otimtyler

Before starting I’d like to apologize for the length of this post. It’s long but I wanted to try and get everything out there at once.

I'm hoping someone can help me with an overheating problem I'm having with my 1990 4.0 I6 Cherokee. I know overheating problems with this vintage car have been beat to death (I've spent days searching the internet) but I don't believe I’ve seen anything that addresses my problem. I’ll start with some history... I've had the truck for years ad have been plagued by the usual problems that always seem to occur on the way to Christmas dinner or to the airport. Over the years I've replaced the expansion bottle, cap, radiator, etc. so when it started overheating recently I decided I'd take care of it once and for all and convert the closed system to open. So what I've just finished doing is...
1. New 3 row all metal radiator with filler neck and 13 psi cap
2. New 195 degree thermostat and ‘92 housing
3. All new hoses (radiator and heater)
4. New '92 heater valve
5. New fan clutch
6. New Serpentine belt (correctly tensioned)
7. New water pump
8. Still waiting on the electric cooling fan switch but the fan is currently wired to come on with the ignition
9. New overflow bottle
10. Even added a transmission cooler while I had everything apart.
11. Before starting the repairs, the system was flushed, did he chemical Super Flush thing, and flushed it again. The fluid didn't appear to be "cruded up". After the repairs system was refilled to the bottom of the radiator neck with new 50/50 mix and overflow bottle was filled to full mark.

I would have thought that would take care of it but it still overheats. When started the temperature just keeps climbing until it gets close the "red zone" and I shut it down.

Things I checked after all parts were installed and I still had he problem:
1. There is plenty of heat coming out of the heater and the upper radiator hose gets warm (not to hot to hold but warm) so it appears that the new pump is working, and yes the belt was put on correctly so it's spinning in the right direction. I know because as much as I hate to admit it I got it backwards and when the truck still overheated on its first start up I went back and checked. Couldn't believe that I messed it up. Corrected the belt routing and tried it again. Made absolutely no difference at all. Acted exactly the same even spinning in the other direction.
2: here is a safely lever on the radiator cap and when the truck it hot and the lever is lifted pressure is released. Not as much as I would have expected, just a small sigh, but you can tell there is some pressure.
3. Don't see any coolant leaks, fluid is still up to the bottom of the filler neck and the overflow bottle level hasn’t changed at all.
4. Thought it might be an oil pump problem, but when cold pressure reads about 60 until it warms up. At that point it reads 38-40 at idle and 58-60 at higher revs. Seems high at idle to me but from what I've been reading this appears to be normal. So I'm thinking the pump is okay.
5. I suppose it could be the head gasket. I see white exhaust when cold, but after it warms up it's clear. This appears to be normal to me. Also don't see coolant on the dip stick, but the oil was just changed prior starting repairs so perhaps that's not a good indicator.

Actually this latest round of overheating started on the way home from the oil change. Not sure how that could have done anything. Receipt says they used 6 quarts of 5W-30 (starting winter here in New England), it has a new filter and although it's a little hard to tell because of the fresh oil, the dipstick looks like it is reading right on the mark.

Other than the cooling problem, the truck appears to be running fine. So anyone have any ideas? Did I miss something obvious or should I just bring it in for professional diagnosis? I know some will say I should have done that in the first place, but since I was contemplating doing the conversion anyway and had some time on my hands, for what it cost I thought I'd give it a shot.

Thanks.

littleredXJ

Are you sure it isn't an indicating problem? It sounds like the coolent system is sound, have you tried checking the temp with a source besides the dash guage? I would try measuring the actual temps of your radiator/head etc and make sure you don't just have a bad guage or temp probe

PingPong

I would take the jeep to a radiator specialist and have your cooling system Pressure checked. This will test your whole cooling system. It will pinpoint a headgasket leak or other kind of leak. Also what does you condensor fins look like, can you see through it? Is anything blocking airflow?

Is you mech fan working right? If you are idling and has no airflow then you will overheat.


I hope my advice helps.

PatriotGT

Remove the radiator cap (make sure it's cool first) crank it and watch to see
if bubbles appear in the water. If so, you have a bad headgasket(hopefully). Headgaskets can leak without affecting the oil. You can also do a compression test and pressure test as already mentioned.