It's always tough to talk conclusively about modified engines, but broadly speaking if the thing idles cool but runs hot either the thermostat isn't fully opening (bypassing too much heat to the engine) or the radiator isn't up to the task. While there are some instances of cars that have underdesigned cooling systems (Focus RS!) I've not really seen that happen too much with trucks operating as designed. Manufacturers have testing for this. If you know the cooling system is in good shape (pump, thermostat, radiator) I'd assume the radiator is insufficient. I've seen a lot of vehicles which have clogged up radiators not working so great... It might be worth scanning it with an IR gun to be sure it's equally hot.

I can't imagine adding a water cooled turbo means anything here... A bunch of cars went from non- to water-cooled turbos in the '80s and nobody changed a cooling system. Hell, people add turbos and don't change the cooling system. I don't know... But I don't think.

Please post the specific engine applications of the two vehicles you describe... the 450hp Corvette vs. the 200hp Buick.

It is my contention from the research and development I have conducted on the HDS Model 001 that the thermostat and the housing surrounding it is a pinch point in the cooling system of any given engine. This means that if you can increase the size of the pinch point you can potentially increase the cooling system's capacity to cool. A larger radiator is not simply the only means to increase a cooling system's capacity to cool; it may be the primary way to increase capacity, but it is not the only way.

However, the rest of the cooling system must also be able to shed the heat generated from the engine. Typically, in CRD engines there are three likely culprits that limit the cooling system's capacity to cool the engine; the failure or malfunction of any of the following three will result in a steady rise in engine temperatures past what is considered normal when the engine is working hard. Those three culprits are...

1) Failure of the fan clutch.

2) A clogged radiator, (from the inside OR the outside with dirt, debris or insects).

3) A failed or worn out water pump.

CHECK YOUR FACTS.... DIESEL ENGINES ARE THE EXACT OPPOSITE OF GASOLINE ENGINES IN REGARDS TO RUNNING LEAN AND RUNNING RICH. RUNNING LEAN WILL MAKE A GASOLINE ENGINE RUN HOTTER WHILE RUNNING RICH WILL MAKE IT COOLER. RUNNING LEAN WILL MAKE A DIESEL ENGINE RUN COOLER WHILE RUNNING RICH WILL MAKE IT RUN HOTTER.

For the record, not all of my threads are available on LOSTJEEPS due to the fact that the I have had clashes with the administration here.

Temperatures in internal combustion engines are controlled by two factors in any given thermostat... the opening temperature, and the total flow capacity of the valve/housing itself in the rare occasion when the valve is fully stroked open. The opening temperature of the valve maintains the minimum temperature the engine operates at, while the total flow capacity is the upper limit to what the cooling system is capable of cooling at that pinch point, with acknowledgement that there are other components in the cooling system that have upper limits as well. As I posted earlier, there are components you should look at if your engine starts to overheat when it is worked hard.

Look at the fan clutch to see if it is operating correctly, look to see if the radiator is clogged, (either inside or out), and ask yourself if you changed out your coolant pump when you performed a timing belt service. Before doing any of this, however; check to make sure your O.E. temperature sending unit is functioning properly by performing a cross-reference check using an IR temperature gun of known accuracy and shooting the beam to the top of the thermostat. Measure the IR gun reading against a reading from an OBDII reader or through a Torque Pro app on your mobile device.

The Hot Diesel Solutions Model 001 engine thermostat assembly was deliberately made larger so that tighter control is maintained over engine temperatures as there is more stroke capacity in the larger thermostat valve the Model 001 is designed to use to accommodate more extreme driving conditions than the O.E. valve in the O.E. assembly. The larger housing has the capability to flow more coolant than the stock O.E. housing in the unlikely event you would ever stroke the valve fully open. This assumes that all of the rest of your cooling system components are working correctly.

thesameguy is simply incorrect when he states that thermostat valve size is not a factor in cooling system capacity. It is not the ONLY factor, but it is indeed a factor.

