viable because one of the critical parts to make it is so hard to come by. I did some research back in 2013 to find out if I could take over making O.E. thermostat upgrades as Mark indicated that he no longer wanted to do it. I discovered way back then that the KIA Sephia thermostat cap was a discontinued part.... when I factored this sobering reality with the logistical problems of sourcing used O.E. thermostat assemblies I knew it was a no-go for me.

At that point I knew that if I wanted to create a truly superior upgrade serviceable thermostat I had to start with a clean sheet design. The Hot Diesel Solutions Model 001 is the result of my research and development efforts.... it is vastly superior to the throwaway O.E. thermostat assembly in EVERY way, and better than any other alternative solution - including Mark's design - that has been tried so far."

Here is your quote from the other thread when I asked you what 195 degree thermostat you were writing about. You replied "Kapeznpickic mod. Using kia parts etc. lathe work and welding, and leaks, but works great". The fact that the Kapalczynski modified O.E. thermostat housing is prone to leaking should serve as a warning to others considering this modification.... the O.E. cast housing simply does not have enough metal to install more than two 6MM studs to hold everything together in the long run, and I fear that there may be catastrophic failures because of this. The Model 001, on the other hand, has three 8MM stainless steel studs set in a very robust machined housing made from solid blocks of 6061 T6 aluminum; as such it will never leak if it is properly installed.

An additional problem I have with the Kapalczynski mod is that it uses a thermostat from a 1.5L naturally aspirated four cylinder gas engine that makes about 1/2 the power and weighs about 1/2 of a CRD engine. There is little chance that a thermostat sized for such an engine will flow enough coolant for the CRD engine in high demand situations, like towing a heavy load up a hill in the summer. You are likely looking at an overheat situation if you try to tow anything significant with a Kapalczynski mod.

thesameguy · **Joined:** Sat Oct 01, 2016 8:24 pm **Posts:** 652

The size of the thermostat has little to do with its ability to manage heat. A '79 Pinto made 83 horsepower from a carbureted, 2.3l four cylinder. That engine's exact same thermostat is in my 1986 XR4Ti making 300hp on 25 pounds of boost. It's a darling little thing, about an inch in diameter. Zero cooling issues, even in 100 degree weather doing a 0-5000' run at completely irresponsible speeds up the Sierra Nevadas. There are lots of reasons to be skeptical of hacky cooling system modifications, but physically small thermostat is not one of them. Volume of passageways had about sod all to do with anything.... my 400hp CTS-V has "normal" 1 5/8 radiator hoses just like my 140hp Saab.

.

Jett · **Joined:** Fri Apr 17, 2020 12:07 am **Posts:** 250

thesameguy wrote:

The size of the thermostat has little to do with its ability to manage heat. A '79 Pinto made 83 horsepower from a carbureted, 2.3l four cylinder. That engine's exact same thermostat is in my 1986 XR4Ti making 300hp on 25 pounds of boost. It's a darling little thing, about an inch in diameter. Zero cooling issues, even in 100 degree weather doing a 0-5000' run at completely irresponsible speeds up the Sierra Nevadas. There are lots of reasons to be skeptical of hacky cooling system modifications, but physically small thermostat is not one of them. Volume of passageways had about sod all to do with anything.... my 400hp CTS-V has "normal" 1 5/8 radiator hoses just like my 140hp Saab.

.

I agree and I’ve proved it out on my Jeep crd, stage 4 tune, hauling 75mph up a long grade with another liberty on a car trailer. That’s as much as you can throw at it really. Speeds fell slightly, egt’s rose sharply, but the coolant needle was straight up the whole time.

WWDiesel · **Posted:** Tue Nov 24, 2020 12:57 pm

Jett wrote:

I agree and I’ve proved it out on my Jeep crd, stage 4 tune, hauling 75mph up a long grade with another liberty on a car trailer. That’s as much as you can throw at it really. Speeds fell slightly, egt’s rose sharply, but the coolant needle was straight up the whole time.

What was the ambient temperature and relative humidity, they both have a huge influence in the cooling ability of your heat exchanger (radiator)?

