Quote:
Originally Posted by SalvadorP
What you see probably isn't several leaks over a period of time, it's just me having opened it several times in the last few days. I was under the impression that the level shouldn't rise when you open the cap even if the car was hot. I'm starting to learn hiow dumb that is...
What about the steam/smokle coming out? Is that normal?
I was considering doing a flush anyways. But I?m also considering doing a head gasket test. Do you think I'm being too cautious/paranoid? The car doesn't have other symptoms. No smoke. Also the echaust doesn't have any smoke build up. No overheating at all. And today I drove it up the mountain for quite some time...
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I saw the recent opening evidence, i also saw the much older, crystalline deposits on the seam where the top and bottom halves of the expansion tank meet.
The level will rise because the system is pressurised which compresses the air in the system - this expands when the lid is removed dropping the pressure in the system.
Given the coolant is going to be in the region of 88-92C, steam is perfectly normal, yes. Also if you took it up in the mountains where the air is at a lower ambient pressure, there is more of a chance of it boiling due to the pressure difference. If it behaved during that then the chances are the HG is ok and so is everything else except maybe the expansion tank cap.
Given the evidence, i would try a new expansion cap first and once fitted, leave it alone unless the engine is cold. Top up to the "MIN" mark when cold, it should go up to about the "MAX" mark when hot and whatever you do,
DO NOT OPEN WHEN HOT!!!!! 
If my suspicions are correct and the existing cap has gone weak, when you fit the new one and it pressurises correctly to 1.1bar/kPa or 1.5bar/kPa depending what the existing one is rated at, this is either 16psi or 22psi - that's a lot of force behind scalding hot coolant!
Opening the cap with that force behind the coolant would see you getting a hot shower - scaldingly hot!