I have CRD owners using the hottest valve available for the Model 001 in some very extreme driving conditions, including rock crawling in the Florida Panhandle, towing 5000 lb loads up mountain passes in Idaho, and every day driving and towing in Alice Springs, Australia. Rock steady 203 degree temperatures at all times, until such time in the distant future when the valve inside the Model 001 fails; then go to any auto parts store, cough up $20.00 to replace it and change out the valve in less than an hour.

I will send an e-mail message and set up a time when we can talk to discuss your cooling system problems.

You may also reduce the system capacity - often the thermostat is intentionally sized to help create a pressure differential. Water under pressure carries more heat than water not under pressure, so the thermostat can be part of an integral system of heat carrying & shedding. Similarly, there is the concept of an ideal flow rate when it comes to coolant - too slow and heat transfer is inefficient, too fast and you introduce cavitation, aeration or even erosion. I would *assume* (I know...) that this sort of stuff is accounted for when someone designs a cooling system. But, without math I'm not capable of doing and knowledge of an engine's design I'm not capable of getting, I certainly couldn't say.

If you've got some A/B testing to prove me wrong, I'd love to see that data. I think when I asked before you indicated you didn't have it. There's not much I've ever read suggestion anything other than the radiator's surface area controls temperature ceilings.

[post duped]

_________________
'15: bought '05 w/138k.
'16: HG/Rockers/ARPs/Thermo/H20pump/TbeltKit/ Seals/ Mounts/Kennedy fuel pump.
'17: bought manual Gas donor for its' ARB F/R Airlockers, OME 2.5" lift (gas-rated), JBA UCAs, ARB bumper.
'19: Trans w/Suncoast/Transgo/HDdiscs, new OME CRD-rated lift, electric tri-fan setup, BlackMagics/Centric Premiums, Airbags.

Emailed you, TDFreak. Thanks!

Informative that some "dry" to h2o-cooled turb factory re-designs didn't upgrade the coolant path. Maybe I've been too obsessed with the turbo's impact on temp spikes.

So, Back to the Big Three:
- WATER PUMP: only 4 years/20k since new. I've performed over 70 Soob 2.5 head gasket jobs (including peripherals) and have high confidence that I properly installed the pump (also new HG/TBelt/Rockers/ Int.Valves-guides-springs/ARP Studs/F-R Oil Seals/etc).
Related: I filled CRD with [NAPA's] CAT-spec nitrogen-charged coolant (= anti-cavitation).
- FANS: given new info that fans are essentially irrelevant over 20mph, my 3-fan electric mod (replacing the stock mechanical fan) can't be the problem. Totally stable temps at idle and at no/low-load speeds & conditions. In fact, on Fan-Low in 70f ambient temps, at idle the gauge reads slightly below 12 o'clock (cooler than mech-fan); @ Fan-High more like 11:30.
- RADIATOR: well, no leaks but that doesn't mean proper flow volume. I own an IR temp gun but never zapped the in vs out tubes of rad = unforgiveably dumb. Turbo is removed so can't confirm specs.

If somebody with a temp-gun gets really bored, it would be useful to know the ballpark-correct temps To vs From rad at normal, warm-engine, op-temps. Presumably, a quick read off the surface of the rad's In-Out hoses would suffice.

_________________
'15: bought '05 w/138k.
'16: HG/Rockers/ARPs/Thermo/H20pump/TbeltKit/ Seals/ Mounts/Kennedy fuel pump.
'17: bought manual Gas donor for its' ARB F/R Airlockers, OME 2.5" lift (gas-rated), JBA UCAs, ARB bumper.
'19: Trans w/Suncoast/Transgo/HDdiscs, new OME CRD-rated lift, electric tri-fan setup, BlackMagics/Centric Premiums, Airbags.

Not just in the in & out temps, but check the actual surface of the radiator. What you'll find with clogged radiators is some passages don't flow properly or at all, and there will be hot or (more likely) cold spots reflecting that. I had an F150 once the PO had reported would overheat and I found the entire lower third of the radiator wasn't doing anything. I bought it cheap, fixed it cheap, and sold it for PROFIT!

