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Overheating at idle

3

3XJFamily

NAXJA Forum User
Location
Austin TX
I've replaced everything (and the radiator twice) in the last few years trying to track down why this jeep wants to run hot. It was giving me problems in the summer and going away in the winter but now on a 70 degree day, we put a scanner on it.

It hit 220 at idle and climbing, and dropped quickly below 210 when the RPMs were brought to 1400 or so. The mechanical fan has resistance, and will pull a shop rag up to the grill at idle.

I'm thinking try a new fan clutch - which is best? If that doesn't work then I'm looking for a high-flow waterpump.
 
I'm with you on the fan clutch. Somewhere on here is a part number for a HD fan clutch for the 4.0, and I think it is available at Schucks online.
 
Make sure the cooling system is pressurizing. Radiator hose should be hard after the engine warms up. I had a new (and faulty) pressure cap on the expansion tank cause the problem you describe. Drove me nuts trying to figure out what was going on until I squeezed the top hose and noticed there was no pressure!

Just to clarify, mine would slowly overheat while idling, with the level in the tank rising until it finally boiled over. I have a 87 with the no cap on the radiator system.
 
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It's a 91 and this is the 2nd rad and cap - it's not overheating like a renix with a bad bottle. . .

A bad pump is the only other possibility I figure but, it went in new with the engine a few years ago and it's never cooled quite right so I figure it was doing it when the pump was new but, it's only a 45 min job to swap it anyway
 
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The 2 XJ's I have owned '94 and '96 would heat up at idle until the electric fan come on, even with all new parts;... that is everything except the fan blade itself.

?? Could it be the pan pully itself, the back of the belt have excessive slip over it?
 
If the standard fan clutch spins at 60-70% of shaft speed, then raising RPM=higher fan speed=more cooling.

Weak/failing fan clutch, lets say 30-40% of shaft speed, then raising RPM higher=higher fan speed=more cooling.
 
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