Overheating issue/tried several things...

[joe_peters]

Fan clutches are weird ducks. Normal operation is coasting at 20~30 percent of shaft speed, when engaged they run at 60~70 percent of shaft speed.

When cold, like overnight, the silicone fluid seeps out of the reservoir. When you start the engine in the morning the clutch will engage until it spins the silicone fluid back into the reservoir where it is held by a valve. When the temperature of the air flowing through the radiator hits 170 degrees (coolant temp will be about 30 degrees higher) the bi-metal spring on the front of the clutch expands and opens the valve allowing the silicone fluid to cause the clutch to engage.

Can you test a fan clutch? Yes, in fact the procedure is in the FSM.

The life span of a fan clutch is about the same as that of a water pump, 4~5 years. With the engine cold and OFF, try and wiggle the fan side to side to check for loose bearings on the shaft. Give the fan a little spin and feel the resistance, it should feel a little stiff. Start the engine and let it run for about 5 minutes. Shut off the engine and spin the fan. It should spin easier because the silicone fluid is back in the reservoir. Then restart the engine and let it come up to full operating temperature. Shut off the engine. Try and spin the fan. It should be stiffer as it should now be locked up enough to spin at the prescribed 60~70 percent of shaft speed.

 

[jmeti000]

When i first got my cherokee, it did the same thing, and i had no heat either. Instead of spending a whole bunch of money on all those flushes, go to your nearest grocery store and get a pint of white distilled vinegar, and after draining your cooling system pour in the vinegar with water and fill it back up. run the engine so it can circulate with your heater on high, and then let it sit for a while (i let mine sit overnight). after its sat, redrain it, and flush it out really good. you can backflush your heater core too by just unhooking the hoses and flushing water though them one at a time. It was amazing to see all the junk that came out. havent had a problem since. one thing to watch out for though, is if anything is severely rusted or corroded, the vinegar will eat through it, and cause it to leak....but at least then you know if you need to replace something.

 

[joe_peters]

When i first got my cherokee, it did the same thing, and i had no heat either. Instead of spending a whole bunch of money on all those flushes, go to your nearest grocery store and get a pint of white distilled vinegar, and after draining your cooling system pour in the vinegar with water and fill it back up. run the engine so it can circulate with your heater on high, and then let it sit for a while (i let mine sit overnight). after its sat, redrain it, and flush it out really good. you can backflush your heater core too by just unhooking the hoses and flushing water though them one at a time. It was amazing to see all the junk that came out. havent had a problem since. one thing to watch out for though, is if anything is severely rusted or corroded, the vinegar will eat through it, and cause it to leak....but at least then you know if you need to replace something.

Not a bad procedure EXCEPT in PA in the winter.