89 Cherokee overheating...and overheating...

Okay...so we replaced the radiator, the heater valve, thermostat (twice - we now have the dealer one), the T-valve connector, the electric fan sensor...the water pump is good...we flushed the system...and yet we still overheat randomly. We are thinking (hoping) that maybe it is the heater core unit...we know that there is an air leak somewhere and that just before we overheat we lose hot air though the heater vents. There has also been a hissing sound that comes through the vents on the right side occassionally, but don't know what it is or if it's related. Any wisdom or advice would be much appreciated.

Make sure no air is trapped in the system and also get a new radiator cap.

Read this.... It works. The guy that I bought my Jeep from even installed a new engine trying to cure his overheating problem. The Jeep still did the same thing to him, he spent $4000 on new engine and trans, water pump, radiator, etc.. Discusted, he sold it to me cheep. My Jeep runs cool, and doesn't loose coolant.

Symptoms were the same as yours. When it started to boil all of the coolant in the expansion tank and heater core would turn to foam. No heater, and all of the foam would come out of the expansion tank cap and the head would fill with air.

Your problem is common and is the "Jeep Curse." This works!!!
http://www.automotiveforums.com/vbulletin/showthread.php?t=206558

I have a '91 and I don't have the closed system and my system has never been upgraded?

I have a '91 and I don't have the closed system and my system has never been upgraded?


They might have made a mid year change. Check the production date.

I pretty sure its Setember of '90. Im just glad I never have had to deal with the closed system.

Yeah, I had that problem, and it seemed like it would never end. Until... I heard about the easy swap to the later model cherokee cooling system. I ordered a radiator from I believe a 91 cherokee. Then I did the 1 hour radiator swap quick and easy. Chunked the pressure bottle in the trash and replaced it with an off the shelf coolant overflow bottle. I think I replaced a few old hoses, but basically that was it. I had a problem with the electric fan, the controler stopped controlling, so I wired it so that it is always on when the engine is on. No cooling problems since ( hint: make sure your t-stat is installed in right direction and fan is wired to pull air through radiator, not push).

The pressurized system just plain sucks, switch to the open system and never look back!