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1999 XJ overheated today! 4.0 185,000

jackate

NAXJA Forum User
Location
New jersey
The last time this happened was like 4 years ago, and I changed out my original radiator and I was fine.

This time I was just sitting parked and all of a sudden the temp gauge went almost into the red. I started driving and got on the highway and it overheated while I was driving 65 mph.

Here is the condition of the jeep :
I flushed and changed the thermostat with a stant 4 months ago.
The fan clutch seems ok. the auxiliary fan is working.
The water pump is around 3 years old and not leaking.
The Radiator was replaced around 4 + years ago.
oil change done recently.

Here is what happened. I have not been having any problems with the temperature at all, it has been staying right in the middle where it is supposed to be until today.

When it overheated I could not get any heat to come out the vents, I thought by turning the heat on full blast I could cool it down a bit.
But not one bit of hot air would come out, I am wondering if my heater core is clogged. Why with the engine so hot was I not able to get any hot air in the car. That seems weird to me.

I had it towed to my house and started it up, and it is running fine. But the temp started climbing so a turned it off.

I guess I pull out the thermostat just for giggles. any help would be appreciated.
 
Sounds like your water pump isn't pumping water to your Heater core, or your coolant level is so low, it can't.

Take off your radiator cap and check your coolant level ... if it is full or almost full, I would bet its a bad water pump.
 
I am going to take off the thermostat and drive it for a week or so, it's August and hot so I don't care. If it still overheats it must be my radiator or water pump I guess. I'll put the thermostat in boiling water and see if it opens after I remove it to check it out.
 
X2 on water pump. Heat wouldn't be felt through the cabin vents if the 210F coolant isn't being pumped through the heater core.
 
Ok I think to be safe I will change the water pump. I removed the thermostat and put it in boiling water, and it did not seem to want to open, but I was able to push it open with my hand, but it seemed a little gummed up. still not sure if it was bad or good.

I put the housing back on without a thermostat because no part stores had the one I wanted with the bleeder hole in it.

When I over heated the overflow had boiling radiator fluid in it, when it cooled down it took some of it back, but it also took a good amount of antifreeze and water from me to fill the radiator to the top. I cleaned the hose going from the neck to the overflow anyway.

I'll see what happens in a hour when the sealant is dry and I can drive it.

But I am going to change the water pump because it is about 3 + years old and it was not an oem replacement.

Thank you I will report if I am still overheating and what the final solution is hopefully.
 
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I took it out and it started to overheat again even with no thermostat.
I got a replacement water pump I will install tonight.
It was running a little warm on the way to the parts store, but did not overheat.
On the way back it just shot up really fast the needle actually jumped. I hope it is the water pump. I will find out tomorrow.
 
The hole in the thermostat won't hurt anything but you don't really need it in '91+ xjs. Stant Superstat is good.

Somebody correct me if I'm wrong but doesn't running without some sort of thermostat potentially allow too much coolant flow which can be as bad as too little flow?
 
I think I have a blown head gasket. I read somewhere when your radiator fluid in boiling in your overflow that is a head gasket. I ran it with out the radiator cap on and it started to boil over in the radiator.

???????
 
Boiling over into your reservoir only indicates an overheating problem.

Overheating might be caused by a blown headgasket, but could also be a million other things. The fact that your heater is not getting hot, combined with your overheating problem, points very strongly to a water pump that isn't working.

It's not the radiator where it is boiling ... it's in the hot engine block. The boiling in the engine block increases the pressure (think of a pressure cooker). Your radiator cap is designed to relieve this high pressure by allowing fluid to boil over into your reservoir. Less volume of fluid in your engine-radiator system brings the pressure back down, and the pressure valve in the radiator cap closes up again. Once the engine coolant cools down again, it actually creates a vacuum in your system, and the radiator cap is designed to allow your system to suck fluid back into your radiator from the reservoir. Make sense?

Also ... don't run your motor for too long with no thermostat. Running your engine at temps that are too cold isn't good for it.

Best of luck.
 
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The purpose of your radiator cap is to build pressure. A fluid under pressure boils at a higher temperature than fluid not under pressure.

If your coolant was already at a temperature sufficient to boil at rest, leaving the cap off will certainly boil it at the top of your radiator.

