OK guys here it is. Just looking for some opinions here. About 6 months ago I replaced the 4.0 in my 87 Comanche with an HO from a 93. Replaced water pump, thermostat, and upgraded to a 91+ radiator. Also replaced all the hoses. Lately she's been running hotter than normal, 210+ on a 180° thermostat. I swapped a different clutch fan on for fun, no change. Now I've tried 3 t- stats and removed it as well. Also removed the WP to inspect pump and seems fine. It still runs hot. It runs hot on the freeway in 5th and in stop n go. If I rev it to about 2500 it cools a little. Seems like when I park it it has lots of pressure but the radiator is cold. Has anyone had his problem? Heard of different pumps ever? Thanks

 

Have you replaced the upper and lower radiator hoses? When they get old they tend to collapse and not let water flow freely, is there a good spring in the lower? Check both hoses at running temp and see if they are both warm/hot. If not the problem lies within the radiator or tstat, but since you ran it with no tstat, i doubt that is the prob. It is possible that the new motor had a ton of junk in it and clogged your new radiator. Flush it out.

I dont think your water pump is the culprit. Is the jeep leaking coolant from anywhere?

Are you losing coolant at all mysteriously? Maybe bad head gasket if so.

Do you have the right radiator cap on, i think 13 psi is what is called for, not 100% on that tho.

Do you have a fan shroud? That helps with cooling also.

 

Yea I've replaced all hoses. The coolant is very clean, along with what I can see in the block. I flushed it very well when I first put the motor in. I have never lost coolant through all of this. The cap is new as well @ 16 psi. I'm sure thats higher than stock, but won't hurt anything. It doesn't have a shroud, but niether does my 95 xj and it has no issues. I know a shroud will help, I just don't think its the problem. I also turned the electric fan on constant. This is my 5 th jeep ( all xj or mj) and I've had problems with some of them, but they were easy to diagnose and fix.
Has anyone had problems removing air from the system? I did the old park on an incline and warm up / cool down while topping off thing. Its always worked before.

 

Jeeps don't have reverse flow pumps on some models do they ( like chevys and others)?

 

The open system will purge the air out itself over a couple warm up cooldown cycles.