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need a quick answer to a overheating question


NAXJA Forum User
so i have had great temperature with my engine all of its life. Never any problems with over heating and such. but then earlier tonight i parked at my friends house, left the car on and went inside, 15 minutes later the coolant resovior... cant spell it... smoking and the engine temp is around 230, i freaked out an just turned it off. this is an 89 cherokee so the coolant holder is in the left corner of the engine compartment, there is nothing leaking in the system and the resvoir is still full from where i last filled it. What caused my overheat problem?
also when i left my buddies house shortly aftert that and drove it had no overheating problems and stayed right around 210, which still is a little higher than usual but isnt a issue. I am goin on a big wheeling poker run ina week so i want to make sure this isnt a issue on the trail.
is this a thermostat problem or did it just get jammed and not let the system flow like usual?
thanks for the help
This is a very common problem.What is probably happening is your "resevoir" is accually a pressure tank for the cooloing system, alot of times it is either the cap on the tank is bad and will no longer keep the right amount of pressure in the system or the tank is cracked and allowing pressure to escape. Also check to see if the electric fan is coming on . Mine doesn't come on until it is running about 215 degrees. All these will cause an over heating problem when your XJ is sitting still and running. You won't have the over heating problems when driving because there is alot of air getting moved through the radiator when driving to keep things cool. Good Luck.
You didn't say if you still have the original radiator, but if so it's probably long overdue to be replaced. The radiator on my 88 sprung a leak back around 2000, IIRC, and when I replaced it I could see that the cores were mostly plugged up with corrosion anyway.

Also, your viscious fan clutch may be tired. When this happens the primary mechanical fan doesn't spin as fast as it used to, causing over heating especially at idle and low speed.
the radiator has been changed so i dont think that is the problem, and i have never had a problem with my fan

but the original coolant resovoir failed on me last year so i replaced it with just a factory one for 80 dollars.
Is there some sort of better resovoir i can buy..... one not necessarily for a xj? Becasue i have a feeling it has to do with the cap failing becasue there is a lot of corrosion of antifreeze around the cap.
is there like a metal one or something somebody sells that would hold up better?
You described your XJ got warm when it sat there at an idle. That means not enough heat was leaving the radiator. It takes moving air to get heat out of the radiator.

If the AC was off the electric fan should of kicked on once you were over 210F. It hard to know what temp the fan turns on since it a switch in the radiator, not an engine based sensor.

If the radiator is new then you need to look at the fans. There is NO reliable test for the fan clutch. Just go out and buy a new one and install it. I have heard anything over 5 years on a fan clutch is just luck. Take the old clutch with you. On my 88 XJ I have purchased fan clutches from CarQuest and O'Reilly which were the same size and shape as the OEM AC/Delco unit.

Go buy a new fan clutch and install it. That should solve the problem. Since you were boiling over out of the pressure tank I'd suggest you replace the "radiator cap" and the thermostat. I found the dealer is the only place I can buy only a "radiator cap" for that pressure tank. I can get the tank assy with cap from quadratec. While at the dealer get a new thermostat, you moste likely damaged it also.

My raditor shop in st louis told me after my over heat that one time at 225F can damage a thermostat. Since the cap and thermostat use the same technology replace both, it a best pratices thing.

You operated your XJ in a manner it was not use to, now you have revealed a few weak parts, fix them now. It part of owning an older vehicle.
NAPA has the exact same "radiator cap" for A LOT LESS than you'll pay at the steelership. What actually fails on the cap (in my experience . . . two '88's) is the gasket. I've been making replacement gaskets (from innertube material/rubber) for years and I keep a spare or two in the jockey box. Don
dellstopjeep said:
Is there some sort of better resovoir i can buy..... one not necessarily for a xj?
Yes. Moroso speed equipment makes an aluminum surge tank that's perfect for this job. The swap has been written up, probably in the Mod Tech forum, and someone (MaXJohnson?) has posted pics.
It could be your thermo. I had the same problem on my 92 (different cooling system, I know) I popped open the t-stat housing to discover the spring retaining bracket had failed allowing free flow of coolant through the t-stat. Replaced it and have had no problems at all. Corrected my overheating condition immediately.
put antifreeze in it today and it cooled down, then i got home from work and it hadnt overheated, but the resovior is empty and i can hear the pressure system boiling kind of from the cap.
Does this help pin point it at all.
unfortunatly i dont have money to afford a new radiator cap, thermostat, fan clutch, and resovior or i would just do it all.
dellstopjeep said:
put antifreeze in it today and it cooled down, then i got home from work and it hadnt overheated, but the resovior is empty and i can hear the pressure system boiling kind of from the cap.
Does this help pin point it at all.
unfortunatly i dont have money to afford a new radiator cap, thermostat, fan clutch, and resovior or i would just do it all.
I thought you previously posted that the coolant level was okay.

The same thing happened to me in the 87 MJ last week. I hadn't driven it for awhile, and either the water pump is weeping or I have a loose hose clamp. Drove it without checking the coolant level and suddenly noticed the temp needle nudging into the red.

I pulled into a nearby parking lot and waited for things to cool down, then opened the bottle. Empty. Got some water from a nearby garage and filled it up. Went through the "burp" procedure a couple of cycles to get the air out, then continued on my way. On the way home I bought a gallon of anti-freeze and I've been topping off with that to restore the mix to 50/50 status.

The temp sender is at the top of the head, which is almost the highest point in the system. It doesn't take a lot of air in the system before water (coolant) doesn't go there. This leaves the sender in a section of head that isn't being cooled, so what it reports to you is the temperature of the steam that's going by it. When you add coolant to the bottle after an incident like this, you have to get the entrapped air out. Usually this takes a few cycles of heating up, purging the air, and drawing coolant back into the block. If you don't refill the bottle during between these cycles, it'll draw in air and you get to start all over again.
i just went and did some more looking and noticed that the aux fan isnt turing on when the temperature heats up. it works when i turn on the a/c tho. i looked at the diagnostics and there is a switch that turns on the fan from the radiator at 190 degrees. the little switch that does that may have failed and that fan isnt turning on. it is a cheap fix so i am going to try that. may also replace the thermostat becasue it may be shot with me overheating it yesterday. both inexpensvie. no hoses are leaking and the resovoir cap is fine im almost sure of it. so i think i have pinpointed it to these two things. if anyone thinks im steering in the wrong direction let me know before i waste my money.
eagle, i will take that into account when i refill the coolant.
thanks for the help
hey guys im having similar problems with an 87 im working on right now. The coolant bottle doesn't look factory at all, it just has a tube running from the top and looks like the one in my 96. The water temp guage shoots all around and is usually really hot and the fan always runs.

compression check was like 110, 110, 90, 85, 105, 110

sound like a head gasket leak?

there were 2 small balls of.. looked like grease, in the coolant bottle today that i pulled out. Is the radiator backing up? jeep has a vacuum issue too, there isn't enough vacuum for the brakes to work right.

thanks =)
it idles at like 500 rpm's.. if you hold the brake in it goes up to almost 1k rpms, then when you let off the brake it almost stalls...

i guess im taking it down to this garage so the old man there can look at it cause im pretty sick of it anyway