Vx ss overflow dumping coolant?

[hayden2424]

Hey guys my vx ss has starting bubbling up in the overflow and dumping about a litre of coolant on me only when the car is turned off and I can't work out why. Anyone had this problem before? Could it be thermostat ,head gasket or water pump? The temps in the car stayed perfect it's just when I turn it off it starts overflowing. Any help would be really appreciated thanks guys!

 

[Munz]

when mine done this all it turned out to be was the radiator cap, grab a new one

 

[hayden2424]

Thought that but I've got a sealed radiator no cap?

 

[Nut Kracker]

There's one on the over flow bottle, isn't there?

 

[hayden2424]

Yeah there's a cap on the overflow bottle but nothing like a radiator cap just screws on and by the looks of it there's no spring for pressure relief at all?

 

[Nut Kracker]

They'd have to be a pressure relief cap, if the radiator's sealed . Rated at 15 psi.
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[hayden2424]

thanks mate didnt realise the overflow bottle cap was the same as the radiator cap. Im gonna get a new one and ill post up how i go!

 

[BlackoutSteve]

If it's not the cap, then it sounds like the system is loosing pressure somewhere else. If there are no visible water leaks, then possibly around the top of the engine where the water is already low.
I had this same symptom when the intake gaskets began failing on a SCV6 (very common and GM have since redesigned them). Bubbling noises from within and a hissing of steam from the intake manifold bolts.
Get your system pressure tested. Should hold 20psi for several minutes and maybe lose a pound or so in no less than 2 minutes. (That's considered acceptable, but best of course no loss of pressure.)

Watch the exhaust for water vapor during hot restarts.
Check your oil for a milky appearance.
Watch for excessive amounts of water draining from the heater box drain tube.
Smell a sweet coolant smell within the car?
Note the coolant level when cold every day and how much water tops it up.

 

[hayden2424]

Cheers dude getting onto Holden today to get a new cap and if I've still got symptoms I'll look further into. It hasn't been doing all the time. I drove it twice the other day and it do it temps stayed perfect and didn't drop any coolant at all.

 

[BlackoutSteve]

Water temps can often stay under control for 2 or more reasons.
1 is that the radiator capacity is ample and still able to provide enough cooling despite any excess temps being produced.
2 is that the temp sender may not be immersed in water for an accurate reading because the coolant is low.
3 is that a system that is not pressurized will boil and won't make more than 100C (or much more than 100C depending on how much glycol is mixed in). I think 100C on the gauge is only a frag above the 1/2 marker and will be assumed as OK.
Good luck. Hopefully just a cap or a hose.