How do you do Subie head gaskets? In the car or do you pull the motor? I've read pros & cons of both, and always wondered what pros do...

There are many factors to consider when discussing engine cooling designs or problems.
All of these things can and will factor into engine cooling capacity and efficiency:

1. Radiator surface area
2. Radiator cleanliness factor.
This would also include AC condenser and charge air intercooler or anything else in front of the radiator flow stack that could impact air flow through the radiator core.
3. Radiator internal cleanliness factor. Dirty or corroded flues inside the radiator can greatly inhibit its cooling capacity.
4. Water pump flow rate.
Affected by engine RPM's and condition of water pump impeller, design, along with other factors listed below. The water pump is what forces the coolant through passages in the engine to absorb heat. The pump is driven by the timing belt and also forces coolant through the radiator. The water pump can eventually wear out and will need to be replaced.
5. Coolant hose size. To and from the engine to the radiator.
6. Coolant passages size and design in the engine block and head.
7. Coolant passage size in the head gasket.
These passages can impact the amount of coolant flow passing from the engine block into the head. Some companies actually call them steam ports.
8. Type of coolant.
Some antifreeze coolant formulas or chemical composition have different and / or better thermal adiabatic heat absorption and desorption characteristics.
9. Radiator internal coolant flow rate.
Coolant flowing to slow through a radiator can cause water pump cavitation. Coolant flow to fast through a radiator does not remain in the radiator flues long enough to give up heat to the air flow passing through the core. (This can happen when a thermostat is gutted.
10. Air flow through the radiator core.
Several factors can affect this including cleanliness factors listed above in no.2. Cooling fan type and fan clutch type and condition. Anything in front of the radiator flow stack that could impede or reduce air flow through the stack. Some believe adding air vents or louvers on top of hood helps increase air flow through the radiator stack.
11. Last but not least, the engines coolant thermostat size and housing size.
The size of the thermostat's housing and the thermostat's full open stroke opening area dictates the amount of coolant flow that can pass from the head to the radiator inlet for thermal cooling. Again, too much flow speed through the thermostat could actually be less efficient as the coolant would pass through the radiator to fast to allow proper heat transfer. Back when we were building race engines, we would always put an orifice plate with a certain size hole in it in place of the thermostat. Running an engine without a thermostat or orifice plate caused overheating issues.

So you can see there are lots of factors that play into engine cooling so it can be hard to single out one specific item and say it is the problem when sometimes you have to step back and look at the big picture.

_________________
Supporting Vendor and Moderator of LOST
05 Jeep Liberty CRD Limited
Ironman Springs/Bilstein/Shocks
Yeti StgIV Hot Tune
Week's BatteryTray
No FCV/EGR
Samcos/ProVent
SunCoast/Transgo
Carter Intank-pmp
2mic.Sec.Fuel Filter
Flowmaster/NO CAT
V6Airbox/noVH
GM11 Bld.fan/HDClutch
IronrockArms/wwdieselMount
98 Dodge Cummins 24 Valve

thesameguy: I placed a call and left a message with the Technical Department of Stant Corporation regarding your concerns about pressure differentials. They should get back to me in a couple of days, but I don't believe that your concerns are an issue; otherwise they would have advised me as such when I consulted them in 2013.

I am quite certain that pressure differentials on both sides of a thermostat valve and their effect on cooling system efficiency may only be a concern with old design cooling systems that are open to the atmosphere. Modern cooling systems are pressurized; meaning the entire system is pressurized on both sides of the thermostat to the same degree as it must as defined by Pascal's Law; the principle of transmission of fluid-pressure.

https://en.wikipedia.org/wiki/Pascal%27s_law

What this ultimately means is that the pressure in the cooling system is the same everywhere in the cooling system and the cooling efficiencies derived from the coolant being under pressure are the same no matter the size of the valve. Any extra pressure on one side of the thermostat that could possibly be generated by having a smaller thermostat valve is instantly transferred to the coolant in the rest of the cooling system as per Pascal's Law.

