right before i bought my xj the guy put in a new water pump and tstat he put in a 200 degree is what he told me. now that i have it apart should i run a lower degree tstat? id like it to run cooler and my open system install is about done so now would be the time to do it. will i gain much installing a lower degree stat?

 

Depends on what u mean by "gain much". T-stat does one thing....control minimum coolant temp.....the rest of the cooling system and its condition along with ambient temp and driving conditions control max coolant temps. FWIW, we use a 180 year round.

 

Is it a daily driver or trail rig if its a daily driver I wouldn't go below 180 that way u will. Still have ur heater in the winter time mine is a trail rig and I have a 160 with gears and crawling around it still gets up around the 200 mark then ill kick the electric fans on and it drops down pretty quick

 

I have run 160 and 195. For the daily driver like mine the 160 was a mistake and am glad I'm back to 195. Car just seems more efficient and runs better not as cold. I am sure there are techs out there but this is a jeep and I can't see a benefit from The 160 with factory tune

 

x2 it's not the 70's anymore. Engines are tuned to run most efficiently at a specified operating temperature, which is usually around 200F. A cold engine will get poor mileage

 

x2. I run a 180* and like it. it sit right 195*ish just below half mark and like it. used to run at 210* all the time before my new radiator/fan/t-stat/water pump ect... maybe i am a bit paranoid since i have a 2000 with a 0331 head casting but I would recommend a 180* to anyone any year 4.0L. 210* seams just a bit to hot for me, but isn't "overheating"

a 195* is factory temp setting. anything below a 180* is to cold in my opinion. i have ran a 165* and it wouldn't really worm up at any temp below 50* out side. switched it out after 2 days.

 

If a cooler running engine is what you want, run a higher capacity fan and/or an adjustable thermostat. Running a cooler thermostat is just going to keep the cold start injector on longer if not all the time. That is not good, not only for your gas mileage, but running that much fuel all the time increases your risk of cylinder wash. Just do it right, and start with an adjustable thermostat so you can bring the fan on sooner, and if you still need more cooling then add a two or three row radiator to your car.

 

The 195 degree factory temp is best for the vast majority of 4.0 applications.

As for brands, I buy my thermostats from Jeep and also like the Stant SuperStat.

There is no shortage of crap, cheap-charly thermostats out there. Spend the extra $5.00 and get a good one.