How to replace the Thermostat

[zebelkhan]

Has anyone replaced the thermostat on their MO? I read the SM and it seems easy but not sure about accessibility. Dealer wants $250 to do the work.

Yesterday the engine temp went up again and when I stopped it did not come down fast enough. However, as soon as I reved the engine it dropped like a rock! So either water pump is out or the thermostat is not fully opening. I don't have any noise so it probably is not the water pump. What do you guys think?

[njjoe]

z-

I doubt it is the water pump. The MO's pump is chain-driven so there is no belt to slip. If the seals were bad you would smell the coolant but that would not affect the pumping efficiency.

A balky thermostat could be responsible. However, for some reason I thought the thermostat was designed to fail in the OPEN position. Obviously I am wrong on that one.

I assume you have no leaks and the radiator is full, correct?

-njjoe

[Eric L.]

You mean while you revved your engine in Park or Neutral, and that caused the temp to go down? Or that the temp went down once you got moving again?

If its the latter, I suspect a bad radiator fan and not the thermostat.

[zebelkhan]

Radiator is full, there are no leaks, and last time I was at the dealer (right before my extended warranty expired) I complained about it and of course they suggested to pressure test the system which I agreed to just to make sure they document the problem. It passed the test with no issues.

Why would revving the engine (not moving the car) drop the water temp so fast, I am talking about 1/4 of the gauge in two seconds! Obviously hot water was replaced with a rush of cooler water from the radiator. Could it be trapped air in the cooling system? But if that was the case it should overheat all the time, not just under load....

[njjoe]

z-

Maybe it has to do with the increased volume of water flowing past the thermostat, or possibly the vibrations from the increased rpms that causes the balky thermostat to open. I'm not sure.

-njjoe

[zebelkhan]

Let me revisit the problem.

Temp gauge is always normal, except when it gets hot outside. Even then it stays at normal unless one of the following situations are also present:

1- Extended acceleration that lasts for several minutes.
2- Climbing hills for several minutes.

I have always slowed down or released the load on the engine at the first possible moment so I don't know if there is a point at which the temp maxes out. Frankly, I don't want to try it either.

Possible reasons for the problem:
1- Cracked head and/or blown head gasket - Ruled out because over heating happens only under load. Besides, I do not have contaminants in oil or water.
2- Low water level, leaking radiator, bad cap, plugged radiator - All of these ruled out by dealer when they pressure checked the cooling system.
3- Lean fuel mixture or incorrect engine timing - A possibility, but unlikely as I do not experience any of the other symptoms associated with those.
4- Low airflow to the radiator - Ruled out as both fans operate and there are no sir restrictions, other than my homemade lower grill which I don't think creates significant restrictions.
5- Bad water pump - I think I can rule this out too because when they go they make lots of noise and I do not hear anything.
6- Air in the cooling system - A possibility worth exploring
7- Bad thermostat - I agree with joe that thermostats are designed to fail in open position so this is probably not it but perhaps worth exploring.

Any other ideas?

[zebelkhan]

This is what I got a couple of days ago as I was climbing the hills. It was normal before that, and became normal after the climb was over. It was 95 degrees outside and my air was on.

[Eric L.]

Zeb, I'd just replace that thermostat anyways - its the cheapest part of the cooling system and if it fixes the overheating issue, then great. If not, at least you've ruled out a part that wasn't that expensive to replace anyways. If you are not losing coolant, its probably not a bad head gasket, and if the fans are working properly, then its probably related to fluid flow, in which case I would suspect the thermostat, radiator core, or even an internally collapsed hose.

[zebelkhan]

I am just being cheap! If I had a garage I would do the work myself because the part is cheap, around $25. But I just don't want to pay someone $250+ and not have the right results. However I may not have a choice.....

[MOpar]

How about checking the electrical connection to the sensor (sending unit)??

[risaralda]

Originally posted by zebelkhan
I am just being cheap! If I had a garage I would do the work myself because the part is cheap, around $25. But I just don't want to pay someone $250+ and not have the right results. However I may not have a choice.....

Mr Z, how about doing it at my garage, let me know or give me a call.

[zebelkhan]

Originally posted by risaralda
Mr Z, how about doing it at my garage, let me know or give me a call.

That is very nice of you to offer. I think I will take you up on that! It is time to visit and have a cold one anyways. I will call you...