OEM thermostat Review

racertracer · **Posted:** Tue Dec 14, 2010 7:41 am

My thermostat is original and what i've noticed is that the needle sits 1 to 2 digit above the quarter mark almost all the time except when the turbo has been put thru a full boost, then the needle moves to just below the half way mark and sits there for a while and then moves back down to the quarter mark while drving at normal speeds.

I am wondering if the way the thermostat is functioning presently is infact beneficial to the turbo cool down, since it cools the engine quickly, any ideas?

Also, I would like to hear from those of you that replaced your thermostat with a new OEM thermostat:

Have you noticed any difference?

Does the cabin get warmer sooner?

Have you noticed an increase in MPG or better engine performance?

I am thinking that if there is minimal gain when changing the thermostat, then I don't see a need to replace the original, my viscous heater works fine and so does the heated seats.

Joe Romas · **Posted:** Tue Dec 14, 2010 8:57 am

I replaced mine with an OEM. Before it started failing, the original stayed one tick below center as shown as 176f on gde's chart. The OEM replacement runs between one tick below center and center so it's running a tad warmer. How ever both my VAG-COM reading the coolant temperature and my non contact laser thermomentor on the thermostat housing by the cylinder head shows it's 176f eactly :shock:

I didn't check what it was before it started failing.

CIMARRON13 · **Posted:** Tue Dec 14, 2010 12:32 pm

I replaced mine about 2,000 miles ago with OEM. Had the same issues with the thermostat running open and not getting to half way mark on temp gage. Now CRD will get to half way mark quickly and maintain itself. Coldest morning was around 32 and jumped right up to temp after a couple miles. I haven't seen any mileage increase which I thought I might. I still have a problem with overheating on steep grades driving around 30-40 mph. Had to pull over driving in Big Bend NP going up to the mountain lodge. Needle was heading to red quick before I pulled over. Need to check to see if fan is working.

audiboy86 · **Posted:** Tue Dec 14, 2010 12:50 pm

Mine is doing the same thing about 1 or 2 ticks above the 1/4 mark. Mine is being replaced with the OEM and my other one is going to be sent to kapalczynski to be machined and converted to 192F. That is unless one of yall want to send me your old thermostat i am willing to pay to ship it ?

FormerlyBankNote4x4 · **Posted:** Wed Dec 15, 2010 8:06 am

CIMARRON13 wrote:

I still have a problem with overheating on steep grades driving around 30-40 mph. Had to pull over driving in Big Bend NP going up to the mountain lodge. Needle was heading to red quick before I pulled over. Need to check to see if fan is working.

There's a TSB for that. Calibration is off, I think it's a ecm flash to fix.

Joe Romas · **Posted:** Wed Dec 15, 2010 8:15 am

FormerlyBankNote4x4 wrote:

CIMARRON13 wrote:

I still have a problem with overheating on steep grades driving around 30-40 mph. Had to pull over driving in Big Bend NP going up to the mountain lodge. Needle was heading to red quick before I pulled over. Need to check to see if fan is working.

There's a TSB for that. Calibration is off, I think it's a ecm flash to fix.

A bad fan cutch can cause that too

If yours does not sound like a jet engine it's bad (no kidding)

CIMARRON13 · **Posted:** Wed Dec 15, 2010 2:00 pm

Joe Romas wrote:

FormerlyBankNote4x4 wrote:

CIMARRON13 wrote:

I still have a problem with overheating on steep grades driving around 30-40 mph. Had to pull over driving in Big Bend NP going up to the mountain lodge. Needle was heading to red quick before I pulled over. Need to check to see if fan is working.

There's a TSB for that. Calibration is off, I think it's a ecm flash to fix.

A bad fan cutch can cause that too

If yours does not sound like a jet engine it's bad (no kidding)

Just got GDE eco-tune so that should have the updated flash if that is the fix. The fan would come on with AC running this past summer. Time will tell now I I still have a problem.