Coolant FLOW rate does matter immensely when it comes to cooling system designs. Thermostats, hoses, pipes, radiators, water pumps, etc... are all designed, rated, and matched to engines for optimal ability to remove heat from an engine under full load conditions. Changing the flow rate, either limiting it or increasing it too much can have unwanted effects on cooling ability. Too low of flow will prevent the coolant from removing the heat fast enough from the critical high temperature areas in the head. Too much flow can push the coolant through the radiator too fast and not allow it to exchange (give up) it's absorbed heat properly. Back in my racing days when we were building race engines, we never installed a thermostat, but instead installed a metal orifice in its place to control the flow of the coolant through the radiator at the optimum rate for the wanted cooling effect.

Bottom line, be careful when changing flow rates on cooling systems, they are designed and engineered a certain way for a reason and if you start changing those flow rates either up or down, it can cause problems. :juggle:

Quote:

Flow rate and heat transfer
Heat transfer of coolant flow:
The effect of heat transfer increases as the flow of coolant changes from laminar flow to turbulent flow. For laminar flow, heat can be transferred only by means of heat conduction from layer to layer. However, in turbulent flow, the mass transfer in the radial direction enables the heat to be transferred by both conduction and convection. As a result, the efficiency increases dramatically.
Since the increase of heat transfer will diminish as the coolant flow becomes too turbulent, there is no need to increase the coolant flow rate beyond a certain amount. Otherwise, the small, marginal improvement in heat transfer will be offset by the higher pressure drop across the cooling channels and resident time in the heat exchanger.
It is very important to make sure that the coolant reaches turbulent flow everywhere in the cooling system, too low of a flow rate only produces laminar flow which is very inefficient in a cooling system.

thesameguy · **Joined:** Sat Oct 01, 2016 8:24 pm **Posts:** 652

The cooling system at its core is there to facilitate the transferring of electrons.... initially from hot metal to water, then from water to air. Electrons move VERY fast - much faster than water - and they don't really care where they go so long as it's less exciting than where they are and they are more apt to move when that delta is very big.

When water moves too slowly, the areas in the hottest part get heat soaked, the delta decreases, and that movement of electrons is reduced which is undesirable. But once you get to a flow rate where heat soaking isn't an issue, you can basically move the water as fast as you want with no ill effects as far as heat transfer is concerned.

I would think the boundary for flow rate is really a function of pump size. If the pump moves too quickly, it will induce cavitation which will dramatically reduce heat transfer. The pump's design is such that it moves enough water at low speed to avoid heat soak but never moves too fast that it causes cavitation. Removing a thermostat entirely won't change the pump's speed so there is no risk there.

(This is one of the major advantages of modern electric water pumps (BMW, etc.) - they move only as fast as they have to and no faster, doing exactly what they need to without costing extra energy)

The other consideration of coolant moving too fast is laminar flow, where water forms layers of temperature, hotter on the outside than it is on the inside. The temperature delta between the metal and the water is reduced, so heat transfer is compromised. Most vehicles solve this issue by introducing turbulence via water pump and/or passageway design so that laminar flow is disrupted.

I don't know this 'cause I'm not that smart, but I'd wager older engines weren't so conscientiously designed, and may have done things like used the thermostat to create pressure differentials between engine and radiator (to modify heat carrying & shedding capacity) or be part of that turbulence effect (to improve heat transfer). Lots of improvements have been made to cooling systems - especially in the last 20-30 years as emissions and economy standards have forced everyone to be more efficient. I would expect - but don't know - functions to be a bit more precise and compartmentalized. The thermostat controls flow to the radiator, the water pump creates turbulence, the ratio of upper to lower radiator hose enforces pressure differentials.

As a for instance, my same XR4Ti came from the factory with a partial pressure cooling system, the type of thing you'd find on '60s cars. Well, and a lot of domestic cars in the '80s.

That is, the cooling system only became pressurized after a certain temperature was reached. The problem with that design is local boiling - the overall system temp is low, pressure hasn't been achieved, and water in the hottest spots vaporizes. Heat transfer drops off as a result, and you crack heads. Years ago I converted the system to a full pressure design, where pressure comes up "instantly" and evenly through the system to prevent local boiling. As a result, I've suffered no further head failures.

