It finally happened to me (Another hot XJ thread)

Well I was out on the trail this weekend for the first time in a while. My jeep started running hot and actually boiled over the overflow bottle. I have replaced my plastic tank with an aluminum one (Eagle style) over a year ago. I also just did a new radiator a few weeks ago and a water pump a few months ago. When I found I had a problem I turned around and headed for home. As long as I kept moving it stayed at like 130 but if I stopped or had to slow way down on the trail it would start to climb to like 150. I’m thinking the two possibilities are:

• It has a bad fan clutch. Do they tend to go bad all at once? It seams like this would be most consistent with the speed related temp. Yes/No?
• The thermostat failed closed. Can anyone rule this out from what I have said?
• Something in the system is clogged up, possibly related to the new radiator or this being the first time I have wheeled it in several months

Was that three? Ya three. All the parts stores where closed by the time I got home so I have till Monday to figure it out. At this point I’m thinking just replace the Fan clutch and the t-stat and see if that would do it. Any help is appreciated.atriot:

You must mean 230 - 250?

Seems to me maybe you've got a pressure leak. Coolant is held under pressure for the very reason that it will boil under normal a standard atmoshpere of about 29.92 inches merc. Boil's law is the principle under which your coolant won't boil until it reaches a higher temp IF it's kept under pressure. You still running closed? Check for a pressure leak.

If it's not pressure then your looking at a clog of some kind or a failed pump. There's simply not much else that the cooling system needs to operate other than pressure and movement to allow cooling. Good luck.

you probibally should put a switch on your electric fan, so you can controll that, so at slow speed you can have that thing going all the time, also you may wanna make sure there are no small leaks, i know mine had small leaks in the past, and would heat up like that when it was getting low on fluid.

After cooling system repairs, even after burping most of the air out of the system. I´d occasionally overheat a few days later. Was often, the air I missed the first time, collecting in the radiator top hose, squeezing the hose with two hands at the highest point (motor running at operating temp.), in pulses, until it makes a sound like a demented suction pump, has lowered the coolant level in my surge tank pretty quick. Tells me there was still air in there someplace.
The new thermostat OEM, with the bleeder hole in the stopper, really helps the air to move through the system. Or S-90´s method of drilling a small hole through the themrostat stopper (top), could also be helpfull.
Like mentioned before, pinhole leaks (hardly noticeable) that don´t leak enough to drip, have given me fits in the past. Often the only way to spot them, is by the stain, from the coolant (red/green) and/or lime (white) stains and a real close look with a flashlight.

One thing you might check is whether the radiator is uniformly hot when the engine overheats. If it is, then your problem is probably mechanical - fan not working, pump not pumping fast enough, etc. If it is cool, then you should look for low coolant, air locks, pump failure, or thermostat problems that would prevent full circulation.

Just disconnect the temp. guage!! :twak:
Okay...air in system is my guess...
After flushing it seems to be the biggest problem...
but....check your T-stat in a pot of boiling water...if it opens (maybe you have a cooking thermometer and can check when it opens) than you can rule it out as a possible cause...
Good luck

rick