MT Ray

I sure hate to make my newbie post another overheating problem, but I have scoured this site and can't solve my problem. I've got a 98 XJ Limited; Box Stock; 4.0L; 110K; 2d Owner, purchased in 2004 w/55K. Never had a problem of any sort - best rig in the stable.
Month ago, it overheated on level highway; 70mph; outside temp approx 90deg. Pin hole in lower radiator hose cused minor coolant loss. Replaced both radiator & heater hoses. Temp gauge ran at 210deg, before overheating; now it runs at 220, then will suddenly spike to 250(1st red mark); then after about a minute, would drop back to 220. Did that a few times, now it sticks at 250, until the engine is shut off for a few minutes. Doesn't overheat from 220 when idling. Engine doesn't seem excessively hot, when stopped after the temp spike(no boiling or poping noises). Squeezing upper hose shows pressure in system. Pressure test was positive.
So far I have replaced: Radiator Cap
Both Radiator Hoses
Both Heater Hoses
Temperature Sensor
Thermostat (195deg)
Water Pump
Fan Clutch
Radiator Shroud
Serpentine Belt
Coolant (50/50)
I flushed the system & burped it 4X. The coolant is running clean, with no weird smells. Reference the temp sending unit supposedly located at the top rear of the engine - there's nothing there on mine. I don't know what else to try - only things left are the radiator & temp gauge. I sure need some help!!!! Again apologies for the long post and many thanks for letting me on board.

1976Mustang

Did you check the Aux fan? If it suddenly cools down it could just be the aux fan jamming or not coming on when it should. If that's the case, i don't know what controls the aux fan.

djb383

Have u replaced the radiator?.....the heart of the cooling system.

MT Ray

Checked the aux fan - seems ok - switches on at about 212deg. Will do some more checks, tomorrow, running on the road. Thanks for your help.

1976Mustang

Then yeah, replace the radiator and/or install Hood louvers if it's a constant issue.

MT Ray

Haven't replaced the radiator "yet". Any advice relative to an aftermarket radiator that will help with the problem? Thanks.

djb383

Just about any new OE style rad will way out perform an old clogged radiator.....+/-$110 at most auto parts stores.

dsapper

have you verified the temp with a second gauge? Also, sometimes an air bubble can form near your coolant temp sensor. With the vehicle running remove the temp sensor and let a bit of water burp out and reinstall it.

djb383

If u remove the coolant sensor with the motor running, you will have a major coolant mess everywhere and lots of air will then replace the lost system.

MT Ray

Latest Update - Been running variety of roads, hills, etc. Got a spike on the temp gauge, yesterday, to 250deg. IR therometer read 236deg. No spike since. Did a temp comparison w/IR thermometer, showng temp gauge in running high. 100=100; 127=105; 155=129; 182=150; 210=198; 222=216. Aux fan kicks on about 212 on the gauge and shuts off after a reasonable time. Temp gauge didn't get above 222, today. Maybe the problem is starting to improve. Or maybe the "gremlin" just fell off! I'm going to replace the radiator, just for my peace of mind, since that temp increase still bothers me. Will advise of any developments.
Many thanks to all for your advice, info & support. This a great forum!!

MT Ray

sthon

Hey Ray, I'm guessing you're from Montana? I'm originally from Missoula myself. Since you have a '98 you only have 1 temp sensor. It's located on the thermostat housing. On older I6's they have a second temp sending unit for the gauge located on the rear drivers side of the head. It sounds like your temp sensor isn't reading correctly, the aux fan should kick on at 218* and your IR gun readings differ from your gauge. I would suggest replacing the temp sensor along with your radiator.

MT Ray

You guessed right; I live in the Bitterroot Valley. I had planned to replace the thermostat(again) along with the radiator and I'll add the sensor to the list.
Thanks for your help. --MT Ray--

MT Ray

sthon: I see you're from CA. What part? I lived & worked in Sutter Co, before I migrated to MT in '95. Small World.
Regards, Ray