I've got a 92 Cherokee Laredo with almost 225k on it. I've just recently replaced the rear main seal, timing chain cover seal, valve cover gasket, and oil pan gasket. This is the first summer I've had it out in Memphis since purchasing it in Alabama last October. To my question-
When I turn on the AC or idle the xj without the AC the water temperature goes up pretty quickly at the same time as the oil pressure decreases just as fast. The oil level is good, the water level is good both in the reservoir and the radiator... as long as I keep the AC off and don't sit at idle too long she runs pretty good. I'm wondering what might be causing this?

My thoughts we're the oil pump but I've been told my symptoms would drastically get worse if that were the case. And also I believe my head gasket is leaking as well, but I didn't think that would cause it as long as I keep my oil level good.

 

Correct me if i'm wrong but do you have the CLOSED cooling system? If you do here's the issues, those work great when there new. But get some miles on them they just don't cut it. There is a couple of things you can do, One is a basic Rad flush and new thermostat, the other is to swap out your rad system for a 93 it is a dirrect swap except it will eliminate your pressure bottle and all the plumbing that goes with it. The new rad will have a cap making it an OPEN system, you will have to install an over flow bottle. As for the heater hoses the one coming off the water pump goes into the top heater core piping the bottom goes into the thermostat housing just run straight hose. For the issue with your fan switch there is two things that can be done either get a thermostat housing out of a 93 and locate a temp switch for it, or do what i'm doing. The big wiring harness that runs down by the air box has a plug coming out of it right near the nose, this is the harness going to your fan switch located in the rad, if your unplug that and install a jumper your electric fan will run any time the ignition is on, or you can install a dash switch through that harness and control it your self, but don't forget to turn it on. I am planning on doing this swap in the next week and a half and when done I will post swap with pics, because here in Phoenix my closed system just is not cutting it. I just pulled my thermostat to get me through the week until I get the money for the parts, I know this isn't the proper way of fixing things and it will kill my fuel economy but its a Jeep, sometimes you have to do things to get them done.