Inline thermostat issues

papaindigo · **Posted:** Tue Aug 09, 2011 8:36 am

I'll let arengant and others who have done the inline install weigh in but my $0.02. The OEM tstat is a sealed unit that diverts coolant flow in different directions as the engine warms up. The typical failure mode for that tstat is an "open" mode; according to kap's research (viewtopic.php?f=5&t=50940) the spring gets weak around 50k miles and the tstat opens too early in the warm up cycle such that the engine never reaches full operating temp. The inline tstat mode essentially works around that failure mode by preventing early coolant flow to the radiator (due to early opening of the OEM tstat) until the coolant temp is high enough to open the inline tstat (hence my comments about the need for a hole in the skirt of the inline tstat to allow venting some flow in that direction to avoid a temp spike after initial startup - NOTE this venting probably is why arengant notes a slight increase in the warm up time as if the OEM tstat was working properly there would be no flow in this direction). With the skirt hole drilled the inline seems to work fine. As far as I know there is no way to "gut" the OEM tstat housing other than kap's mode and if you go that far there is no need for an inline.

IMHO your temp spike going uphill is more likely related to the common bad mechanical fan clutch. There is a ton of chat on the forum about this (ex. search.php?keywords=hayden&terms=all&author=&fid[]=5&sc=1&sf=all&sk=t&sd=d&sr=posts&st=0&ch=300&t=0&submit=Search). Short version is the OEM fan clutch is weak and even when functioning properly opens late in the temp rise curve (ca. 200f air temp) so that the coolant temp may spike after the mechanical fan cuts in. There are instructions in the FSM on how to test to fan clutch for function (I'd add to those instructions advice to use a infrared termostat, available from Amazon or possibly an AutoZone type loan to check the tstat housing for actual temp as some factory temp gauges were set incorrectly see http://www.greendieselengineering.com/f ... st/19.page). If that's your problem the Hayden fan clutch is an inexpensive fix (part cost ca. $60) as this is a much better clutch which kicks in at ca. 170f (e.g. much earlier in the heat rise curve).

arengant · **Posted:** Tue Aug 09, 2011 1:01 pm

I agree 100% with papaindigo on all account. If you are intermitent overheating, start with Hayden clutch fan.

If you are NOT getting warm enough (this winter) either do the OEM thermostat (100 bucks) or inline (50)

William Waddy · **Joined:** Mon May 09, 2011 4:16 pm **Posts:** 56

Thanks for info on fan, i will check it out. The only thing i question about fan being problem is that temp spikes are occuring at 70+ mph. Shouldn't there be sufficient natural air flow at those speeds even if fan was not working properly?

arengant · **Posted:** Wed Aug 10, 2011 9:42 am

William Waddy wrote:

Thanks for info on fan, i will check it out. The only thing i question about fan being problem is that temp spikes are occuring at 70+ mph. Shouldn't there be sufficient natural air flow at those speeds even if fan was not working properly?

Going uphill?

Have you read through this?

viewtopic.php?f=5&t=60943

William Waddy · **Joined:** Mon May 09, 2011 4:16 pm **Posts:** 56

Thanks for the link. I now have a whole bunch of things to check. The overheating also makes more sense now. The 33 inch tires are putting more stress on the drivetrain, even with the 4.56 gearing, and i have not had an alignment done yet since the jba lift and other mods. Highway noise is also much greater than expected, which also points to more drivetrain friction. The hayden mod also sounds worthwhile. Thanks again for all the experience and insight on this forum.

arengant · **Posted:** Thu Dec 01, 2011 11:47 pm

Well, sadly, I am going to now recommend 3/32 for the bypass hole. 1/8 is too big for any ambient temps below 35. It takes a while to reach operating temps now, and the last few days I actually never made it past the 1/4 tic during my 8 mile commute (20 mins) going no more than 35. Cabin heat is fine, but I bet my MPG is just as bad as before the stat.

Sigh

racertracer · **Posted:** Mon Dec 05, 2011 5:00 am

When I swapped out my failed thermostat with a new OEM one, it didn't make a bit of difference with MPG.