TL;DR - On a modern vehicle like a CRD Jeep, I would generally trust the engineering that went into it was thoughtful and comprehensive. At the same time, production cars are "one size fits all" so my California CRD that needs to exist in traffic between 30F and 110F may include some concessions to people in Minnesota driving open roads between 0F and 80F. i certainly believe there is room to optimize. I mean... I'm sure Ford didn't anticipate people putting 25 pounds of boost through a Pinto.

But, uh, I do think it's important to look at things like cooling systems as systems and not anticipate you can randomly change doo doo up and get wholly positive results. To that end, I also think it's important to understand how a system works to a high degree before setting out to change it. This coming from a guy whose blown a lot of stuff up over the years.

WWDiesel · **Posted:** Tue Nov 24, 2020 5:13 pm

thesameguy wrote:

To that end, I also think it's important to understand how a system works to a high degree before setting out to change it. This coming from a guy whose blown a lot of stuff up over the years.

Love your writeup, definitely on point. I think we are on the same page?

I certainly believe that stuffing some none OEM object in a top radiator hose like a small thermostat can restrict/lower the total flow rate even to a point where it can change adversely the normal turbulent flow through the head to a laminar flow which can cause the thermal separation as you described and improper heat transfer. Flow rates are just as important if not more important than all other factors due to resident times the coolant is exposed to either the heat source for heat flux absorption or the heat exchanger where it gives up the heat to the cooling air.
Thermal dynamics is a complex science.... :ALONE:

thesameguy · **Joined:** Sat Oct 01, 2016 8:24 pm **Posts:** 652

I really have no idea at all! It's certainly possible that adding that restriction in the URH will encourage hot spots, but it's entirely possible that it's no functional issue whatsoever. The only real way to know is measure flow before and after, or maybe measure cooling system pressure before and after and infer? My only point is that "small thermostat" isn't *inherently* an issue as anyone with an old turboford will begrudgingly tell you. There are people with 500hp SVOs cooling with 1" Motorcraft thermostats. It's just not an issue. I think there is a pretty big window before flow is restricted to the point it's "too slow."

I'm similarly unconvinced that the inline thermostat is any other type of issue either, BUT I don't know how the cooling system works. On cars that I know best - old Fords and Saabs - the "closed thermostat bypass" is ALWAYS open. As you'd expect, this is called an "open bypass system." There's no way to close it off. But it's such a restricted passage that as soon as the the thermostat opens water will strongly favor the radiator path. IF the CRD is designed as that diagram above indicates (called a dual poppet system) where the thermostat actively directs flow to the bypass OR the radatiator, then yeah, that's a big freakin' problem. That would mean a bunch of coolant is basically trapped in the bypass circuit and the engine is effectively uncooled for 15-20 minutes every time the engine is started. That's no good. I'd want to be very sure of that operation! I've got the thermostat that came off my motor and won't be reused.... I guess it wouldn't be tough to yank the thermostat motor out and see if it's a single or dual poppet system.

Edit: This, BTW, is an amazing article:

https://www.coolcatcorp.com/thermostats ... stems.html

I've referenced it frequently!

flash7210 · **Posted:** Tue Nov 24, 2020 9:21 pm

thesameguy wrote:

The cooling system at its core is there to facilitate the transferring of electrons....

No.
Electrons are not being transferred.
If there was a transfer of electrons, that would indicate a chemical reaction. Which is something you dont want happening in your cooling system.

What IS happening is the transfer of thermal energy.
The atoms of coolant/water are hot and excited. To drop to a less excited state, energy must be released or exchanged to a substance that is less hot or has a higher capacity for heat.
The radiator, with its many tubes and increased surface area, is where the heat exchange happens.
Coolant/water flow through those many tubes actually slows down, when compared to flow through the engine, providing sufficient time for heat exchange with the air passing through the radaiator.
Translation: larger radiator with more tubes = better cooling.

