Wondering if someone can give me some advice,
I have a 1990 Jeep Cherokee 4.0 inline 6
I have not owned the Jeep very long but when I did buy it according to the owner and paper work it had a full radiator flush etc done at a garage. Driving it home on a constant climbing up a hill for like 20 mins it got warmer and warmer pretty much to the red!! Once crusing on the flat again it returned to normal! It also has had a new thermostat a year ago. Since then I have replaced the water pump and driven it round where it seems to stay at a constant temp until I go back to the same hill some time later and sure enough it heats up again!!! Baring in mind this is on the interstate and not a super steep gradient! where you can do 65 easy!!! Any ideas?? I am not familiar with Jeeps my first one in fact! My oil is clean so hoping it could be an air lock or hopefully some thing not too major causing this problem! Both cooling fans are also running fine! Any help would be much appreciated! Thanks

 

Could be clogged rad. Even though you flushed it. Mine was logged after i flushed it. New rad, no heat.

 

91 xj same issue a little over 2 years ago. I ended up having a small leak at the filler neck that was killing me. I didn't figure it out til it got real bad. Anyway, it was a pretty easy job if you are mechanically inclined at all. Out and in, radiator, thermostat, water pump and hoses. Been perfect ever since, even runs the coolest it ever has.

Hope this helps.