GreenManXJ

I tried searching and couldn't find anyone with quite the same problem as I'm having. During a long highway trip a few weeks back while pulling a long hill my temp gauge went up into the red. I was just about at the top so I coasted down the backside, the temp dropped and all was fine. On the same trip while idling at a drive thru it did it again. I parked, turned it off and it was boiling over. It seemed like a sticking thermostat, I wanted to do a bunch of maintainance anyway since I recently bought it and don't know the history so I replaced the t-stat, water pump, and upper and lower hoses. Everything seemed fine but it's doing it again.

Here's the scenerio, while pulling a hill on a highway at about 3k rpm for an extended time it will be fine, then in the span of litteraly maybe 3 seconds it jumps like 30° and into the red. Once I'm on the flat or a downhill it will hold there for a little, then drop back down just as fast. I've never seen a temp gauge move that fast. Even if coolant completely stopped flowing for whatever reason I don't think it would rise that fast. It should be getting plenty of air thru the rad at 65 mph and temps were only in the 80's Any thoughts? I was going to try parking on an incline and burping again in case there is still air in the system but after that I"m about out of ideas.... I thought it possible the temp sender was acting up but since it boiled over once I know for sure it overheated and I can usually smell it when it acts up while driving... thanks in advance!

RTorrez1

The main cause for overheating while at idle or lower speeds (climbing a steep grade) is a bad or weak fan clutch.

IJM

What's the best way to test this? I think mine works fine, but I'll be doing some cooling system maintenance soon and wanted to be sure it was working fine.

It seems to have good resistance when I spin it by hand with the engine off, and it blows air pretty well at idle.

Pelican

OP, your model year and engine please? XJs are not even close to being the same. An example is the need and method for "burping".

RTorrez1

There is no 100% way to check them unless it's really on it's last leg. But, When it at normal operating temp it should have a lot of resistance. cold it should have less resistance. If it hasn't been change in the last 5-10 years it's a good idea to replace it.

GreenManXJ

Sorry I should have given a little more info. I have a '97 XJ with the 4.0 and 220k on it. I tried parking it on an incline last night, opening the rad cap and running it to see if I could get anything else out but I didn't see any more air. If it gradually overheated on a hot day while wheeling or something I would look at the fan clutch probably but like I said in my first post the needle shoots up like 30° or 40° in a matter of only a couple seconds... and this is while I'm doing 65.

The other strange thing is that the problem is intermitent. I drove it around yesterday when it was hot out without any issues.

I'll try to snap a couple pictures of my rig here soon and do a proper introduction.

Epk5150

Sounds like an electrical problem to me. Look at your temp senors and the associated wiring for any signs of damage. Search around for coolant temp sensor troubleshooting, there is a lot of info out there. Usually when a gauge is faulty these are the types of symptons you will have.

GreenManXJ

I would agree, my first thought was that the sensor was acting up, but the first time it did this it boiled over which is why I replaced the t-stat. Maybe I got unlucky and I had two problems and the sensor is acting up as well.

PocketsEmpty

Try replacing your rad cap, too. It's a crucial component of the system, and cheap insurance to replace. It may not be holding pressure properly which would cause the coolant to boil early and be released into the reservoir.

Worst case...head gasket. That's what I'm facing now. Runs hot as hell even after new fan clutch, system flush, water pump, thermostat, rad cap, and even hood vents.

Roadking_

I had same problem. Replaced the water pump, t-stat, heater hoses, control valve, upper & lower hoses. Then radiator and cap. Not until I replaced the fan clutch did the problem resolve itself. Now my running temp stays just below 210. Unless I pull a trailer.

GreenManXJ

I actually replaced the rad cap last night when I also tried to remove any air. I'm planning on taking it on a trip this weekend so we'll see how it does. I expected some problems when I bought it due to the miles on it so it's not too big of a deal.

GreenManXJ

Little update here. I believe I have the actual overheating problem taken care of... or it maybe not as I'm not sure the electric fan is working... but in any case I seem to be having the exact same problem as this guy.

http://www.jeepsunlimited.com/forums...n-new-to-me-XJ

I suspect it's electrical or something but haven't tracked it down yet.