Daughters XJ overheated yesterday and I'm trying to figure out why. Not sure if AUX fan is the problem or if thermostat stuck. Not leaning toward thermostat cause if it was stuck closed, I would think it would've run hot before she got to me.
Here's my questions:
If the AC is on, and the aux fan isn't running, is that enough to make it overheat while stopped in traffic for 10-15 minutes?
To 250 Degrees?
Back story below if needed.
99 2WD XJ with 178k on it, 4.0 and automatic.
Two months ago, replaced with radiator with a new one because the old one split down one side of the right hand tank dumping all the coolant.
When I replaced the radiator, I also replaced the water pump with a new one and thermostat as well. Old one wasn't leaking and flowed well, but the mounting tab for the power steering pump was broken off by PO and since I was in there already seemed an easy fix. I flushed the system and backflushed the heater core and the system seemed pretty clean. With the tank broken open on old radiator I could see into the core pretty well and they were surprisingly clean. Good sign. Refilled with appropriate coolant and drove on.
No issues for past two months. Yesterday as daughter was coming to see me at work, (35 miles of mixed highway and city) she got stuck in traffic and temps hit 250. When she got to me, it wasn't boiling over but when she stopped it did and started and pushing coolant out of overflow. AC was running. I used water to cool it down by pouring it over the radiator until it started sucking coolant back in from the overflow. Once cooled down a little, I pulled the cap and topped the radiator off again.
I reached down and grabbed the aux fan wiring harness connector (located below radiator fill cap on left side of jeep) and the fan kicked on for a few seconds, then stopped. (AC still on) grabbed it again and fan started and ran continuously the rest of the time. Poor connection maybe?
I'm thinking lack of airflow... probably caused by faulty fan connection.
Yea, sounds like the first place to start. I would check the connector and see if anything is loose / dirty. Clean up / fix / replace as necessary, and have her listen for the electric fan when the AC kicks on.
1992 Cherokee Laredo - all stock, DD. Needs some minor rust repair, then on to the mods!
I didn't get my AUX fan's connector reseated properly after removing it for better access once. Combined with my worn (but partially functional) mechanical clutch I experienced pretty much the exact same thing you're describing. Replace the Mech clutch (they're cheap and easy) then start it, turn on the AC and pop the hood. If the Aux fan isn't blowing good an strong when the AC is set to on then you've got a problem with the aux fan or its wiring.
"I just need to do a couple tweaks on my jeep, I'll be done in a couple hours." - gone 3 days