Remember also that a thermostat valve is self regulating; opening and closing according to the thermal signals it receives from the coolant. A larger thermostat valve will simply open a smaller amount than a smaller thermostat valve in the same cooling system under the exact same operational conditions. This would have the effect of keeping the ideal flow rate the same or almost exactly the same and alleviate the concerns you would have regarding the coolant moving too slow or too fast.

Where a larger thermostat valve, (with the appropriately sized larger thermostat housing to accommodate that larger valve), becomes an advantage is when the engine is working especially hard and the cooling demands of the engine outstrip the ability of the O.E. housing to flow the coolant necessary to keep the engine cool. Admittedly, this would be extreme driving - likely towing heavy in very hot weather - and other components of the cooling system would likely need to be upgraded.

One simple upgrade that has been discussed that would be relatively easy to do would be to louvre the hood in the entire area adjacent to the trailing edge of the hood close to the windshield to allow hot air to escape more easily from the engine compartment.

Every diesel truck I've driven, even while unloaded, needed a cooling fan to keep the engine cool at highway speeds.
Flat road, 90F ambient temp, and with the AC-on, you can hear the fan clutch engage.
If the fan clutch never engaged then I might agree with you. But clearly, the fan is required.
Now, add a load and climb a hill. That fan clutch will be engaged the whole way up.

However, I do agree that the CRD radiator is undersized.
It came from the factory with two fans.
At idle, the engine driven fan doesn't move enough air. Especially with the AC on.
This is why the electric fan turns on when you turn the AC on.
At best, the factory cooling system is good for driving to the mall. Not for hauling a load up a hill.

_________________
U.S. Army Retired

I appreciate your thought, but that cannot be true. While we *think* of a cooling system as a uniform pressure, what we're actually thinking of is the *average* pressure, which is usually measured at the point of the cap. If the cooling system was actually of uniform pressure, the water pump wouldn't work. The only way the pump can work is via a pressure differential. The most extreme example is usually at the inlet (low) and outlet (high) ports of the pump, but modern engines are a maze of carefully sized passages and orifices designed to produce specific results. Messing with portions of the maze will change how it works. Maybe for the better, maybe for the worse. Without some pretty exact knowledge of what the designers had in mind, you can't anticipate the full effect of changes.

This is true, but please keep in mind that this is an example of what they used to do with a racing engine.... the driving conditions in racing are unique and are much different than towing heavy in hot weather. The extreme speed and the cooling effect that high velocity air has over a radiator is a factor, the fact that a diesel engine produces heat in a different way than a gasoline engine is a factor, and the unique cooling system challenges of racing engines are a factor.

I agree; the thermostats in racing engines were initially removed because it was thought removing the restrictive valve would bring engine temperatures down; the reality was that it did not and that engine operating temperatures actually went up. The removal of the thermostat valve sped up the coolant flow so much that there was not adequate time to absorb heat from the engine or shed it through the radiator. However, removal of an entire thermostat valve is not the same as substituting a larger thermostat valve in a larger housing... there is still a restriction with the larger valve that closes down completely when the engine is not even up to the opening temperature of the valve, plus you have the self-regulating action of any thermostat valve to stroke open and closed according to the thermal demands of the coolant.

Even when fully stroked open a larger thermostat valve will not flow the same amount of coolant that a cooling system with no thermostat will. The coolant flow rate will never get so high that you will encounter the problems seen in the racing engine with no thermostat valve scenario. The proof with regards to my choice for the larger Hemi thermostat valve in the Model 001 is in customers who have used their Model 001 modified CRD engines in some pretty extreme conditions and have reported back to me that they have rock-steady engine operating temperatures.

I can't speak to diesel trucks you've driven, but the math is undeniable. There is no vehicle mounted fan that can out-flow a vehicle at freeway speed.

