My 95 XJ is heating just below the red zone on long drives, when I turn on my heater it actually brings it back down to the mid normal temperature. I'm confused on what may be causing it. Previous owner just installed a new water pump, new thermostat. Everything works great otherwise, I do get AC and Heat works perfectly fine. Just not crazy about having to drive home in 90 degree heat with the heater on to keep the car cooled down. Maybe the electric fan is messed up and only coming on when I run the heater? It's a head scratcher.

 

If the heater core starts cooling it down when you turn it on, then that says adding extra surface area is needed.
So I would think your radiator needs to be flushed at the very minimum.
Did the PO flush the cooling system when they did the other work?

Also checking the E fan is an easy thing to do if your AC is working.
Maybe open up your hood and do some trouble shooting?
You know there are no less than 1 million threads on this subject?

 

Your radiator is probably clogged...when you turn on the heat...the heater core becomes your new radiator. ...turn on any ac mode...does the aux fan come on...the compressor must engage to turn on the fan. Pull the connector off the thermostat sensor with the engine running..the fan should come on. Do you have an obd 2 code reader. Check your coolant temp when hot..the fan should turn on by 220 ish...early 96 should have the temp gauge running off a temp sensor at the back of the block drivers side..later models run off the sensor in the thermostat. Easy to figure out...run eng for 10 min..disconnect sensor on the thermostat if it goes to cold...no sensor at back of block if it stays warm or hot then secondary sensor...might be bad and temp is really not that hot...i just saw your a 95... should have the sensor at back of head...if its accurate your fan should have turned on long ago..dont think a 95 is obd 2 so forget that...might need a temp gun to check temps at the thermostat housing to confirm

 

I am aware of that considering I've browsed the forum for ages before making an account, but after SEARCHING on google AND this forums search feature, and OTHER CHEROKEE forums, I was not able to find this exact instance of running the heater cooling down an engine, my apologies. I will definitely try and see what's happening troubleshooting wise. I will definitely look into getting a rad flush, I was really thinking it'd be the radiator causing most of the issue to begin with if the Water pump was replaced with a mopar pump, thermostat etc.

 

On long drives you say?

First: Do you have anything blocking the radiator? Like a winch? I put a winch cover on mine and went up 20 degrees on the highway.

Next, pressure test the system. You can rent a tester from most parts stores. Don't forget to test (or just replace) the cap.

I'm suspicious that it might possibly be a head gasket on the early stages of failure, but let's not jump that far yet.

 

I have nothing blocking the radiator except for a tranny cooler. I don't think it's a head gasket as I'm not losing any fluids, and my coolant/oil looks clean with no wierd looking additives of oil or coolant in either. Also not blowing any odd smoke or dripping water out the exhaust excessively.

The electric fan DOES kick on by itself when the car heats up, I just don't understand how I can drop so much heat by turning the heater on and it drives perfectly fine on the guage in the middle where it needs to be. The clutch fan is still good and has some resistance to it, doesn't move back and forth indicating a messed up waterpump or any issues with the clutch bearing. Definitely no leaks from the water pump itself or any hoses. Wonder if maybe the heater control valve is messed up because I am noticing near the seams there's a small bit of dried coolant there on the plastic, but not sure how that'd effect anything considering when I park it there's no drips or anything relating to coolant.

I just replaced the rad cap with a 16lb cap from Napa as well, since the previous owner stuck a 13lb with a release valve on it and I figured it was failing already.

 

Turning the heat on adds another heat sink to the system. Sometimes it's just enough to cool.

Using the heater doesn't require the thermostat to be open, BTW.

Highway speed overheating is often a blown head gasket. Don't rule it out.

Also, new parts does not mean good parts.

 

I think its pretty straight forward this and how to approach the issue at hand. Nothing weird about it.

And for what it's worth: the OEM thermostat is one of the very few parts that I'd get from the dealer's..