Thermostat Temp Differences

How do I know what thermostat I should use with my '99XJ (4.0L, AW4)? I see the local auto parts store sells 160*, 180*, and 195* models. My XJ is stock and gets hot summers and cold winters. No towing yet, but if I get a hitch it would do only the rare utility trailer with a riding mower on it.

How do I know what I should use?

Run the 195. The computer takes inputs from the coolant temp sensor, may as well use the thermostat the factory programmed everything around. Some claim it makes no difference... I'd run the OEM part and not second guess the Mopar engineers on this one.

yossarian19 said:

Run the 195. The computer takes inputs from the coolant temp sensor, may as well use the thermostat the factory programmed everything around. Some claim it makes no difference... I'd run the OEM part and not second guess the Mopar engineers on this one.

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That was kind of my train of thought too, but my train of though normally derails.

scott00tj said:

That was kind of my train of thought too, but my train of though normally derails.

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Definitely the 195degF unit. I've had the most consistent results with the OEM ones, but there's also some strong recommendations for the Stant SuperStat Premium. Both have worked well for me in the past, but after a bad run locally of the Stant items in multiple vehicles I went back to OEM. YMMV.

Having said that, you may want to also run an 8-hour chemical flush on the cooling system, change the coolant (I would recommend using pre-mixed coolant and diluting as necessary with neat antifreeze / distilled water), and see what improvements you get. From there, your options for better cooling without getting too wild are basically 3-row radiators and the ZJ heavy-duty fan clutch. Also take a look at the serpentine belt tension (may not be driving the water pump and mechanical fan fully) and water pump - it's not unknown for the impellers to gradually corrode over time, reducing water flow but leaving the pump appearing otherwise-functional from the outside.

195 degree all the way.

I like both stats from Jeep and the Stant SuperStat.