Coolant Tank- not stupid, just ignorant about some things

[tommygunn]

I'm dealing with this same issue, and this thread appears to be one of the more complete ones on the subject, so I thought I'd post here asking for an update. Any solution identified?

I too have upgraded to the newer expansion tank cap, and have tried to "burp" the system a few times. I always hear some air gurgling when I open the valve in the trunk. Mine started dumping coolant after I had the IMS done, wherein the mechanic topped off the coolant because he said it was a bit low. Probably the engine was totally cold at that point and he overfilled it.

Today the car dumped a lot of coolant at the right wheel after a 30 minute drive on a slightly cooler day. The expansion tank shows an above "full" level now. Looking at the anatomy of the expansion tank, it appears that when you exceed the "full" level the coolant just runs down an overflow hole for this purpose, which is why it always dumps in the same spot and why the trunk is never wet. I noticed that the temp gauge was pointing straight up after running the car at idle in the garage for a few minutes before I turned it off (it's usually closer to the 180 degree mark), and the fan had just come on right when I turned the car off. A couple minutes later it dumped a lot of coolant.

How can you differentiate between an old leaking valve vs. other problems?