I think what you may be observing is the fact that mechanical fans aren't very smart, and they respond only to water pump or ambient air temps, so when those temps climb the fan engages... there's no way to prevent that. It's not necessarily commentary on it being needed or not, it's a limitation of the technology. That's why you often see fuel economy improvements with electric fans - because not only do that not spin unnecessarily due to drag but they also tend to not engage extraneously.

Purely anecdotally, I have not had the same experience of you. I've owned two diesel Suburbans and neither acted as you described. On one, an '84 non-turbo, I would often be reduced to a crawl going up the Sierras... and at 35mph with the pedal floored the fan would eventually kick in. But flat ground? Never. I have the same experience in my motorhome. Admittedly, it's gas-powered, but on flat land the fan never runs. It's only on big pulls at low speed. (And believe me - you KNOW when the fan is running... it's 3' across and right underneath the steering wheel)

There really is no too fast or too slow through a heat exchanger. Whats more relevant is the media through which heat is exchanged. (water and air)
If coolant moves slowly through the engine, it moves equally slow through the radiator.
Likewise, fast through engine, fast through radiator.
Whats most important is adequate surface area to transfer heat. Both inside and out.

The cooling system will function best with some restriction at the outlet to the radiator. (thermostat)
This will help prevent steam pockets from forming, even when the cooling system is already pressurized.
Also, by giving the water pump something to push against, cavitation at the water pump inlet is reduced.

_________________
U.S. Army Retired

thesameguy:

I believe you are conflating a pressure pump, (A.K.A. a positive displacement pump) with a volume pump. Pressure pumps may work on a pressure differential, but engine cooling system pumps are volume pumps, Sir. Here is what I found through GOOGLE when I typed the phrase "Is a cooling system water pump a volume pump or a pressure pump?"

"Water pumps are not positive displacement pumps. The water pump is a centrifugal pump that can move a large volume of coolant without increasing the pressure of the coolant. The pump pulls coolant in at the center of the impeller."

Pascal's Law is not under debate here and there is no such thing as "average" pressure reading in any volume of in-compressible fluid in a confined area; to say there is an average pressure connotes that there are high and low pressure readings throughout the confined area and this is impossible. I can put a pressure gauge on any two points of the cooling system at any time and any temperature and get the exact same pressure.

This assumes that temperature is always uniform throughout the entire engine.
But hot spots absolutely do happen.

_________________
U.S. Army Retired

Your math may be accurate, but your application of that math to real world situations are not taking into account the variables that many - not all - vehicles encounter.

One of those variables is a rather common problem, especially in modern vehicles with very crowded engine bays. In many cases, (perhaps not yours), heat is built up in a cooling system despite the fact that a lot of air is blowing on the radiator because that outside air can not properly go though the radiator due to higher ambient pressures of very warm air in the engine compartment that can not properly escape... the engine operating temperatures will go up as a result and the fans will kick in.

If this problem is apparent in any given application a cooling system engineer needs to be able to evacuate most of the hot air trapped in an engine compartment even at highway speeds. A possible solution to this problem is the installation of rearward facing ducts or louvers to draw the hot engine compartment air out. A cooling system fan will kick in less if the hood is louvered in the appropriate areas to allow the higher pressure warm air to escape and allow more cooler air into the engine compartment.

I have also encountered the fan kicking in is as a trucker hauling loads and running empty, just like Flash7210. The fans on commercial diesel engines are actuated typically by electro-magnetic fan clutches; they are of extreme quality and are operated using proper temperature sending units so they are accurate in their engagement and disengagement.

I am posting about pressure, not heat. Any extra static pressure created by that heat is instantly distributed throughout the coolant in the entire system as per Pascal's Law.

The concern as posted by thesameguy is pressure differentials created by the water pump. As I just posted earlier, a water pump is a volume pump and does not create pressure in a confined space.

This website put it into words better than I could:
https://bangshift.com/general-news/tech-stories/water-pump-101-whats-really-going-water-inside-engine/

_________________
U.S. Army Retired

I agree with you here.
Aerodynamics will effect how air flows over, around, and through the radiator.
As does pressure under the hood.

_________________
U.S. Army Retired