Came home at lunch from a couple errands around town. Did not notice engine overheating light nor get any audio warning (don't know if I should have). So, I don't know if I overheated or not, there were no drive-ability issues, steaming, engine missing or anything.

Parked for about 40 minutes came out and noticed a puddle underneath. Investigated and discovered the radiator overflow tank was puking coolant out overflow vent.

The overflow tank was full. Engine was cooled off enough to open radiator cap, coolant was to top of neck. Ok whats up with that. How could this mysteriously occur all of a sudden? What displaced enough fluid out of somewhere so that both the overflow and radiator were full to the brim? Coolant had cooled off enough that I could stick my finger in it by this time by the way.

Tonight, with a flashlight, I observed the coolant in both the radiator and the overflow tank and it was green and didn't appear to have oil in it but I really need to have another look tomorrow. Oil was clear. I was afraid of a blown head gasket since it has been leaking oil for some time on the passenger side. Could a blown head gasket be allowing air to be sucked into the system and it displaced the fluid? Any other ideas.

Engine has about 204000 on it, got a bad feeling I may need a new one. Any thoughts on this issue for I hit the panic button?

 

Was there any corresponding changes, recent work done or anything like that? Just a random out-of-the-blue event?

204k is barely broken in on an I6...

 

I had the same exact issue, for me it was the fan clutch that solved the problem. (Someone else had a similar problem and I remember for him it was the radiator cap.)

 

A weak radiator cap could certainly explain the problem - especially if it was out-of-the-blue.

A bad fan clutch would cause overheating.

What I would do is verify the head gasket (compression/leak down tests) is seemingly good. I'd check the coolant system pressure as well. Test tools are typically available at your local parts retailer.

If that goes well (in other words, no obvious head gasket failure), then replace the radiator cap. I would replace the fan clutch as well since it's cheap and pretty easy to replace.

 

I got the same thang goin on. My cooling system operates perfectly but when i run it for a while and park it i get a puddle of coolant. Why does the fan clutch and rad cap cause this?

 

We're making a bold assumption - that the fan clutch and cap are the root cause. A cooling system pressure test is needed to figure out if the system is ok (holding pressure) and not leaking.

The fan clutch is the primary cooling fan that moves air across the radiator when the temp is sufficiently high. If it is weak/failing/bad it won't move air when necessary (typically idle or under load). This causes the coolant to get hotter than normal (normal being about 210F).

The radiator cap is designed to maintain pressure in the system. Pressure keeps the temp lower, it also rises as the coolant heats up. When a certain pressure is reached (16psi) the cap releases, allowing coolant to overflow.

So, ASSUMING that the clutch is bad (not moving air enough to keep the temp at normal) AND/OR the cap is bad (opening at a lower pressure than 16), the hot coolant builds pressure, shoots past the weak cap and overflows the overflow tank.

What concerns me is that it seems like an awful lot of coolant coming out to overflow the tank. If you've overfilled the system, maybe, but...

The cap is a no-brainer - if it's even a question it's worth the >10 bucks and 10s it takes to change it.
I personally would change a questionable fan clutch because it's a $40 part and is easy enough to do. Others may not be as quick to do so, but I would (and did, and it turned out the old one on mine was leaking wax so clearly it was bad).

 

One day I stopped to gas up and the '00 started puking coolant out of the overflow tank. Replaced the radiator cap and all was good.

 

Probably just the cap not holding pressure which increases when you turn the engine off.

Did you go open system?

 

This was an out of the blue occurrence. And as I think I said the vehicle had cooled off enough to remove rad cap when I noticed the fluid. So, I did open the system. But why did it not flow back into radiator as it cooled?

I am gonna start it and let it idle and see if it overheats and/or if it repeats the puking. Maybe it has the flu. It is raining and I don't want a bunch of puke in carport so t'll have to wait a day.

Stay tuned- I will report back. And thanks for ya'lls input.

 

This was an out of the blue occurrence. And as I think I said the vehicle had cooled off enough to remove rad cap by the time I noticed the fluid. So, I did open the system. But why did it not flow back into radiator as it cooled? And, why was the radiator full as well as the overflow tank after the coolant had cooled down enough to remove cap? Hmmmmmm.

I am gonna start it and let it idle and see if it overheats and/or if it repeats the puking. Maybe it has the flu. It is raining and I don't want a bunch of puke in carport so it'll have to wait a day.

Stay tuned- I will report back. And thanks for ya'lls input.

 

Cruiser was asking another poster whose XJ came with a closed cooling system if he had converted to an open system. Not if you had opened your system.

Sounds like your cap isn't sealing so it's not holding pressure.

"why was the radiator full as well as the overflow tank"
Is it possible you have too much coolant in the system? How far above the full mark on the tank are you?

 

It is at least 3/4 full. I just removed radiator cap and started engince to see if I had air bubbles. After only running a couple minutes the radiator started overflowing out where the cap goes. It wasn't running long enough to barely start warming up, maybe 2-3 minutes. Just passing this on if it is any help.

 

Coolant level in the overflow tank should be no higher than the "full" line. The radiator will overflow with the cap off and the engine running as it's building pressure. Try a new cap. It needs to both seal and work properly for the system to work as it should. Coolant returns from the tank to the radiator as the engine/coolant cools down.

 

Your cap is definitely bad. Go to the parts store and see how much easier it is to push the inner part down on yours than the new one (or how bad the seal is.). It should be good and hot before the pressure is high enough to push into the overflow. 16 lb cap - make sure it's the correct pressure and size. Just because it fits doesn't mean it's right.

 

Sorry, I misread that - I didn't realize the cap was off. As EZEARL said, there will be plenty of overflow in to the tank with the cap off.

Also it's possible that the system only "appears" full - once you have a new cap and jug of 50/50.. run the engine until it warms up with the cap off. Best if you elevate the drivers side by parking on a hill. There may be air in your system that you need to expunge. Running it with the cap off and elevated will make sure you get the air out. If it sucks the coolant down rapidly as it's running, top it off carefully until it doesn't take any more. Then carefully put the cap back on.
If your system is full and the "burping" was unnecessary, at least you'll know it's good. Then as EZEARL said - do not overfill your reservoir. There sometimes is a "full hot" and "full cold" and depending on your engine temp - it should not exceed the corresponding line.