Have you checked your heater hoses? Does one of them get hot and one of them is cold? That would be the heater valve not opening. Not really a cause of overheating, but it will let you know that coolant is being pumped to your heater core.

Does your upper radiator hose get hot? Again, if the coolant isn't circulating (like your thermostat is stuck closed) the upper hose will be cool because there's no coolant circulating through the thermostat housing back to the radiator.

You need to stop reading random articles on the net and replacing random parts and apply some basic troubleshooting steps to your logic. If I had an overheating problem that was catastrophic in a very short period of time, I would be concerned that my thermostat was stuck closed. You mention that you removed it and continued to have issues, but was it the same issue? Did it jump into the red quickly like before or was it a gradual rise?

Does it do it only at rest or does it do it on the highway too? If your fan clutch was shot, your fan might not be pulling air through the radiator when the jeep is sitting still. If it overheats while you're on the highway or at high rpm, your lower hose is probably being sucked shut. You need to find a lower hose that has a spring installed inside it to prevent it from being sucked shut when the pump is trying to move coolant at higher engine rpms.

There is a ton of information on this website about overheating. But you have to start at the beginning and check everything before you assume the worst.
 
The purpose of your radiator cap is to build pressure. A fluid under pressure boils at a higher temperature than fluid not under pressure.
Yes ... but the system is designed to max out around 15 or 16 PSI. Anything higher than 20 PSI or so will spring leaks in the radiator and heater core. So ... the cap has a built-in pressure relief, which allows the coolant to escape into the reservoir. When the system overheats, pressure builds too high, and needs to be relieved.

A faulty heater valve wouldn't cause the system to overheat. It would be an amazing coincidence if the heater valve failed at the same time another problem came along to cause the overheating.

He also said it overheated on the highway, which probably eliminates the clutch.

It just seems to me like all the evidence points to the water pump. But you never know, and I always enjoy reading other opinions.

Jakate: Please post back here with what the solution was ... It will help future searchers. Thanks.
 
A faulty heater valve wouldn't cause the system to overheat. It would be an amazing coincidence if the heater valve failed at the same time another problem came along to cause the overheating.

RedHeep said:
Have you checked your heater hoses? Does one of them get hot and one of them is cold? That would be the heater valve not opening. Not really a cause of overheating, but it will let you know that coolant is being pumped to your heater core.

I know, that's what I said.

RedHeep said:
If your coolant was already at a temperature sufficient to boil at rest, leaving the cap off will certainly boil it at the top of your radiator.

My point was leaving the cap off and watching the temperature rise until the coolant boils would be the reason the cap is designed to build pressure, since it raises the boiling point of the coolant. He can't troubleshoot anything by watching the bubbles when he leaves the cap off.

montanaman said:
He also said it overheated on the highway, which probably eliminates the clutch.

The only way to eliminate the clutch is to check it when it's hot versus when it's cold. Making an assumption that something works while troubleshooting will get you in trouble every time.

montanaman said:
It just seems to me like all the evidence points to the water pump. But you never know, and I always enjoy reading other opinions.

Which is why I asked for information about all of his hoses, both to the heater core and the radiator. You'll know if the water pump is working if those hoses get hot and coolant is running through them.

Even the water pumps I've had weeping still worked well enough to cool the Jeep in the summer. But your right, there's just too much sporadic information about his situation to diagnose the problem.
 
Those are all good points. And I meant no offense in my response. I just like working on jeep problems!

About the only thing I would add is that sometimes a water pump fails by leaking (but still moves the water), other times it fails by a complete breakdown, where no coolant is moving. And the radiator hoses would get hot even if the water pump wasn't pumping ... just because they have such a close and direct connection to the boiling coolant in the engine block. A frozen water pump will still cause boiling fluid to come out of the radiator cap ... and it would have to get there through the radiator hoses.

Anyway ... I hope this doesn't come off as argumentative ... I just like talking about this stuff ... it's almost like talking about sports.

We'll have to wait and see what results he gets from the replaced water pump.
 