My Miles Per Gallon didn't increase.

crhannay · **Joined:** Sun Nov 25, 2012 5:06 pm **Posts:** 2

How does a 1 1/2" inline thermostat work in a 2" hose?

amslube · **Posted:** Mon Nov 26, 2012 5:28 pm

I did the inline t-stat about 2 months ago and drilled the 1/8" hole in the flange. Temp. ran normal but when the weather cooled in October it took much longer to come up to temperature. Also going down long grades the temp would drop. I removed the t-stat and plugged the 1/8" hole with a pop rivet and reinstalled. Temp comes up much quicker to normal even in 20* temps and stays there. Never noticed a temperature spike or any rise above normal needle position.

arengant · **Posted:** Tue Nov 27, 2012 12:10 am

crhannay wrote:

How does a 1 1/2" inline thermostat work in a 2" hose?

It's 2" OD hose....

I bought a new upper radiator hose and a new OEM Tstat. Even though I am in Hawaii now where there is no need to, I devided to because I overheated slightly this past August in 100 degree weather traveling across country fully loaded. Tried to save a few bucks and almost caused massive damage :oops:

CATCRD · **Posted:** Tue Nov 27, 2012 12:41 am

amslube wrote:

I did the inline t-stat about 2 months ago and drilled the 1/8" hole in the flange. Temp. ran normal but when the weather cooled in October it took much longer to come up to temperature. Also going down long grades the temp would drop. I removed the t-stat and plugged the 1/8" hole with a pop rivet and reinstalled. Temp comes up much quicker to normal even in 20* temps and stays there. Never noticed a temperature spike or any rise above normal needle position.

IMO 1/8"' is too big. I installed one undrilled into one of my CRDs, and drilled a 1/32" hole in the one for the other jeep. The second takes a mile or two longer to warm up and does cool off a bit at idle. No temp spikes experienced yet with either one.

flash7210 · **Posted:** Fri Nov 30, 2012 8:54 am

My inline t-stat is working great.
I drilled two 1/16 holes in it, about 180 deg apart.
Worked great all summer and now that it is getting cold the temp comes up to normal like it should.
It takes about 10 min of driving to get it up to temp.
No change in fuel mileage though.

SC RIGGR · **Posted:** Fri Nov 30, 2012 10:39 am

I have now had my inline Stant about a year. We noticed about 2-3 mpg increase and no spikes. Try to make sure the case is agaisnt the metal in the water neck. I started the inline in the hose and used the neck itself to seat it, before I tightened the new clamp. Also the stant has a small hole so I did not drill.

jeepsterkj · **Joined:** Mon Jun 11, 2018 7:38 am **Posts:** 52

crhannay wrote:

How does a 1 1/2" inline thermostat work in a 2" hose?

The "inline" is a Renault 5 thermostat. There are two types available, which open at different temperatures...I only know the Intermotor part numbers for them, so if you buy other brands you will have to research equivalents. There is the Intermotor 75007, which opens at 83'C (181.4'F) or the Intermotor 75035, which opens at 86.5'C (188'F). I bought the 75035 as it was the cheaper of the two (only £4.24 on ebay).
They both have a max outer diameter of 43.5mm (~1 3/16"), but that is the diameter of the rounded lip at the base of the barrel, which holds the top barrel section onto the base "fingers" that taper down to the smaller copper section at the base...The barrel itself is slightly smaller than the lip...In fact it's a perfect sliding fit inside the radiator hose, so when you push it in, it only slides in as far as the lip, then you have to lever the hose out with a couple of screwdrivers to get the lip inside the hose before you can continue pushing it in.
I used Vaseline to lubricate the inside of the hose first. Once you can no longer push on the barrel by hand you need to use a deep 27mm socket, to push it in...But you still have to lubricate the socket with some Vaseline or you won't get it out again, as mine was a perfect fit inside the hose.
The bottom of the copper section should be flush with the end of the hose, then you add your Jubilee clip/hose clamp over where the barrel is inside the hose (you can feel where the lip is) to secure the new thermostat in place. and secure the hose back onto the Thermostat housing. Mine used to stay on cold even after 10 miles of driving!
With the new Renault 5 thermostat installed it reached 1/4 in a few minutes while stationary and after a 2 minute drive it reached just under half way and stayed there. If you fit one that opens at a higher temperature, like the OP did, then you will get a higher than normal reading on the temp gauge...And indeed, the OP was using one that opened at 195'F (90.6'C), so he was simply using the wrong thermostat...There is no need to drill the new thermostat at all, as long as you fit the right one.

