Overheating issue and need help

I had a new thermostat put in my 2000 XJ about one month ago. The jeep drove flawlessly for that time period until about two weeks ago. One morning I go out to start the Jeep and she was overheating within 15 minutes of starting it. I live in Montana, so it’s been about -10 most mornings. Anyway, I now think the thermostat is stuck in the closed position. The upper radiator hose is cool to touch, so I know there isn’t any coolant being run through it. Unless if anyone else has some ideas, I guess I need to buy a new thermostat and try again. This time I will be installing the thermostat myself.

Did the shop that installed your t-stat flush the cooling system? Why was the t-stat replaced in the first place?

MT Mike said:

Did the shop that installed your t-stat flush the cooling system? Why was the t-stat replaced in the first place?

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I just bought my first XJ, so I took it to a guy that does Jeep work on the side. He went through the entire Jeep and basically changed all the things that needs routine maintenance. But to answer you question, he did flush it. I used the Amsoil Coolant.

dieselenthusiast said:

I just bought my first XJ, so I took it to a guy that does Jeep work on the side. He went through the entire Jeep and basically changed all the things that needs routine maintenance. But to answer you question, he did flush it. I used the Amsoil Coolant.

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Might be a defective t-stat then. :dunno: When you replace it, be sure to buy a Stant Super-stat at the factory 195 temp, and install it with the spring in. Don't get anything cheap, as they don't tend to last.

So where in MT are you?

MT Mike said:

Might be a defective t-stat then. :dunno: When you replace it, be sure to buy a Stant Super-stat at the factory 195 temp, and install it with the spring in. Don't get anything cheap, as they don't tend to last.

So where in MT are you?

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Yep, I’m about to order online the Stant SuperStat boxed 195 thermostat.

I live near Billings.

Do thermostats come with a gasket, or do I need to order a gasket separately? Also, do I have to drain the coolant, or can I change the thermostat without draining the coolant?

dieselenthusiast said:

Yep, I’m about to order online the Stant SuperStat boxed 195 thermostat.

I live near Billings.

Do thermostats come with a gasket, or do I need to order a gasket separately? Also, do I have to drain the coolant, or can I change the thermostat without draining the coolant?

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Buy a new gasket (less than .50 cents). You might be able to salvage the one you have now, but if not you'll have one on hand ready to go. As far as draining your coolant, just get a catch pan underneath the front of your engine and disconnect the upper rad hose at the stat housing. You'll lose some coolant out of the hose (the majority of which will end up in the catch pan). Use a heavy duty spring clip (like this) to clamp the hose shut and change out your t-stat. Put everything back together, pour in your recovered coolant, top off as necessary, and you're good to go.

Just hope that you don't have a cracked block, popped out freeze plugs, or a blown head gasket from the coolant freezing in the block, that can also cause the symptoms you're seeing especially if the engine overheats. The thermostat is at the front top of the engine, so you don't need to drain the coolant, heck you can probably get away with putting only a quart or two more in afterwards if you park it nose up on a steep incline before pulling the thermostat housing.

kastein said:

Just hope that you don't have a cracked block, popped out freeze plugs, or a blown head gasket from the coolant freezing in the block, that can also cause the symptoms you're seeing especially if the engine overheats.

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How would I know if I had a cracked block, popped out freeze plugs, or a blown head gasket? And would coolant freeze in the block because the mixture (freeze-point) was too weak? We did hit -28 once this year.

cracked block - you'll have some combination of bad mechanical problems. Losing oil, losing coolant, oil in coolant, coolant in oil, crappy mileage, crappy compression/leakdown, SOMETHING will show up.

blown head gasket - you'll get water in oil, oil in water, crappy compression/leakdown, crappy mileage, or coolant coming out the tailpipe are usual signs. This is most likely if it overheated and you felt the coolant hose and it was cold or barely warm.

popped out freeze plugs - losing coolant, it'll be coming out and trickling down the engine once you get it warmed up.

If you had too little antifreeze in the coolant, you definitely could have frozen the block, hopefully not though.

EDIT: obviously hope for either the gasket or the freeze plugs, preferably freeze plugs. They're pretty cheap and aside from getting to the darn things (might have to pull manifolds for some, or get annoyed working on the back of the head right by the firewall) not that bad to replace. If this is your problem, substitute a block heater for one of them while you're at it.

EDIT2: also, these are worst-case scenarios, try the thermostat first. If it's just that, I'm scaring you unnecessarily.

kastein said:

EDIT: obviously hope for either the gasket or the freeze plugs, preferably freeze plugs. They're pretty cheap and aside from getting to the darn things (might have to pull manifolds for some, or get annoyed working on the back of the head right by the firewall) not that bad to replace. If this is your problem, substitute a block heater for one of them while you're at it.

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Thanks for all the help. I wish I lived closer to some local shops or belong to a local Jeep Club. So far, the engine seems to idle fine, but I haven't driven it due to the overheating issue. The first morning that it overheated I shut her off as soon as the check engine light came on. I then let the engine cool and drove it back home. The upper radiator hose also sprung a small pinhole leak that day. So I bought a new radiator hose and installed that. There seems to be no coolant leaks and the motor oil looks good and she idles fine.

kastein said:

EDIT2: also, these are worst-case scenarios, try the thermostat first. If it's just that, I'm scaring you unnecessarily.

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I bought the XJ as a project vehicle, so it’s not necessarily a major issue. But I’ve been using it as my daily driver to keep the miles off my newer Jeep. We only paid $2,200 for the XJ, but I promised my wife that I wouldn’t start building it until next year. So lets hope you're right, and the scare is unnecessary.

When you change out the thermostat, make sure that it stay properly located in the head recess and doesn't slip down. The burp toggle will be in the up position. It's a tiny hole with a bit of brass clinched in it loose.

When you fill it, don't assume that when the radiator is full that it stays that way. Run the engine until warm, check again. What happens is that the radiator is almost lower than the engine block, when the system is opened up an air bubble will be introduced. Purging that bubble is mandatory because it will cause the system to underfill and overheat. Keep checking the coolant level in the radiator (be careful) because it may not siphon all the coolant back into the system. Don't use a safety lever type cap as they don't allow coolant back in.

It's a more complex system than some imagine, all the little things have to be done right.

I had a bad water pump, so that was the problem all along.

dieselenthusiast said:

I had a bad water pump, so that was the problem all along.

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Please describe its condition.

joe_peters said:

Please describe its condition.

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I learned that a bad water pump has similar symptoms as having a bad thermostat. So my friend suggested that we check the water pump. Upon firing up the Jeep, he could hear it squeal a little plus the water pump had some play to it. We changed the pump and I had no more problems with overheating.

Sounds more like you had air in the system than the water pump if there was nothing wrong with the pump fins.

Air can become trapped if the t-stat doesn't have a bleed hole in it and it's not installed at the top. Air can get in the system if the overflow bottle gets too low or the connections/hose leaks also.

dieselenthusiast said:

I learned that a bad water pump has similar symptoms as having a bad thermostat. So my friend suggested that we check the water pump. Upon firing up the Jeep, he could hear it squeal a little plus the water pump had some play to it. We changed the pump and I had no more problems with overheating.

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Thanks for the the further information. Another recent poster had his WP fail and the impeller was contacting the inside of the WP body and was really digging into it.