Now, there are situations where chemical reaction and electron exchange can happen in the cooling system.

First, a galvanic reaction!
Dissimilar metals, such as aluminum and iron, can cause a chemical reaction when catalyzed by a water/coolant mixture that has become too acidic.
Translation: THIS IS BAD! And will cause massive corrosion.
Not only can it be detected with pH paper but it also produces a small amount of voltage that can be seen with a voltmeter.

Second, minerals in your cooling water.
The minerals dissolved in your tap water or drinking water or spring water are free ions.
Those free ions contribute to the corrosion of iron and other metals.
Just like how ocean water or salted icy roads will cause your frame and body panels to rust.
Rust is a chemical reaction.
Thankfully, automotive coolants are corrosion inhibitors and if you use distilled or de-ionized water corrosion resistance will be improved.

Finally, one more detail about the thermostat in a automotive cooling system.
The thermostat is designed to provide a restriction to coolant flow even when its fully open.
Basically, the water pump needs something to push against, slightly increasing the water pressure in the engine block and head(s). This can help prevent the formation of steam pockets but most importantly prevents cavitation at the water pump impellor.
On race engines, where thermostats aren't always used and only cooling water is allowed, a restrictor disk will be placed in the outlet to the radiator for exactly those reasons.

WWDiesel · **Posted:** Tue Nov 24, 2020 10:47 pm

flash7210 wrote:

Finally, one more detail about the thermostat in a automotive cooling system.
The thermostat is designed to provide a restriction to coolant flow even when its fully open.
Basically, the water pump needs something to push against, slightly increasing the water pressure in the engine block and head(s). This can help prevent the formation of steam pockets but most importantly prevents cavitation at the water pump impellor.
On race engines, where thermostats aren't always used and only cooling water is allowed, a restrictor disk will be placed in the outlet to the radiator for exactly those reasons.

Exactly what I was saying my previous post! And if you install an inhose thermostat that restricts or reduces coolant flow to the point of causing water pump cavitation, it can cause hot spots in the head as the coolant boils off in the high temperature exhaust seat areas due to lack of adequate coolant flow.

And yes, a metal restrictor plate with an orifice in it was what we used in race engines, never had to worry about a thermostat failing.

TURBO-DIESEL-FREAK · **Joined:** Sat Apr 17, 2010 3:29 pm **Posts:** 1167

thesameguy wrote:

The size of the thermostat has little to do with its ability to manage heat. A '79 Pinto made 83 horsepower from a carbureted, 2.3l four cylinder. That engine's exact same thermostat is in my 1986 XR4Ti making 300hp on 25 pounds of boost. It's a darling little thing, about an inch in diameter. Zero cooling issues, even in 100 degree weather doing a 0-5000' run at completely irresponsible speeds up the Sierra Nevadas. There are lots of reasons to be skeptical of hacky cooling system modifications, but physically small thermostat is not one of them. Volume of passageways had about sod all to do with anything.... my 400hp CTS-V has "normal" 1 5/8 radiator hoses just like my 140hp Saab..

I checked Rock Auto, and indeed you are correct that the Pinto engine and the XR4Ti engine have the same thermostat, even though the XR4Ti engine makes over 3 times the amount of power. Two explanations for the reason Ford might be able to get away with this...

1) The Pinto engine clearly appears to be under-tuned for it's displacement/size. It could very well be that this engine makes way more power in other markets around the world and therefore the thermostat is sized larger than it needs to be. It may indeed be the case that the entire engine's architecture was made to handle way more power than what it was tuned for here in North America. Ford, after all, was involved with Cosworth in Europe for many years in racing efforts.

2) While the thermostat is the same on both engines, the water pumps are indeed different part numbers. They look identical, but I openly wonder if the XR4Ti's 2.3L Turbo engine water pump internals were not changed up to flow more coolant, or that it runs on a smaller pulley. If so, that would make a huge difference to the overall cooling system efficiency of each system. I suspect that other components of the XR4Ti are also more robust than that of the Pinto.