flash7210 · **Posted:** Thu Nov 05, 2020 9:34 am

An old thread brought back from the dead :shock:

jeepsterkj wrote:

The "inline" is a Renault 5 thermostat...

I hate to be the one to completely invalidate your detailed and well worded post, but the inline thermostat is no longer a recommended solution.

Dont do it!

I've been there, done that, and cracked a head.
And I'm not the only one that its happened to.

If any of the forum moderators read this, I recommend that this thread be locked.

SC RIGGR · **Posted:** Thu Nov 05, 2020 10:34 am

Hey Flash, I see you list a modified Factory thermostat in your mods. Is it a Kapernick design? If you are advising us against inline, please give an alternative. TIA

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

SC RIGGR wrote:

Hey Flash, I see you list a modified Factory thermostat in your mods. Is it a Kapernick design? If you are advising us against inline, please give an alternative. TIA

Yes, either the kapernick (not the right name but yeah) or the hds001 replacement housing are the only two solutions to this problem. I’m cheap so I did the kapernick version and it works perfectly, but it’s a fairly involved mod that requires some specific raw materials and a lathe.

WWDiesel · **Posted:** Thu Nov 05, 2020 2:13 pm

What I posted in response to the "in-hose" thermostat thread on FB:
When will people ever learn to stop doing this; it is simply not worth the risks and possible expensive consequences.

Quote:

Just a friendly warning, some running the in-hose thermostat have reported experiencing a blown head gasket and a few worse case have experienced a cracked head after installing the inhose thermostat. Simply not worth the possible very expensive risk in my opinion.
The original factory design coolant bypass circuit allows for the very important minimum flow through the head during the critical warm up period to prevent any HOT spots until the engine warms to normal operating temperature. As this happens the OEM thermostat slowly closes off the bypass flow circuit as it at the same time opens up exponentially at the same rate to allow flow to the radiator so there is always a minimum flow of coolant through the aluminum head to prevent any hot spots.
But if you think it is a good idea, repairs are on your dime!

More reason than ever to install a "proper" functioning thermostat like an OEM unit, HDS, or modified OEM since all will have a proper functioning bypass circuit that allows continuous flow of coolant through the head at all times.
But as I stated before, it's your vehicle and you are your own warranty provider and repairs and very expensive parts like a new head are on your dime, so do as you please. Advice is free, choosing to disregard what others are freely telling you from past learned experiences can have very expensive consequences....

If you have a "failed" OEM thermostat, they fail in the full open position with the bypass valve closed. So if you insert (install) an in-hose thermostat in the top radiator hose, you are completely stopping all coolant flow through the engine/head until the inhose thermostat opens up to allow flow to the radiator. During this critical warm-up period if there is no flow of coolant through the head, hot spots can develop in and around the cooling passages around the combustion chamber area and actually boil off the coolant as it becomes overheated. This is why it is critical to maintain a "minimum" flow of coolant liquid through the head at all times.

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

flash7210 wrote:

An old thread brought back from the dead :shock:

jeepsterkj wrote:

The "inline" is a Renault 5 thermostat...

I hate to be the one to completely invalidate your detailed and well worded post, but the inline thermostat is no longer a recommended solution.

Dont do it!

I've been there, done that, and cracked a head.
And I'm not the only one that its happened to.

If any of the forum moderators read this, I recommend that this thread be locked.

I would not lock this thread now that you and WWDiesel have posted contrary opinions.

I still do not recommend the ARP head studs unless you are building a high performance engine, but essentially you and WWDiesel are correct; any inline thermostat for the Liberty CRD is a BAD IDEA.

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

What's the thought process opposing ARP studs?

Inline thermostat issues

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