Yesterday I was having some issues with my temp gauge climbing closer to 250 degrees than I would have liked while going up some long grades. It has been a while since I have replaced the thermostat so I thought I would try running a cooler t-stat just to see what would happen. My 95 ZJ with the 4.0 came with a 195 degree t-stat from the factory. I installed a 180 degree t-stat today for ***** and giggles and gave it a good test drive. This is what I found, the engine temp while on the highway was lower by about 10 degrees. Was it at 180 degrees? No, but it was lower than 210 degrees. The temp while sitting in traffic still went to almost 215 degrees, but dropped bellow 210 after a few miles once I got moving. The outside temp was about 100 degrees and I'm running a 50/50 mix of coolant. I also replaced the t-stat housing just to be safe. So there you have it, a cooler t-stat will run cooler while moving but won't do much sitting still.

 

I think it runs hotter sitting still because of less airflow thru the rad. I don't think the clutch drive fans are worth a whole hell of a lot. They do save a little horsepower, but lack the airflow of a direct drive fan.

The electric fan in my WJ cuts in at about 215* and shuts off at about 205*. So far, it has worked perfectly and my temp has never gotten over 225* EVER, and that was pulling up a long hill fully loaded with the OAT at about 95*. (I wasn't running my A/C)

You are right about the thermostat, though. It OPENS at set temp, keeping the engine at AT LEAST that temp. Airflow and the radiator control the rest.

 

An E-fan conversion is in the future, too busy prepping for the long arm lift now.

 

I just posted a thread, about my t-stat, but without it, the temp is not higher than 180F with climate. So in my case that is what the cooler and the airflow can do. With the t-stat it's boiling I attached a picture to my post, where the t-stat is in boiling water, but it opens only 2mm.

 

I'd think you need a new one.