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Here is what I have done since. I pulled off the belt and pulled on the pulley wheel of the water pump, I tried to move it side to side, and forward and back. It had no play in it. It also is not making any bearing noise when I turn it nor have a heard any bearing noise in the past. I also don't see any water leaking from it. I am going to warm it up and put something under it and check it in the morning to see if any water leaked out of it. I bought a new water pump but I don't want to waste 40.00 dollars on something I don't need to change.

I had my heater core get clogged a few years back but I think someone said that would not cause over heating. I am going to blow air and water through the heater core hoses anyway tomorrow.

HERE IS A HISTORY OF OVERHEATING I HAVE HAD IN THE PAST:

4 years ago I was having some intermittent over heating where the needle would go to very hot and then come back. I never fixed the problem in time and had a very bad over heat on the way to a family party, I pushed the engine way to far and figured I killed it and would buy a new car. It was bad! A mechanic I know sent the head to a shop to be checked out and it came back good but not great. He put on a new head gasket, radiator and water pump, and I have been fine for 4 years and the motor never sounded better.

But since then my Radiator fluid has never stayed green, it always turns brown quickly and I have noticed a tint of petroleum sometimes. I even get some caked on brown stuff around the neck of the radiator and cap. I clean it off at times. The radiator cap is brand new and 16lbs. So I am guessing the water is turning brown because of the head gasket.

I have gotten 12+ great years out of this jeep and it runs so good and really has not cost much in repairs at all.. but I think I gonna buy something new.
I just want to get it running so I am not rushed while shopping for a new vehicle.
I also noticed a little steam or smoke coming from the head gasket in the middle and the engine is running a little ruff now which is out of the ordinary.

I have to decide either to change the water pump I see nothing wrong with and does not show the symptoms of past water pumps I changed that were leaking or making a bad rattle noise or both.

Or I can spend a 100 dollars on some steel seal that is supposed to fix blown head gaskets.

Or I can change the radiator, change the water pump and add the steel seal.

or I can take it to a large automotive repair place and see if they do free diagnosis and then fix it myself, as long as it is not the head gasket.

anyway thanks for the help this board has always worked out for me and has saved me thousands of dollars.
 
If the head gasket is not holding then the system isn't maintaining pressure which would caused the engine to quickly overheat.
From your explanation above about find a touch of oil or crud buildup on the cap I would say you should have the cooling system pressure checked. A shop can also use a exhaust gas sniffer to detect exhaust gases in the coolant which would indicate a blown head gasket or worse a cracked block.
Have you had any indications of immulsified oil (water in the oil)which looks much like baby poo.... ??
 
I am thinking the problem is the radiador now.

TO CharlesS:
No the oil has always stayed very clean, and stays clean even after like six months after an oil change.

I think I am going to flush the radiator system because the fluid looks like thin chocolate milk.

I hope that will buy me some time to find a new vehicle. I will miss the jeep it has always been a great vehicle. I just put on new rear leaf springs, rear brakes, and new front pads and rotors. Oh well.
 
Today I flushed out the heater core and got all the brown water and muck out of it, I also flushed the radiator and put in water and super flush. It is not over heating but is running hot about 220-235, Most likely because I did not put any antifreeze which would of raised the boiling point. I am getting plenty of hot air in the jeep now, so maybe I was right and it is not the water pump. It did not overheat but I could here boiling water in the radiator and it pushed some water into the reservoir when I parked it in my drive way after driving for 1/2 hour.

I guess I will let the superflush and water work for a few days, and then I will flush it again add another bottle of superflush with antifreeze.
 
I did not spin the fan while it was hot. But it does not spin freely so I thing the clutch is ok. It over heated when I was driving at highway speeds so I don't think it is that.

So far I have narrowed it down to the radiator, or the old lower hose with no spring, plus maybe a bad head gasket that is causing my fluids to gum up?

I know for sure it ran better after I flushed all the brown water out. But already it is starting to turn brown again. Maybe after a day or so running with just water and superflush, I'll add new antifreeze and bottle of super flush and it will be fine.
 
Does it cool back down when you stop?

The only place I found a lower hose with a spring was NAPA. Surprisingly, it's the cheapest hose they have. It's all I run now. I spent way too much money on a radiator, water pump, thermostat and everything else only to find out my overheating problem on the highway was a "non-collapsible" hose I got from the parts store.
 
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