1991 4.0 running hotter then usual

I know this has been hashed over and over, but this one seems a little different.

I live in a valley, so everywhere I go is up hill and it's been relatively cool here lately (mid 80's). As I drive up hill at speeds of 25 - 35 mph, I can watch the temp. gauge climb almost as fast as the speedometer, it will quickly reach the red zone if I let it.

I didn't notice this trend until after I replaced the waterpump (the bearings/seal was going out of it). I've also noticed that the temp. rises at stop lights, but not always.

Is the rising temp related to the waterpump or could it be the clutch fan (I've flushed the radiator recently trying to fix this problem and it appeared to have great flow).

I've checked the clutch fan and compared it's resistance to the one on my pickup and it seems to be the same.

Any thoughts are very appreciated.

Brent

Check the resistance of the fan when its cold and when its hot, when hot it should be much harder to turn. If not replace it.

I'd still replace the mechanical fan clutch, they do wear out. Your comment about the temp rises at stop lights is what mades me draw this conclusion.

Once you do that and problem seems 90% solved then replace the thermostat with a new one from the dealer. Once you get a thermostat hot it can be damage. This would cause it to open later and close later. You will see bigger temp swings than before this problem started.

If you have 2 vehicles then pull the fan clutch off, remove the fan blades from the clutch, then take the clutch with you to the parts store. Some aftermarket "universal" clutches are just too tall and require tilting the radiator. I found one that was a copy of the AC Delco OEM unit I was replacing. Also with the mechanical fan you have to pull the shroud and fan out as a unit, you can not remove the shroud with the fan in place. You also have to install the fan and the shroud.

I took my fan cluch off and disconnected the spring. Istraightend out the crimp on the end and rebent it 3/16th inch closer to the end and put it back together. it now locks up at a much cooler temperature, It seems to be locked up good around town at 75 degrees and still unlocks ok out on the road. Richard

check the tightness of the belt around the water pump. i had a problem like that and the belt ended up waring out the bearings in the pully and it fried the pump. if the problem still consists after all this, try to cut a few slits in the hood and add a hood scoop to it facing twards the windsheild. a buddy of mine had to do that with his. oh, do you have the reserve elcetric fan?

I replace my fan clutch with one from autozone and my 89 xj still gets a little warmer at light and small hills. I've replaced my hole cooling system and that is the only thing thats not oem.

Essayons said:

Check the resistance of the fan when its cold and when its hot, when hot it should be much harder to turn. If not replace it.

Click to expand...

I checked it when it was up to temperature (210*), it actually had less resistance when hot than when it was cold. Based on your comment, this could be the culprit?

Thanks,

Bam

check for a cracked over flow bottle i have a 91 it was doing the same thing. though i had to replace the radiator, and over flow bottle.
got the GDI(radiator) from autozone, and a over flow from a junk yard for everything it was under $150.
good luck.

Legacy said:

check for a cracked over flow bottle i have a 91 it was doing the same thing. though i had to replace the radiator, and over flow bottle.
got the GDI(radiator) from autozone, and a over flow from a junk yard for everything it was under $150.
good luck.

Click to expand...

I should mention that my XJ has the factory "open" cooling system.

BAM

bam said:

I checked it when it was up to temperature (210*), it actually had less resistance when hot than when it was cold. Based on your comment, this could be the culprit?

Thanks,

Bam

Click to expand...

It fixed the same problem for me.

Hmmm --

The problem began after you replaced the water pump? Where did you get the replacement water pump and how confident are you that the seller knows anything?

The reason I ask is that the older AMC/Jeep 4.2L (258 cubic inch) engine was set up with conventional vee belts, not a serpentine belt like the XJ. The old style water pump will bolt onto a 4.0L engine, but the belt routing makes the 4.0L water pump rotate in the opposite direction than a vee belt engine.

If they sold you a water pump for a 4.2L with vee belts, the impeller blades are pitched backwards and you won't get much coolant flow.

Eagle,

I purchased it from a local shop (not dealership). I didn't release that this could be a problem so I didn't look at the impeller blades. But the pump did have the smooth serpentine roller on it. I haven't pulled it yet, I was assuming/hoping that it was correct.

BAM