a different overheating problem

My overheating problem appears to be a little different. My 89 Jeep 4.0 will only overheat at idle for about 10 minutes. Driving down the road, its fine. I have noticed that my electric fan is not kicking on. Also, when it overheats, the resevoir will be full to the top with hot coolant. It only leaked once, and that was because the cap was loose. Any ideas?

You answered your own question. Fix your fan. Its either the relay, sender switch, wiring or the fan itself.

Yep. At idle there's not enough air or coolant flowing through the radiator. My fan kicks in all the time if I idle long enough.

Do you have A/C? If so, does the fan kick on when you turn the A/C on?

Nope, it doesn't kick on at all, is there a test I can do to see if I just need to replace the fan, or the relay or the switch? Or should I just replace all three?

There's a few things you can do.

Disconnect the fan from the harness and run some jumpers from a 12 volt source (the battery or a battery charger) to the fan and see it it works.

Connect a voltmeter to the harness end of the connection and see it you get any voltage with the A/C on.

You can also disconnect the connector for the temperature switch (on the radiator) and simply put a jumper across both terminals on the harness side. This should also send voltage to the fan connector.

I have the same problem, haven't fixed it yet. I find that if (not moving)I am idling, I get very hot. If I rev it up, I can watch it cool down. I think (besides the fact that my elect fan is not turning on to help)that my clutch for my mechanical fan is not tight enough at idle to have the fan spin enough.

after you figure out what is wrong with the fan and get that working (hopefully this is your problem) you should go to ebay and search for "cherokee cooling mod" You will find someone selling a small kit that allows you to run the fan manually by a switch in the cab or let it come on as usuall. It comes with factory type plugs that fit into (between) factory harness plugs.

It sounds like you have 2 problems. First, I would replace your mechanical fan clutch, when it heats up, engine off does the Mech. fan turn easy? If so its toast. Saudade told you else to do. Godd luck.

Make sure you coolant level is correct when the car is cold. Yours (and my '88) uses a closed system with a pressurized return bottle. If there's any air trapped, you'll never get enough coolant in the radiator to get the electric fan to turn on. It's tough to purge the air out. There are many threads already in here with advice and even conversions to an open system.

It sounds like you have 2 problems. First, I would replace your mechanical fan clutch, when it heats up, engine off does the Mech. fan turn easy? If so its toast. Saudade told you else to do. Godd luck.

Tried that, the fan is difficult to move when the engine is hot, so I guess it is the electrical fan.