Coolant flow does indeed matter, but the particular issues surrounding coolant flow in any given internal combustion engine are application specific. By this I mean that you should not simply take an example of one engine and apply it to another.... there are almost always other factors at play that can make a big difference in the end results. What may work in the Ford Pinto/Mercur XR4Ti example will likely not work in other examples. Remember also that diesel engines have a very different heat curve than gasoline engines... depending upon state of tune, a gasoline engine can overheat simply by idling too fast. A diesel engine has a great deal of trouble heating up significantly until it works hard. There are VERY different animals with very different thermodynamics issues.

This is a very complicated subject with very complex issues and NONE of us - including those armchair engineers who promote the inline thermostat issue - have access to multi-million dollar engine laboratories to sort out these complicated issues. Therefore, the ONLY conclusion I could possibly come up with to resolve the cold-running CRD engine issue when designing the Hot Diesel Solutions Model 001 was to NOT question or disrespect what the engineers of the R428 engine had designed for the cooling system and specifically the thermostat assembly. The HDS Model 001 had to be the same functioning design with all of the same ports and hose barbs. You will not find any problems using the Model 001 because it works exactly the same as the O.E. thermostat assembly.

thesameguy · **Joined:** Sat Oct 01, 2016 8:24 pm **Posts:** 652

flash7210 wrote:

Electrons are not being transferred.

Yes, I know. I was not being literal.

Quote:

Finally, one more detail about the hermostat in a automotive cooling system.
The thermostat is designed to provide a restriction to coolant flow even when its fully open.
Basically, the water pump needs something to push against, slightly increasing the water pressure in the engine block and head(s). This can help prevent the formation of steam pockets but most importantly prevents cavitation at the water pump impellor.
On race engines, where thermostats aren't always used and only cooling water is allowed, a restrictor disk will be placed in the outlet to the radiator for exactly those reasons.

This MAY be true, but it may not be true. Please read my response above. On partial pressure systems where local boiling ("steam pockets") is a problem, systems like a thermostat restriction *could* be used to increase pressure behind the thermostat to reduce that effect before the system fully pressurizes. You can generate the same result by adding other restrictions such a relatively small URH or reduced passage. It's not feasible to infer what the engineer behind the solution was thinking - you can't simply say "the thermostat is the restriction" in a general or universal way. It could be. It could be elsewhere. I'd feel comfortable saying that's how old cars were designed in general, but I wouldn't be so bold as to assume it's true on newer, more comprehensively engineered vehicles.

That said, it probably doesn't matter. Every car since the '90s (and most since the '80s) is a full pressure system - I'm sure the CRD is as well. In a full pressure system, the system becomes uniformly pressurized as soon as there is any measurable heat in the engine. You can watch this happen remarkably quickly on a cooling system pressure gauge. Because the system is fully and quickly pressurized, there is essentially no opportunity for local boiling ("steam pockets"). In the old days, the extra stress of a full pressure system was a risk not worth taking, a cost not worth paying. These days it's s solved problem that improves reliability - full pressure systems are more reliable, short and long term.

My 900 is a full pressure system from the factory, and my XR4Ti was converted with some help from a MK IV VW. I do not run a thermostat in them when they're on race duty. They are full pressure systems and they don't care whether they have a thermostat or not - they behave exactly the same either way. (And yes, this is monitored regularly with sensors and a cooling system pressure gauge - I don't wanna be the guy getting meatballed)

Here is a decent article on partial vs full pressure systems:

https://www.allpar.com/threads/cooling- ... 1085223148

Stant also has an FAQ on the topic but I can't readily find it.

I wouldn't be so bold as to assume anything about the CRD - whether it's a full or partial pressure system, or whether the VM engineers used the thermostat in some sort of secondary way, or anything like that. I don't know, I haven't looked, and I probably couldn't know if I did. But it would be atypical of a modern engine if they did something like this. In my mind, the thing left to discover is whether the thermostat is a single or dual poppet - whether it simply opens & closes the URH path, or whether it actively directs water between the URH and the bypass. For me, that'd be the major issue.