UtopiaCRD · **Posted:** Wed Dec 15, 2010 2:30 pm

CIMARRON13 wrote:

Just got GDE eco-tune so that should have the updated flash if that is the fix. The fan would come on with AC running this past summer. Time will tell now I I still have a problem.

That's the electric fan for the A/C condenser, not the mechanical fan attached to the engine. The clutch in the mechanical fan causes it to engage to full cooling power when needed (the jet engine sound referred to). You can't tell if it is working by looking at it, as it still spins some even though not engaged.

Joe Romas · **Posted:** Wed Dec 15, 2010 8:10 pm

CIMARRON13 wrote:

Just got GDE eco-tune so that should have the updated flash if that is the fix.

Not totally positive but as I remember the flash for the temperature guage might have been in the BCM (Body Control Module). You may want to contact GDE to make sure :BANANA:

ATXKJ · **Posted:** Wed Dec 15, 2010 9:49 pm

to racertracer
my Thermostat was just above 1/4 - scangauge said 135-140 range
put on a new OEM Thermostat and the gauge is now a hair left of 1/2 and the scangauge says 170-175 - drives a lot better.

CIMARRON13 - when I went up to Colorado climbing mountain passes - mine would act like it was overheating - I took it in for the flash - didn't seem to change much - however I never heard the Fan engage - so before I go back to Colorado - I'm going to change the clutch.

danoid · **Posted:** Wed Dec 15, 2010 11:05 pm

Joe Romas wrote:

CIMARRON13 wrote:

Just got GDE eco-tune so that should have the updated flash if that is the fix.

Not totally positive but as I remember the flash for the temperature guage might have been in the BCM (Body Control Module). You may want to contact GDE to make sure :BANANA:

The engine reports a temperature, it's up to the BCM and cluster to move the gauge. The 'fix' was was a BCM reprogram only to make the gauge lie and stay in the middle more often. Top of the scale is still top of the scale and no matter what software you have in the engine or BCM you aren't in trouble until it chimes at you. Then it will cut power. This has only happened to me while...
1) climbing a decent grade with a 5600# trailer in second gear with the torque converter unlocked,
2) climbing a steep winding grade with no trailer but only about 15 mph with the torque converter unlocked,
3) doing a ridiculous multiple doughnut in sand in first gear.

With a properly functioning cooling system it's darn near impossible to overheat if you're going fast enough to keep the torque converter locked, there's just too much engine grunt to not make it up the hill. If your vehicle is truly overheating (setting the seat belt chime and cutting power) and you are not doing something similar to the three scenarios above, check your fan clutch, coolant level, hoses, etc.

If your temperature gauge is not reaching within a tick or two of halfway under normal driving, then you thermostat has likely failed.

GreenDieselEngineering · **Joined:** Sun Jun 07, 2009 5:10 pm **Posts:** 1111

Danoid is right with his assessment.

The overheat protection in the engine software will automatically cut off the AC and slow the vehicle down to about 25 mph in full overheat protection. When this occurs the engine is at its maximum operating temperature. In this situation we would put the heater on max fan and max heat to help cool off the system and also put vehicle in park and rev engine to 1500-2000 rpm so the mechanical fan pulls more air through the radiator. More transmission lock-up will reduce heat load to the trans fluid and improve towing capability.

Of course, no overheat system will save an engine with a blown coolant hose. This is always a consideration if the overheat chime goes off and worth a stop to check for leaks.

audiboy86 · **Posted:** Thu Dec 16, 2010 12:15 am

I know my Thermostat is gone i don't get much above the 1/4 since it got cold down here. But i have had mine over heat on the way home from work one night and the only thing i could find wrong with mine was my Coolant had dropped below the min mark on the tank. I just refilled it and fixed my leak and haven't had it over heat again.

crdjoe · **Posted:** Sun Dec 19, 2010 8:30 pm

Mine was running like s#@% and the gauge was 1 or 2 needles above a quarter point on the gauge with the grille nearly completely blocked I bought the new one installed it kept my fingers crossed and the gauge sits at 1 needle below halfway when fully warmed up with the grille still blocked. It definitely runs better and the heater is a little warmer 2.

