90Limited

Hello everyone, please excuse me if I am posting this in the wrong section, it is my first post here.

I have a 1990 Cherokee with a 4.0L and I have recently done the conversion from the problematic renix closed cooling system to the 91+ style cooling system after many plastic bottles and caps failing. My parts list included a new spectra radiator, new 195 degree stant thermostat, and a universal overflow bottle from napa. I also deleted the heater control valve and ran the hoses directly into the heater core.

The new system cools very well, however, I have noticed an increase in coolant pressure in the upper radiator hose. The hose is also new. The pressure is high enough that the hose is firm when the jeep is at operating temperature and some coolant is being squeezed out between the thermostat housing and gasket and the head.

This jeep has had a history of running hot, however it still runs very well and has only 121K on it.

I have heard a possible cause of the high pressure can be a cracked head or blown head gasket however, I have noticed no coolant in the oil, oil in the coolant, or white smoke from the tailpipe. There are no bubbles in the coolant while the jeep is running. I am also running a 13 lb brand new napa radiator cap.

I will be doing a compression test on it next week at school, however I would love for someone to share some knowledge on what else could be causing this issue, or if the pressure is completely normal.

cruiser54

The pressure is not causing the leak at the thermostat housing.
The leak is allowing the coolant to get hotter since there's not enough pressure on the system due to the leak.

Fix the leak.

90Limited

Thanks a lot! I used permatex black gasket maker with the gasket when I installed the housing. I'll be trying it without any rtv and will hopefully get a better seal.

cruiser54

Gasket with GasgaCinch or Indian Head gasket shellac. stay away from RTV.

90Limited

Will do! thanks.

Jakers

You've mentioned this to me before as well, I'm curious if you use RTV (red/yellow/black/grey) with any gaskets or if you just stick with GasgaCinch/Indian head gasket?

Jakers

Did you get the leak fixed?

cruiser54

I only use RTV where no gasket is used.

Black for engines. Gray for diffs.