So the other day I took my XJ on the highway for the first time in months. It drove smooth but it came dangerously close to overheating . ( the line before red; I consider that overheating). Anyways, I got it to my girlfriends, parked it and let it cool down. Checked the coolant and it was fine. Then drove it the same route home with no issues. My guess is fan clutch or maybe a sticking thermostat? Note: My jeep also has hood vents and the e-fan is on a toggle switch and was running the whole time. Thanks for the help.

 

Best way to know is using an infrared thermometer to verify if your temperature sensor is reading accurately. If the car showed no other signs of overheating other than the dash gauge reading, it's not necessarily anything other than a sensor problem without more conclusive data.

 

that is true...but causes could be a bad temp...if thats the case. easy replace.

 

I had a problem like that and mine was simple. The connector to my knock sensor came off causing the timing to be advanced all the time causing the truck to heat up quickly and continue heating. So just as a quick check I'd look at that. If you don't know where it's at check autozone.com for your jeep. On mine it was on the driver side of the engine block right above the oil pan.

 

XJs have a knock sensor? I've read that a running efan at highway speed can impede air flow thru the rad. No fan(s) should be needed at highway speed.

 

Yup well at least on the Renix they do. Here I got this info for ya.

OPERATION



The knock sensor is located on the lower left side of the cylinder block, just above the oil pan. The knock sensor provides and input to the ECU that indicates detonation (knock) during engine operation. When detonation occurs, the ECU retards the ignition timing advance to eliminate the detonation at the applicable cylinder.
TESTING



This procedure requires the use of a special tool M.S.1700, or an equivalent knock sensor tester.

1. Connect diagnostic tester M.S.1700, or equivalent, to the vehicle according to the manufacturer's instructions.
2. Proceed to state display mode.
3. Start the engine.
4. Observe and note the knock unit value.
5. Using the tip of a screwdriver or a small hammer, gently tap on the cylinder block near the knock sensor and watch the knock value. The knock value should increase while tapping on the block.
6. If the knock value does not increase while tapping on the block, check the sensor connector. If the connection is good, replace the knock sensor.

I tried to find a pic but no luck. I will continue to search. take care.

 

So a knock sensor would be a non-issue to the OP with a '91 non-Renix XJ?

 

hey man took my jeep into the shop yesterday for the whole cooling system to be redone....well it looks like i got a call today and its going to come out $1400 for everything on my cooling system nothing at all worked. they said they dont even know how it didnt blow up. no water pump worked no t stat. leaks all to hell...
i guess thats what happens when you buy a $500 xj
im in High school so i gota take on 2 jobs to pay that off.

 

Thanks for the quick replys everyone! I do have a 91 XJ, and I don't always have the fan on while im on the highway but i was too scared to turn it off when it was running hot like that! Lol. Also i forgot to mention it started to cool down once I got off the highway. That's why I was leading towards a fan clutch... But either way I haven't got a chance to get it out yet (busy@work/ def not my dd) but I appreciate the pointers; that's what makes jeepin what it is

 

brother if i were you i's do that s**t myself. if you don't know how well you did only pay $500 for it. and besides you can always get on autozone.com and look at the repair manuals there. they are the online versions of the haynes manuals. just saying. i know time may be an issue but..........

 

its all i could do i needed it fixed asap and i wish i had the time but i didnt have the time

 

i fully understand bro. well hopefully everything works out for ya.

 

yeah me to for what i put into it if one drop of coolent hits the ground ima go nuts and that ac better be the coldest thing in the world lol