89 XJ goofy cooling problem, please advise....

[cherokee4fun]

Howdy,
I have a 4.0 1989 Renix XJ that has been giving me concern over it's cooling system. Since I have had this one, it has always run cool, like 140 degrees, and the electric fan works when I turn on the AC, so I know it works. However, if I sit at a drive up at afast food place, it will start to heat up way over the 210 that I expect it to, and the fan does not kick on. If I start to drive, it cools way down fairly fast to the 140 area. I assume that the problem is the switch in the radiator, that sensor for temp. My guess is that the relay works, since the electric fan comes on when the ac compressor kicks in. I was also thinking that the mechanical fan might be a issue? Before I tear into this, I thought I would ask those that are more experienced than me!!! I am starting to think the fact that the xj runs cold, that it might be more involved than just the thermo switch in the radiator.
Thanks and your advice is greatly appreciated
Bob

 

[XJOwner95]

they actually usually have over heating problems, i have an 88 but i got mine dialed in pretty good, never gets over 210 and that its normal op. temp...but it does sound like ur temperature sensor is bad...cus my electric one turns on right at 210...my book i have says run to jumper cables to it and if it turns on but doesnt turn on over 210 then its the temp sens.

 

[mongolchuck]

The running cool part could be a stuck open or weak thermostat. But the running warm part sounds like too little airflow across the rad like was mentioned. Typically, the belt driven fan should be pulling sufficient air, especially during the winter. Check your condensor and rad for being clogged up with bugs, grass and dirt. Maybe its just clogged up on the side with the mech fan so when you start getting air flow across the other side, like when driving, it cools down. Just typing my long rambling thoughts.

 

[slimpartywagon]

I am having same problem with my 89... but my electric fan comes on when the temp gets above 212... heater blows cold-luke warm air at best.

 

[Saudade]

Assuming 140 is accurate, I'd agree the thermostat may be stuck open. Your temp should not drop this low.

Next, the radiator fan switch is located in the driver side rad tank, just below the trans cooler line. The harness should go under the airbox to a connector. Disconnect it. With the key on, jump the connections on the main harness side, the fan should turn on. If so, it's likely the switch.