Baystate Jeepers

I've got a 4.0L 98 Cherokee with an overheating issue. The head was just decked and a new gasket was put in. Fluids were filled and air removed from the system best I can figure. I used a funnel that replaces the radiator cap so I can keep the level of fluid well above the highest point within the engine and let it run and draw the fluid from the funnel as air moves through the radiator. Once the level stopped moving and the engine was warm, I shut it off leaving the funnel with fluid still attached and made sure the level never went down so air never entered the system. Once it stopped moving, I plugged the funnel, removed it and replaced the radiator cap.

I can run the engine for 5-10 minutes and the needle doesn't move from just over 210 on the gauge. Then seemingly randomly it jumps to the red and I shut it down. Over flow bottle is nearly full and there doesn't seem to be any leaks, and there isn't any clouds behind the jeep.

Thoughts?

Fan running? Thermostat in right way. There is a fan relay under the passenger side headlight [atleast on grand cherokee] that is known to go bad. If jeep has a/c turn it on, it automatically turns on fan that way so you don't need to overheat it to find out.

Def agree on the fan, and double checking the T-Stat, I know most fail open now to avoid that problem but prob not all do that. Also, is the temp sensor operating correctly? might be worth checking around with a temp gun and see if things are that temp or if its bad.

The main fan runs constantly, will need to see if the electrical fan spins up. Neglected to notice that. The thermostat was put in with the spring inside the block, I believe that to be correct but not 100% sure. The last couple times I ran it this eve the radiator cap started spewing fluid before the temp gauge spiked. I shut it off at that point.

I'll check the electrical fan using the AC tomorrow first thing. I've got the day off and can putz around with it a bit in the morning.

Also, its worth a check of the clutch on the fan as well to ensure function. Easiest way I have heard of checking it, and laugh all you want but it worked for me, was to take a rolled up newspaper and attempt to stop the fan with it, if the clutch is shot and just kinda spinning the fan but not moving it enough it will stop the fan without problem, if the clutch is good, youll have confetti.