So I've been having an odd coolant leak. Vehicle drives fine, but when I come to a stop and turn it OFF, it begins to spray or bubble coolant out from under the radiator cap. I have already replaced the cap (yesterday) with a new locking one, the radiator has been flushed, and new water pump, no-fail tstat, and tstat housing. What is causing this?

Edit : Also brand new head gasket. Good compression in all cylinders, NO coolant in the oil.

 

Could be a bad head gasket.

 

Brand new head gasket. Did a compression check, good compression in all cylinders.

 

Still could be a bad HG. Was it done by you?

 

Yes it was, but would I not have coolant in the oil, or compression issues with a bad HG?

 

Open or closed cooling system? I had this problem when I first got mine it was just a bad cap

 

sounds like there is some air in the system. start it up with out the cap on turn on the heat and let it run for a little. wait for the tstat to open and keep an eye on the coolant level.

 

I did the above, the coolant level did not change, and I was looking at my coolant tank.. I think I found my problem! I pulled the hose that goes from the radiator cap to the coolant tank, and tried to blow it out with my compressor. Got fluid blown all over me where the air was going in - so it's clogged. Took a can of Throttle Body Cleaner (since I had no BraKleen on hand) and sprayed into the hose real good, then I put the rubber fitting from my compressor back into the hose, sealed it with some duct-tape, and BAM, a small pile of CRUD came flying out of the hose, sprayed it out until water ran through clear and re-attached. Will see how it goes when I drive to work today.

 

Not always. You can bridge a coolant or oil passage with the combustion chamber and not mix fluids. And compression doesn't always go low with a bad HG.
Should be open in a 96.
I'd think the temp gauge would be all over if itwere really a bubble.
That could very well be the cause. Keep an eye on it just to be safe.

 

nah youd be surprised. air could be stuck somewhere away from the sensor.

but the cloggyness could be the problem.

 

Ran it all day, not a single leak. Was the stupid hose after all.