pretty much same for me. Im used to renix too.

Ill have to get a IR thermometer and check hers. I think her dad put a cool thermostat in it though (instead of being stuck open)

yeah man... i wasn't talking about my 96 - on which the temp sensor (on tstat housing) and gauge sender (on engine block) are separate! ... 97 and on things changed .... they combined the temp sensor and gauge sender onto the tstat housing .... either way, the temp sensor on the tstat housing does have everything to do with the delivered fuel ratio and does affect overall performance because the ecu uses the resistance readings to make necessary adjustments (you can test this by pulling the sensor and placing it in hot/cold water and you will see the resistance value changes affect the ecu fuel ratio adjustments).

Alpine ..... besides the tstat (which, if faulty, you should replace with a good quality 185-190 degree), you should also check your tstat housing for crack/leak, including gasket and water pump (the stock water pump impeller is not the best and can break/seize) - all can cause poor circulation issues ... the fluid dynamics is a good choice to go with, ditching the heavy stock mechanical clutch fan and electric fan .... good luck!

Hate to bring up an old thread, but I have been doing some research that led me to here.

I just replaced my thermostat with a duralast one about 5 months ago and had no major issues.

I just replaced my water pump however and since it was a newer thermostat I just left it in place.

AFter replacing the water pump I drove it around and the temp was fine, heated up to where it normally would.

Drove the day afterwards and then the xj wasn't getting up to operating temperature. Maybe 110* I also didn't have any heat. I jumped out and felt the upper rad hose that connects to the thermostat housing and it was warm but not scolding hot. There fluids in it as well.

Sound like a thermostat to you guys? I'm not sure where else to start?