87 comanche runs hot

Asked by Sep 04, 2010 at 10:24 PM about the 1987 Jeep Comanche

Question type: Maintenance & Repair

87 Comanche runs hotter than normal. Boils over when turned off.  Running at about 230 with thermostat, and 200 without.
New radiator, new waterpump, new hoses, new thermostat, and therm opens at about 185. Question. is there two different pumps?, each turning a seperate direction. One for a serpentine belt, the other for v belt?

9 Answers


I have 87 mj same trouble as yours after I changed everything I got it to run between 190 and 220 but it will hit 230 if I run it hard. Didn't know if it had something to do with the rust in the moter cause everything was rusted bad especally the radator.

1 people found this helpful.

After checking everything, I'm prone to believe it's the water pump on my Comanche that's causing the problem. Pinching the top hose (with therm removed) while running, I feel no rush of water when turned loose. Taking the top hose loose, there's minimal flow coming from the water pump. New pump, but I've seen bad one's before right off the shelf. Running without a thermostat, it runs at an average temp of about 150, but that's with constant flow. Both fans are working properly. Block's clean with good flow, new everything else. Hose configuration is correct as to the manual. I'm going to try another pump.

Picture of my 87 Comanche with a Ramsey 9000 winch.


I just changed water pump again assuming it was bad from shelf but when I touched radiator it had cool spots in different fins could new radiator be bad? How do you post pictures of comanche I can't get it to upload

I posted my picture by clicking on browse, the going to my pictures for the picture.

my 87 comanch 2.5 required a fan clutch last year...that fixes the problem. jc in NJ


Overheating problems have plagued the Comanche and Cherokees since day one until Chrysler completely redesigned the system. You probably have the infamous "open cooling circuit" which is actually a closed circuit. Look to the left rear of the engine compartment and see if you have a large white tank with a screw top and a bunch of hoses coming out the bottom. If so, you have the open circuit and the best thing to do is to change it to a "real" cooling system.It is a nuisance and will require a new radiator (visit a salvage yard) but will help quite a bit. Check to make sure your electric fan comes on when it is supposed to and consider getting an electric fan to replace the mechanical one. There are also "high volume" thermostat housings which actually do improve coolant flow. You are using at least 50/50 anti-freeze and good water, right? Fortunately, insturctions on how to do all this stuff are easily found on the web.

4 people found this helpful.

I run an additional electric fan that is manually controlled, so when driving at lower speeds like offroading I flip the switch and it keeps the jeep happy

I have a few Jeeps with the 4.0. They all run hot, jeeps like to run from 205 to 230. This is normal operating temp for jeeps. I have the open cooling system it never fails me yet. make sure you bleed the air out of the system and you fan clutch is working. If your worried about over heating you can use a product called water wetter. Then use 70 water 30 coolant. I run 50/50 with o problems. when I am off roading in low 4 x4 mode she stays about 225. Also don't forget renix jeeps don't have great gauges, I replaced mine with after maket gauges and I see the factory ones off as much as 15%.

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