Thermostat replacing with a cooler one


I have a 1998 Jeep Cherokee Sport with a 4 liter 6 cyl. motor. I tow a camper trailer and would like to hear the pro’s and con’s about replacing the thermostat and temperture sensor with ones that are set for a lower temperature.


Twenty years ago I’d say “OK”. But with today’s engine management computers, I think that you’ll be confusing “HAL” and may experience something bad by trying to out think the computer. Logically the colder thermostat will opne at a lower temp, right? So it will run at a lower temp, never really heating up . . except that the computer will probably try to compensate. Are you running hot? What is the problem besides the anticipated towing?


What are you trying to accomplish? Do you have a standard or automatic transmission?


I sometimes experience a “hot” runnig engine, while idling. It has never overheated. I bought the Jeep in 2001 and believe the original thermostat and temp sensor are in the Jeep.




There is nothing to be gained in a 1998 vehicle.

Engines are more efficient at their design temperature.

Putting in a lower temperature thermostat will not allow the engine to reach its optimum operating temperature resulting in lower mileage, possible moisture problems and increased wear. It may also reduce performance.

Many people who have over heating problems like to try lower temperature thermostats. That will not fix the problem because once the temperature gets to the design temperature of the thermostat any temperature thermostat is fully open and there is no more.

If you have overheating, lets talk about what you can do to fix that.


You will get the greatest benefit from installing an external transmission cooler. This will take heat off your engine and greatly extend the life of the transmission.

Engines are designed to operate at a specific temperature. Lowering that temperature from 192 to 160 is asking for trouble. A 180 degree thermoststat MIGHT offer some overheat insurance and not hurt anything…You should change back to 192-195 for winter driving to prevent sludge build-up and get decent heater output…


I have a tranmission cooler already. Added it soon after buying the Jeep. It sound like the best thing to do is change the thremostat with one to the manufactures specs.


I am not overheating, I just beleive he thremostat is getting old. It is very possible the one in the Jeep is the original unit. I have added a tranmission oil cooler and had installed a thicker core (after market) radiator. I just want to protect the motor and transmission as much as I can from overheating, before it happens.


Best things to do do reduce chances of overheating:

  1. Coolant flush, replace with fresh 50/50 antifreeze/distilled water mix
  2. Clean off any bugs and debris on the radiator
  3. Make sure the fan is working properly
  4. Inspect and replace if necessary all coolant hoses and clamps
  5. Replace water pump if you feel like spending the money (or suspect it’s old and/or worn out)
  6. Change your oil and filter - up to 80% of the engine’s heat is absorbed by the oil - if it’s clean and flowing well it can absorb and remove more heat.
    6b) If possible, install an oil cooler.
  7. Don’t use the A/C - it just dumps extra heat into the engine compartment.

At any rate, a cooler thermostat won’t make a lick of difference. An engine will overheat if it has a 100 degree TS or a 200 degree TS, it doesn’t matter. All you’re doing by putting in a cooler thermostat is getting coolant to radiator earlier, but the engine will still heat up, it might take a little longer. But if it’s going to overheat, it will.


Oh, and replacing the thermostat because it’s old isn’t a bad idea, but just get the OEM one.


JMHO, but I change thermostats every 2-3 years, bad or not. It’s cheap insurance is the way I look at it considering the number of engines that are barbecued every year because of a 5 dollar item.

You should stay with the original specification thermostat.


I have done or do most of the things you recommmend. I have been looking for an add on engine oil cooler for a Jeep of my type, but have not found one. As far as the water pump, I do not think its worn or operating poorly. I have not changed it, but do not think it needs to be changed. How can one tell if it is worn or not working correctly? I do not want to spend money I do not need to spend.

I will however change the thermostat soon.


I plan on replacing it. Do you recommend a brand?


To the best of my knowledge, the only sure way to check if the water pump is in good shape is to remove and inspect it. Obviously, that’s not always an easy task (which is why it’s often recommend to replace timing belt-driven pumps when replacing the timing belt.) But if it seems to be working fine (that is, the car isn’t overheating) chances are it’s okay.

I don’t know off hand of any Jeep oil coolers, but it might be worth investigating some aftermarket coolers, such as a B&M cooler here:

Also, you could try an see if an oil cooler from a Ford Crown Victoria police interceptor might work. I don’t know if it would, and might take some work to get it in, but I would think that’s another option.