CRDMiller · **Posted:** Thu Dec 23, 2010 11:41 am

I have a new oem thermostat, and an after market coolant gauge, my factory temp gauge does not move from about one tick below 12 (around 11:40) from 165 to 230 Degrees, but then jumps instantly to approximately 90% of the OEM gauge between 230 and 240f.

I have tried multiple locations for the after market probe (between the egr cooler and the tstat housing/and the t stat housing to pressure bottle) and the results are consistent. I realize that the oem gauge is pulling data from a sensor located in the head, and that is is possible that thermostat housing outlet or egr cooler outlet temps are higher than the head probe temperatures but coolant that hot, to hot. I can be sitting at 230f and my oem gauge says that things are just fine. For the record my egr is plated off from the exhaust side, I have no fcv butterfly, and I have disconnected the airflow sensor in the air box, my egr is as disabled as it can get.

Does anyone else have any data with an after market coolant gauge?
I suspect that many of us can be at "to hot" without knowing it, perhaps related to the handful of cracked heads we have seen. I'm no engineer but i consider radiator inlet temperatures in excess of 220 to be a problem. If for no other reason that the oil pressure drop that I see at those temps.

What do you guys think?

racertracer · **Posted:** Thu Dec 23, 2010 4:40 pm

More data would help.

CRDmiller, where did you install the after market coolant gauge and sensor?

grywlfbg · **Posted:** Sun Jan 02, 2011 1:02 am

Thanks for the info here. Looks like my thermostat is failing. Temp gauge isn't going as high as it used to and mileage is in the toilet (19.8 on the EVIC lately - used to be 26 around town). The waiting list for Mark's thermo looks pretty long so I'm going to buy a new OEM one and send him my current one for his fix. Once I get his installed I'll donate that one as a core for others to get Mark's version.

Do I need to do a full collant flush when I change the thermostat or can I just catch what little spills out and top it off after installing the new one?

DynoPax · **Posted:** Sun Jan 02, 2011 11:43 am

grywlfbg wrote:

Thanks for the info here. Looks like my thermostat is failing. Temp gauge isn't going as high as it used to and mileage is in the toilet (19.8 on the EVIC lately - used to be 26 around town). The waiting list for Mark's thermo looks pretty long so I'm going to buy a new OEM one and send him my current one for his fix. Once I get his installed I'll donate that one as a core for others to get Mark's version.

Do I need to do a full collant flush when I change the thermostat or can I just catch what little spills out and top it off after installing the new one?

Unless you are scheduled for coolant flush & replacement, just top off when thermostat is replaced... I'd say you lose approx. 1 to 2 cups of coolant, so no big deal really.

grywlfbg · **Posted:** Sun Jan 02, 2011 3:19 pm

DynoPax wrote:

Unless you are scheduled for coolant flush & replacement, just top off when thermostat is replaced... I'd say you lose approx. 1 to 2 cups of coolant, so no big deal really.

Thanks! Jeep is coming up on its timing belt extravaganza next year and will replace coolant as part of that so was hoping to not do it twice.

LibertyCRD · **Posted:** Mon Jan 03, 2011 8:52 am

Now that the weather is cold again, I'll share my experience. Last Winter, I had a faulty t-stat. My guage read between 1/4 and 1/2 all the time. It was obviously running too cool. I was getting 19-21 miles per gallon.

During the Summer, I replaced the t-stat with a new unit at a cost of $125. Ouch.

It is Winter again and it's been very cold for over a month now. My guage reads 1/2 all the time! YAY! However, I am STILL getting 19-21 miles per gallon. So the new t-stat has not improved mileage at all.

As far as cabin heat... I do not have more cabin heat now than I did last year either. Jeep would still get very toasty inside even with a faulty t-stat.

I'd say the only reason to change the t-stat is just for the health of the engine. Performance-wise, it doesn't help any.

OEM thermostat Review

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