i have a a 97 XJ 4.0 4x4 auto trans and have been dealing with an over heating issue with the A/C on fore most of the summer. I had replaced the water pump, thermostat(195 degree), fan clutch, electric aux cooling fan , ECT radiator (CSF all metal 2 core ) and muffler( restricted and causing poor performance). After replacing the muffler all seemed well until one particularly warm day of extended driving i was on the interstate running 65 mph and the coolant was running just under 220 when it spiked up to 240 and the "check gauges " warning light came on. I killed the A/C threw it to high heat and it cooled back down to under 220 in a couple of minutes. I started using the A/c again and noticed that the engine ran cooler in traffic around town than when running on the interstate in clear traffic.here lately it has started to indicate overheating but the temp gauge would flash to a high reading and return back to where is was reading or swing to full cold.. I replaced the Temp switch thinking it was faulty and the engine temp was not changing as quickly as the gauge indicates. I still have the car running hotter at interstate speeds than around town and the temp gauge still sweeps randomly but not as often since replacing the temp switch. I am thinking that maybe the radiator being a cooper core as opposed to aluminum may not be as efficient as the aluminum radiator and the extra core(passage) may be flowing too fast not having enough time to cool the coolant at the higher engine speeds. Additional information is the Jeep is on 31s and I do have a winch installed.

 

Have you verified that the aux fan is turning on at 215-218F or anytime you turn on the AC? What's the part number for the fan clutch you replaced? Maybe you were given a fan clutch for a 4 instead of a 6 cylinder. Is there an air pocket, have you noticed a coolant level drop?

 

Aux cooling fan comes on with a/c running and the fan does come on with the a/c off . i have not checked at what temp, but it does not run hot when i am NOT using the a/c. I would need to check the part number for the fan, but visually there were identical. I know that is not always a guarantee that the parts are correct.. I have no coolant loss and all but sure I have bled the system completely.

 

What's the condition of the a/c condenser?

 

The A/C cools fine so I'm guessing there is no damage to the condenser.

 

You need to ensure that your torque convertor lock-up clutch is operating properly. If it is not locking up at high speeds, the transmission fluid will get very hot, and it runs through radiator for cooling, which can present as high coolant temperature.

To test:

1. Cruise at steady 55+ speed on flat surface and note engine RPM
2. Tap brake pedal lightly with other foot (just enough to activate brake switch/lights)
3. Engine RPM should jump quickly up by about 300 RPM
4. After about 3 seconds the engine RPM will drop back down to the original RPM noted in #1

If the lock up clutch is not activating or otherwise not operating properly it can leave the entire power train depending on the fluid coupling of the torque convertor which at high speeds can get very hot.

 

I was thinking more in terms of the condenser being fins clogged. If they are the heat that develops from the a/c being run can't be dissipated so your vehicles cooling system will have to deal with that increased heat.

 

Wouldn't the fins clogging up cause a situation where the radiator itself wouldn't get sufficient air flow (being that the condenser is in front of the radiator) and cause the problem regardless of the A/C?

I think it's probably worthwhile to check BOTH the condenser for obstruction/damage as well as the torque converter test that Jordan mentioned.

 

I definitely agree that both need checked.

Maybe it depends on how blocked it is as to whether it would affect the radiator when the a/c isn't on. I know that with the a/c running that condenser gets very hot compared to when the a/c isn't running. Also more heat is developed if the a/c compressor isn't in the best of condition even though it's working.

 

I'm wondering if there's an issue with the actual gauge itself. The 97+ gauge clusters are known to get corrosion at the connector.

 

Definitely lots of things to check. I'd like to know what an inferred guns shows to.

 

I gave this test a try and the RPM jumped up as described but was like 1-2 seconds, not very long before it returned to the original RPM. Does this indicate the TC lockup is not working or is 3 seconds a variable time not to be exceeded?

Thanks again for the help