So If you observe bubbles in the coolant what exactly are the chances that your HG's are blown?

do a search on how to burp the coolant system, could just be trapped air in the system...

 

Others will chime in shortly

*chime*

 

have you done anything to the cooling system recently?

 

Replace your radiator cap just in case.

 

nipper

investigate further, remember that diagnosing over the internet is quite a chore....so more info is good. how are the bubbles happening? any overheating? are the bubbles happening all the time or only some times...like after overheating and shutting the car off?? etc.....bubbles alone don't verify anything.

I have known blown HG's, I've listed my car's symptoms below.

 

Strange, unexplained temp "spikes"

Any "mysterious" coolant loss

Boiling over at the overflow tank.

 

If the bubbles are accommpanied by these symptoms you DEFINATELY need to look closer.

An easy test that will help you to decide if you need to have a hydrocarbon test run on the coolant; Let the engine run until the bubble appear in the coolant tank. After they start, close the tank for about 30sec. Then open it up and sniff. If it smells like exhaust, go get a HC test done.

 

I wish you luck.

well i dumped out my coolant resevoir to clean it......than i filled it again with new fluid....saw the bubbles the first time the car came to operating temperature....and since have checked it like 5 times and didnt see any bubbles at all.....

Cool Beans!

 

I'm glad it was something so simple.

Seeing bubbles immediately after doing coolant system work sounds completely normal. Do you mean you just saw them after and not before the cleaning?

 

What prompted the cleaning...perfectionism or did it look like total nastiness in there and you have other reasons to believe there are cooling system issues?

 

for any pre-2000 Subaru's the head gasket problems are almost always accompanied by overheating.