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New Motor Running Cool

OK. They opened at 195,... progressively or quickly? Here is the theory,... if the thermostat open (even at the desired temperature) all the way out quickly, it will allow the hot water to flow to the radiator. Cool/colder water will take its place. This cold water being colder than the thermostat specs, it will close again until the water that surrounds in the thermostat housing reaches the 195 set temperature then it will open again. This could be repeated several times before it settles down.

When I tested those I had, I would allow it to open fully then add some cold water (not a lot) to see how quickly it closes and at what temperature then allow it to get hot enough to open again. I repeated it several times noting how quickly it opens and closes and whether or not it opens and closes completely with minor temperature changes. I find the OEM unit to open in small increments thus doing a better job at controlling temperature.


Here's the answer right under your nose.

Techno1154's scientific analysis verifies my real world experience with the factory stats. What a great contribution. Techno, can I copy your analysis for future use on forums?
 
Not sure if serious.

Did two different t-stats with the same result. Both opened slowly at their spec'd temp so nothing was abnormal there.

I am starting to think my new radiator may have too much cooling power.
 
Not sure if serious.

Did two different t-stats with the same result. Both opened slowly at their spec'd temp so nothing was abnormal there.

I am starting to think my new radiator may have too much cooling power.

Read it again.....

He's saying the aftermarket stat opened too radically each way whereas the factory stat had much better control.
 


Temp on Front of Thermostat Housing

IMG_0723.jpg


Thoughts

  • Very strange that the dealership part was made by Motorad (same make as my first thermostat) rather than MOPAR.
  • I think my poor gas mileage (13mpg) could be attributed to running cool
  • I could try a NAPA thermostat
  • Maybe my pump is too powerful
  • Maybe my radiator is too effective

Any thoughts?
Just for the sake of experimentation, spray some cheap, flat black paint on the thermostat housing. Then take your reading off that spot. Some IR thermometers can give a false reading off a reflective surface.

I am running a Stant thermostat and am happy with the results.

Losing 5 mpg is pretty significant, I am guessing the ECU is not going into closed loop. Time to plug into the ECU and start looking at all the sensor parameters.
 
Holy shit guys!! Just put a different stat in it!!

I am not opposed to it but I have already tried a Motorad stat and one I bought directly from Jeep (which although it came in a Mopar box, was made by motorad). If you’re recommending a stat from Jeep, I’ve already got that in there now.

This morning I covered 4/5 of the radiator with cardboard and that made no difference. Very strange.
 
I am not opposed to it but I have already tried a Motorad stat and one I bought directly from Jeep (which although it came in a Mopar box, was made by motorad). If you’re recommending a stat from Jeep, I’ve already got that in there now.

This morning I covered 4/5 of the radiator with cardboard and that made no difference. Very strange.

What stat did you get from the dealer?
 
Jeep gave me MOPAR 83501426-AD

From what I gather, all of the thermostats Jeep sells are now made by Motorad. They come in a Mopar box, but they all have Motorad stamped on them.
 
They have been made for Mopar by Motorad for many years.

But, the ones the factory got were different than the aftermarket ones.

Can you compare the stampings between the aftermarket and Mopar stat?
 
They both read the same as I recall.

"91C 195F" with Motorad stamped on the support.

The main difference between the two was that the 'Mopar' stat had a jiggler the valve.

I am reading through all kinds of threads right now. Seems many people have had this issue and no one ever finds a cure all solution.

The most common suggestion is buy form the dealer, which I already have. But I think the dealer stats of yesteryear are on a higher plane of quality than what they are selling now.

Also it seems everything is made in Israel. My guess is these things are all the same, just bought by various white label brands and sold under different names.

Next steps? I don't know. Considering trying a NAPA stat. Or a 210* stat. For the moments I am continuing to read...
 
I had a problem just like this, turned out to be an after market thermostat housing with clearance issues. It was putting enough pressure on the tip of the thermostat to cause problems.

Good Luck,
Mac
 
I had a problem just like this, turned out to be an after market thermostat housing with clearance issues. It was putting enough pressure on the tip of the thermostat to cause problems.

Good Luck,
Mac


That's one to file away in my memory banks......

Reverse engineered parts from WunHungLo and his comrades........
 
Thanks for posting, Mackie.

Put a 205* t-stat in yesterday from Napa. Also marked Motorad.

Gauge temp while driving (heat off): approximately 205*
Gauge temp while driving (heat on): approximately 182*

Gauge temp at idle: approximately 205*
T-Stat housing temp at idle: 208*

Although it's less drastic now, still not a huge fan of the temp fluctuations and the expansion/shrinking of parts.

The only explanation I can come up with for running at temps below the t-stat rating, is that the t-stat is not closing completely. Or perhaps the t-stat is not creating a good seal on the front of the block, and coolant is pushing by.

I'm going to drive it for a few days and see if it levels off.
 
With the heat on you are are seeing some cold coolant from the heater core exit, enter the water pump inlet and by pass the radiator and T-stat in a loop. Some of it may be bypassing the block and showing a fake CTS temp on the dash?

I need to look at the water pump, T-stat housing lay out again to be sure.

I know it bypasses the Radiator and the T-stat for sure.


Thanks for posting, Mackie.

Put a 205* t-stat in yesterday from Napa. Also marked Motorad.

Gauge temp while driving (heat off): approximately 205*
Gauge temp while driving (heat on): approximately 182*

Gauge temp at idle: approximately 205*
T-Stat housing temp at idle: 208*

Although it's less drastic now, still not a huge fan of the temp fluctuations and the expansion/shrinking of parts.

The only explanation I can come up with for running at temps below the t-stat rating, is that the t-stat is not closing completely. Or perhaps the t-stat is not creating a good seal on the front of the block, and coolant is pushing by.

I'm going to drive it for a few days and see if it levels off.
 
He got another flakey thermostat.

It is possible.

Baltanakt, Why did you not say in the beginning that you were running the heater on? That make a huge difference regarding the cooling system.

My XJ have no mechanical fan and have not had one since 2003. Yet, when running the heater on high with the ambient temperature between 40 and 50 degrees the engine temps remain low, i.e. 185 to 195 degrees as long as the speed remains 45 MPH and above. No biggie there and no need to complain about it.

I do not know if that is what is happening to your XJ but,.... turn the heater off and go for a run then report back.

My previous XJ, a 1994 model had a mild over heating problem for awhile which manifested itself when driving hard through the hills of East Tennessee. To reduce the temps, all I did was to turn on the heater full and watch the gauge return to a more normal position. Do not under estimate a good cabin heater in the XJ.
 
@techno, all readings posted were without heat unless stated otherwise.

So I've had the 205* stat in for a week or so now.

With heat on it is running about 182. Sometimes on the highway it seems to dip down to 175. Wheeling at a very slow pace up hill in snow I got to about 200.

My mileage has gone up to 17MPG, but I would expect it to be a little higher with new O2 sensor, full 2.5" exhaust, rotor, cap, wires, plugs, head job, etc.

Anyways, the dips into the 170's don't sit well with me as I'd prefer the engine to run consistently around 210*.

I've read dozens of threads regarding temp fluctuations and running cool and it seems it's anybodies guess what is causing the problem. One guy will say he solved it with Brand X thermostat, another will say Brand X didn't help at all.

I am considering, as some point, trying a restrictor like this: http://gojeep.willyshotrod.com/HowtoRadiatorRestrictor.htm
 
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