TURBO-DIESEL-FREAK · **Joined:** Sat Apr 17, 2010 3:29 pm **Posts:** 1167

thesameguy:

Your quote:

"I wouldn't be so bold as to assume anything about the CRD - whether it's a full or partial pressure system, or whether the VM engineers used the thermostat in some sort of secondary way, or anything like that. I don't know, I haven't looked, and I probably couldn't know if I did. But it would be atypical of a modern engine if they did something like this. In my mind, the thing left to discover is whether the thermostat is a single or dual poppet - whether it simply opens & closes the URH path, or whether it actively directs water between the URH and the bypass. For me, that'd be the major issue."

Unfortunately, there are a LOT of CRD owners who assume far too much about their rides. It is refreshing to hear from a member like you that makes no assumptions.

If you find an old O.E. thermostat, you can cut it open to discover yourself. I have cut open a couple myself when I was doing research on the Model 001... the valve inside the O.E. thermostat assembly is indeed a dual poppet. This is the primary reason why I chose the Hemi engine thermostat valve as it is also a dual poppet.

I think there may be some kind of mind-meld going on here... the link you posted about CoolCat Express Corp., (https://www.coolcatcorp.com/) is EXACTLY the company I reached out to for additional assurances I wasn't missing something when I was making my arguments against the use of the inline thermostat assembly. Without even explaining the whole situation to the fellow I was speaking to, he mentioned all of the problems that would be exacerbated with the use of an inline thermostat valve in the CRD engine... warped and cracked cylinder heads, head gasket failures and broken exhaust valves.

thesameguy · **Joined:** Sat Oct 01, 2016 8:24 pm **Posts:** 652

TURBO-DIESEL-FREAK wrote:

thesameguy:
If you find an old O.E. thermostat, you can cut it open to discover yourself. I have cut open a couple myself when I was doing research on the Model 001... the valve inside the O.E. thermostat assembly is indeed a dual poppet. This is the primary reason why I chose the Hemi engine thermostat valve as it is also a dual poppet.

I've got one in the garage right now that I won't be reusing, but I've no reason not to take your word for it. If the factory thermostat is a dual poppet, I 100% agree running an inline thermostat would be a very risky proposition. Undesirable restriction or not, defeating the coolant bypass sure seems like it'd be a big deal. Maybe you luck out and the real-world result don't affect you during your ownership, but it's not something I'd be willing to bet my cylinder head on!

WWDiesel · **Posted:** Thu Nov 26, 2020 1:43 pm

thesameguy wrote:

I've got one in the garage right now that I won't be reusing, but I've no reason not to take your word for it. If the factory thermostat is a dual poppet, I 100% agree running an inline thermostat would be a very risky proposition. Undesirable restriction or not, defeating the coolant bypass sure seems like it'd be a big deal. Maybe you luck out and the real-world result don't affect you during your ownership, but it's not something I'd be willing to bet my cylinder head on!

Hopefully these drawings will help show the "guts" of the Jeep OEM thermostat and how it was designed to function normally.
It definitely is a duel valve thermostat! As the bypass valve closes off, the main valve opens to permit flow to the radiator.

TURBO-DIESEL-FREAK · **Joined:** Sat Apr 17, 2010 3:29 pm **Posts:** 1167

thesameguy wrote:

TURBO-DIESEL-FREAK wrote:

thesameguy:
If you find an old O.E. thermostat, you can cut it open to discover yourself. I have cut open a couple myself when I was doing research on the Model 001... the valve inside the O.E. thermostat assembly is indeed a dual poppet. This is the primary reason why I chose the Hemi engine thermostat valve as it is also a dual poppet.

I've got one in the garage right now that I won't be reusing, but I've no reason not to take your word for it. If the factory thermostat is a dual poppet, I 100% agree running an inline thermostat would be a very risky proposition. Undesirable restriction or not, defeating the coolant bypass sure seems like it'd be a big deal. Maybe you luck out and the real-world result don't affect you during your ownership, but it's not something I'd be willing to bet my cylinder head on!

Just for poops and giggles... cut one open. I do not want you to take my word for it, and perhaps you will provide some more insight into this design.

Inline thermostat issues

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