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Over Cooling?......hahaha

 

In all seriousness, make sure you have a good 195 degree T-Stat.

 

I made the post and realized I couldn't delete it . I'm going to put my old fan clutch on an see if the new one is stuck, if not then I'll replace my thermostat. As for the overcooling yeah kinda odd for a the 4.0 XD. I just went on a road trip with hills and was confused as to why my mpg stayed around 21 even though the temp was below 150.

 

Is the gauge correct? I can't see how the fan clutch could cause overcooling. Is it locked up or overly noisy when the engine is cold?

 

I believe the mechanical fan clutch is stuck in the on position. When I get on the highway the temp goes down to 140. It could be the temp sensor on the back of the head but I replaced it a few years ago.

 

I would say the engine is pretty noisy on startup. Engine is healthy so nothing mechanically wrong.

 

Maybe you should buy or borrow an infrared thermometer gun and verify the coolant temp at the thermostat housing.

 

Test the gage temperature sensor with an ohm meter at both warmed up and cold conditions. make sure the gage is right. A locked up fan is easy to diagnos, no need to swap one to find out. when cold, turn it by hand (engine off) if it spins easy, it is not locked.

If the fan is good, and the gage is correct, i.e. you are running cold, check the thermostat.

Good luck

ps.... Is this a four or six cylinder? If a six, then your mileage is much too good!

 

Inline 6 (manual) and the mileage is no joke with no mods.

 

He's talking about highway mileage, so it's not all that great for a properly running Cherokee. I normally get 18 combined city & highway.

 

My fix for this issue was a fan cluch replacement. The fan wouldn't move freely cold. The final result took this long because I got 2 broken fan cluches in a row and the final one worked. Temp stays between 190-210.

 

And just curious, what do you get on the highway? I thought 19-21 mpg was good? I've seen posts of people happy with 14 mpg.