Expansion tank

[Despena77]

The coolant keeps evaporating from my expansion tank on my 2006 Astra, it’s fine if I just drive around locally but as soon as I go on a longish journey about an hour or so, the thermostat light comes on and when I stop and check there’s no water in the tank,  however there is no steam coming from the engine it’s not blowing out white smoke from the exhaust, there’s no whitish gunk on the oil cap, it’s not losing performance, which I know can be signs of a blown head gasket, and when we have done pressure tests there are no signs of leaks. About a month ago I had the the WTR inlet and outlet hoses changed as they had started to perish, and this problem started about 5 days after (it was fine before), even my mechanic is at the point where his scratching his head, he doesn’t won’t to take the engine apart to change the gasket and skim, as it cost a lot of money and if it’s not that, I would pay all that money and still have the problem, and as he said it’s not showing any other signs of a blown gasket, just the coolant/antifreeze evaporating from the tank, has anyone had this problem with their Astra and if so what was it, help, thanks for any info into this problem 

[AndyR]

Hi Despena77. 

It does sound like a mind bender. Are there any signs of water leaks around the thermostat? And have you checked your carpets. Wondering if the heater matrix might have a leak which appears once engine is up to temperature. How is the heater?  hot/cold or so so? 

Another point, with it losing water once hot, could there be an air lock in the system that is appearing when thermostat opens. I had that problem on a previous vehicle, it wasn't a vauxhall, but might be worth a look.

Hope you get it all sorted, and can avoid having the engine torn down to investigate.

Regards Andy.  

[Vauxhall Owners Club]

Also worth checking the coolant expansion cap (radiator cap) is up to par if not then replace (should be about £10) but be aware if you fix this and it increases the pressure (which it should do) then it could blow other weak cooling system components