Need Help Please..99 XJ intermitted Overheating.

Hello all,

My 99 xj is overheating intermittedly, the temp gauge goes to like 230 or more for awhile then goes back to like 210 or 215. It does not do it all the time it just happens at the craziest times, it could be on the highway or just pulling into the driveway. I checked and both fans are running when it happens, so I strongly don't think it has to due with the electric fan or any of it sensors or relays they seem to be working just fine.

1) I flushed the system twice. (no help)
2) Replaced the fan Relay. (the electric fan is kicking on at 210).
3) With both fan running it still overheats.
4) I do not think it is a air bubble because I flushed the system twice
5) The thermistat was changed last year.


The jeep is 8 years old this month with 120,000. I am the original owner so I know that it is the original raditor and orginal water pump.

Could it be the Fan clutch?? Would that cause intermitted overheating at fluke times and then cool down for no reason and then overheat again.

I am totally stumped if anyone could give any advice I would really appreciated it. I don't want to replace things that are working fine and still not fix it.

Thanks

Jeff S :huh:

The clutch fan could definitely have something to do with it. It could be getting weak? Or maybe the sensor for the electric fan? Mine overheated when I had the AC on or no AC but on defrost cause my Electric fan wasn't turning on, and the clutch fan couldn't keep up

If it overheats at speed then it's probably not a fan issue.

On my old one, the temp guage consistantly ran near the red line. I pulled my hair out over it, got a 3 row radiator, a new water pump, tested my thermostat in a pot of hot water. Finally i got a meat thermometer and actually measured the coolant temp and it was right around normal. I chalked it up to a bad guage or sender. ymmv.

A bad headgasket can cause overheating. There are two ways to test this. One is to get a cooling system pressure tester and pump it up to make sure it holds pressure. This is a good idea anyway, if your system doesn't hold pressure your engine will overheat. The other is to get an exhaust gas tester, it's like some chemical strips or something you hold near the radiator neck to see if there's exhaust gasses getting into your cooling system. Best to do both tests really.

You can test your thermostat by putting it in hot water with a thermometer and verifying that it opens at the correct temperature.

A bad radiator cap will not hold 15psi like it's supposed to and will allow the water in the head to boil thus causing overheating. Buy a new radiator cap and make sure that the lips where the rubber seals sit in the neck are clean of gunk and rust. I had this issue on mine recently and it would periodically barf a cup of coolant on the ground and the expansion tank would always be empty when cold and overflowing when hot. Cleaning the gunk out of the neck and the cap and oiling the rubber gaskets seemed to fix it although I'll probably get a new cap anyway next time I'm at the store.

Thanks for the replies, I bought a new cap last year, but maybe a new one could not hurt. I think I am going to change the clutch fan for the heck of it. I am at a loss. I also look into having those tests done.

Thanks

does anyone else have any ideas
Jeff

A new cap wouldn't hurt, and it's a cheap part....I got mine for about $10 from Napa about a year ago when I noticed my coolant level getting very high in the overflow bottle after it warmed up. Put a new cap on and it eventually settled back down to normal levels.

I would also definitely check into making sure the guage is actually telling you the proper temp.

Is it really overheating and cooling? Or could it be the gauge that is going bad? That isthe only other thing that I can think of.

Thanks for the reply, I could not say if it is really overheating, the check engine light goes on and a chime goes off, when I check the temperature guage it is in the red zone then after a while it goes back to normal temperature. It is very strange. I can not figure this one out. Would anyone suggest since it is summer time I remove the thermestat to see it that stops the problem.

Jeff

My 92 has similar issues, yet I have tested everything and found everything working fine. Mine doesn't do it when the AC is on though, and it really does overheat, however there seems to be no ryhm or reason to it.
I am to the point I am thinking two things could be causing it. 1: a bad O2 sensor thats loosing ground and causing a lean condition and then overheating 2: something thats loose in a water jacket causing the odd overheating.
We once found a chunk of rust in a race motor that would occasionally block a water passage in a head and cause the motor to over heat then the next race it would be fine....talk about strange!

JS

Thanks JS4309, It has not happened today so far, I think I am going to the dealer and buy a temp sender and replace it.

Jeff

Buy a $5 meat thermometer and verify that the sender is bad before you throw away money at the stealer for a new one. For like $20 at walmart you can get a nice digital one with a remote probe you can also use for barbecuing

230 really isn't overheating, just warmer.

Overheating = the "redzone of death"

I really thought mine was a bad guage, but it does boil, just not consistantly. Yesterday it was right about 70 and it didn't overheat, today at 62 and half the time in the same drivethrough it overheated, that tells me there is an intermittent blockage somewhere.....oh what fun!

JS

Is there scale in the radiator? Do you have a leak, the fluid in the overflow bottle will evaporate, but you should NOT loose more than a pint in a year, if its dropping faster than that, you must have a leak.

You did add anti-freeze, correct?

Flushing the system doesn't remove air bubbles, after you flush you still have to drain the system and re-fill it with new coolant. Any time you add fluid when air is in the system it can get trapped and form an air bubble.

Is this a closed or open system? If open, is the coolant recovery working? With the system cool, open the pressure cap and make sure the coolant is at the tippy top right up to where the pressure cap seals. If there is any air in the radiator the coolant recovery isn't working and perhaps the air in the system is circulating and sometimes forms a buble to cause the spike in temp.

I've been having a problem lately....temp will get warmer than normal around town (mind you it's only bee 60-70 degrees) and on the highway. Yesterday I did alot of highway driving and the temps were warm....I'm guessing it's the temp gauge, or brand new Thermostat I put in back in December. Although the upper hose is hot so I don't think there's a serious flow problem!

It got up into the redzone once so I pulled over....Coolant level was not elevated. Second time it happened it went up to 230 or so. I popped the hood to let more airflow in but it didn't help. It just stayed at 230 until I got to my destination.

If it were really into the redzone of death, wouldn't my coolant level be much higher in the resivoir due to the expansion of the coolant at that high temperature?

Sorry to hijack your thread but maybe our problems are related.

I replaced my heater valve last April 2006, radiator in July 06 + a coolant flush, water pump and radiator hoses October of 06 (along with a coolant flush then too), and thermostat + thermostat housing as of December 06...I didn't start to notice the increasing temps until March or so.

I did replace my coolant temp sensor with another used sensor I had lying around. Didn't help, so I'm guessing that sensor isn't to blame.....I'm betting it's the gauge sender at the back of the head, or the thermostat. Oxygen sensor is new as of March.

Well after doing a scan today I am thinking the problem I am having may just be the O2 sensor leaning out the motor and causing it to get hot. I scanned the thing 4 different times and was getting odd readings. When I first started it in the morning it suddenly had a miss which is why I scanned it in the first place. What I noticed with that scan was the O2 sensor switching back and forth between rich and lean and it did that for 30 miles. Temps stayed normal. After I shut it off and went in the bank I get back in start it up and it ran normal, however the O2 sensor went lean and stayed there 18 miles later I was going through a town at 30mph and it bgan over heating. Then after I was done working there (2 hours) I get in and drive to the next job 13 miles away, and it didn't over heat. the O2 sensor switched back and forth between rich, center and lean.
So it appears to me the issue is either the O2 sensor or the computer

JS