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Overheating Issues

cb3725

NAXJA Forum User
Location
Cartersville, GA
Ok, I had a guy help me replace the head gasket on my 1990 Cherokee. We took the head it had it pressure tested and magnafluxed- all good. We finally finished yesterday and it is still overheating. It only idles for about 5-8 minutes before it passes 210 and keeps climbing until I shut it off around 250. No water in the oil or anything.

I've replaced the water pump and the thermostat (which there wasnt a t-stat in there when I opened it up. Previous owner must have removed it) and now have done the head work. What else could it be? I have no radiator cap- it's the pressurized system with the fill tank.

Also, even when it is running, that top hose feels empty, like no coolant is passing through it. Does that sound like my radiator might be bad? Or the heater control valve? Bad water pump?

If it is the radiator, I've seen some on here suggest going to the open system instead of the closed system I have now. How big of a deal it that to change?
 
Last edited:
Ok, I had a guy help me replace the head gasket on my 1990 Cherokee. We took the head it had it pressure tested and magnafluxed- all good. We finally finished yesterday and it is still overheating. It only idles for about 5-8 minutes before it passes 210 and keeps climbing until I shut it off around 250. No water in the oil or anything.

I've replaced the water pump and the thermostat (which there wasnt a t-stat in there when I opened it up. Previous owner must have removed it) and now have done the head work. What else could it be? I have no radiator cap- it's the pressurized system with the fill tank.

Also, even when it is running, that top hose feels empty, like no coolant is passing through it. Does that sound like my radiator might be bad? Or the heater control valve? Bad water pump?

If it is the radiator, I've seen some on here suggest going to the open system instead of the closed system I have now. How big of a deal it that to change?

You probably have air trapped in the system--closed systems are notorious for this.

BEST BET: Remove the thermostat and drill two small holes in the flange, far enough in from the outer edge so that when reinstalled the two holes will not be covered, placing the thermostat so that the holes are located at 12 and 6 o'clock. Fill the system. Park with a nose-down attitude, pull the temp gauge sender at the DS rear of the head, and then add coolant to the pressure bottle until all the air is out of the system. Reinstall the sender and test.
 
Make sure there are no cracks in the coolant tank, and the cap fits on tight. I went through this same problem after replacing the tank and cap, only to find the new cap was bad. Put my old cap on, and all is good! The upper hose should be hot, and hard (pressurized) after a few minutes of running.
 
I put a 1992 thermo housing with a sensor hole on my '90. I used a pipe bushing and pipe plug as a bleeder. works perfectly, cost $25. Just fill your system with the pipe plug out until you have coolant running out of the hole in the pipe bushing, then plug it. Also, drill the holes in the thermostat. No probs after that.
 
Did you use the correct direction water pump ? Next, how did you set your belt tension ?
Most who set it by hand set it to under 100lbs when it should be 170lbs for a used belt and 190lbs for a new belt.
 
Did you use the correct direction water pump ? Next, how did you set your belt tension ?
Most who set it by hand set it to under 100lbs when it should be 170lbs for a used belt and 190lbs for a new belt.

How can I tell if I have the right direction water pump? I dont have the original anymore to compare and just took the one the tech gave me from Advance Auto.
As for the belt, I did put it back on by hand and just tightened up the adjustment bolt until the belt wouldn't rotate more than about a quarter turn if you tried to twist it. I'm really not too sure how that goes in lbs though.
 
How can I tell if I have the right direction water pump? I dont have the original anymore to compare and just took the one the tech gave me from Advance Auto.
As for the belt, I did put it back on by hand and just tightened up the adjustment bolt until the belt wouldn't rotate more than about a quarter turn if you tried to twist it. I'm really not too sure how that goes in lbs though.

Quarter turn, you are around 60-80lbs, I actually have tested this with a krikit II tension gauge when this came up several times before. As for the correct pump, there should be an R either on the housing or on the impeller itself. Or take the part number to advance and pull another one and look.
Bleeding the system too is very important as well as the holes in the thermostat.
 
You probably have air trapped in the system--closed systems are notorious for this.

BEST BET: Remove the thermostat and drill two small holes in the flange, far enough in from the outer edge so that when reinstalled the two holes will not be covered, placing the thermostat so that the holes are located at 12 and 6 o'clock. Fill the system. Park with a nose-down attitude, pull the temp gauge sender at the DS rear of the head, and then add coolant to the pressure bottle until all the air is out of the system. Reinstall the sender and test.

That was it. Bled the air out today and the temp is back to normal. Thanks!
 
Quick follow up question, now that it is all back together and running smooth, there is a big difference in the normal operating temp. I used to run at around 210 all the time. Since November or so, it has never gone above 150-160. Could it be just the winter air is keeping it that much cooler?
It seems like a good thing considering my previous overheating problems, but I know some on here say it is important for efficiency that these engines run hotter.
 
Whats the status on your radiator. i changed the original one that came with my 1989 with a 3 row one from napa. It is night and day. My gauge just sits at 195. And it used to do what yours does.
 
That's no good. And it can't be THAT cold in GA. I wonder if the holes in the thermostat are letting too much coolant by. Do you remember how big you made them?

Yea, the weather really isnt that cold normally - high 20's this morning but its rare that it gets that cold.... When I put in the thermostat, I didn't even drill the weep holes in it and I have the original radiator. Ha, I guess I now have the complete opposite of my original problem when I started this thread.
 
Yea, the weather really isnt that cold normally - high 20's this morning but its rare that it gets that cold.... When I put in the thermostat, I didn't even drill the weep holes in it and I have the original radiator. Ha, I guess I now have the complete opposite of my original problem when I started this thread.

Did you put the right thermostat in? Needs to be 195*
 
Yea, the weather really isnt that cold normally - high 20's this morning but its rare that it gets that cold.... When I put in the thermostat, I didn't even drill the weep holes in it and I have the original radiator. Ha, I guess I now have the complete opposite of my original problem when I started this thread.

Your thermostat was a 195 degree?

If you have an efan, it could be running all the time.

Some fan clutches fail and lock-up, causing the mechanical fan to always be engaged.

At that low of a temperature your oil will have more contamination as the engine does not heat up and seal the rings as well, more blow-by, more condensation in the crankcase--the technical term for that is "bad Ju Ju".

Of course, your temperature gauge sender, gauge, or wiring could be at fault. After 20 minutes of operation can you shut off the engine and comfortable hold onto the upper radiator hose?
 
Have you overheated since that thermostat was installed? Default is locked open after an overheat.

Edit: I always install, and recommend, the Stant SuperStat Premium, 195 degree for the XJ.
 
Its policy in our shop to replace any thermostat that has been exposed to overheat. We have been using the NAPA superstats in most cars but do try to get Mopar thermostats for Chrysler products when we have time.
 
Your thermostat was a 195 degree?

If you have an efan, it could be running all the time.

Some fan clutches fail and lock-up, causing the mechanical fan to always be engaged.

At that low of a temperature your oil will have more contamination as the engine does not heat up and seal the rings as well, more blow-by, more condensation in the crankcase--the technical term for that is "bad Ju Ju".

Of course, your temperature gauge sender, gauge, or wiring could be at fault. After 20 minutes of operation can you shut off the engine and comfortable hold onto the upper radiator hose?

I checked and the efan wasnt running. After 15 minutes or so, the top radiator hose was warm, but definitely not too hot to hold.
 
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