V6 Coolant Not Returning to Radiator

[wortus]

I've got a problem with my VY V6. The coolant is expanding into the expansion tank on the passengers side but not returning to the radiator when the motor cools down. There is no overall loss of coolant the excpansion bottle just keeps on filling up if you top up the radiator.
There's no leaks to be seen anywhere, no trapped air in the mainfold, the radiator cap is new and the hose from the radiator to the expansion tank is OK.
Anyone had this problem and managed to find the cause?

[Sean880]

Looks like no comments from other owners.

I have not had this problem in a vehicle but presumably you have one of the following conditions:

1. The spring operated vacuum valve at the base of the radiator cap is not functioning; or

2. There is a very tiny air leak in the plumbing linking the radiator with the plastic reservoir tank killing the vacuum required for the siphon effect; or

3. There is a tiny radiator air leak allowing air to be drawn into the radiator itself when the fluid is cooling and contracting thus negating the vacuum needed to siphon coolant back to the radiator.

Cannot think of anything else given your description of the symptoms. Interesting problem but frustrating. Good luck with it. I am sure some radiator guy would have seen all this before and can tell what they found on other cars.

[RiCeY]

As said replace the radiator cap.

[illlusion]

its also the sign of a head gasket leak just done one on a vx this week goto a mechanic and ask them to do a tk test to see if any exhaust gasses are entering the cooling system and ask them to pressure test the system aswell

[wortus]

Thanks for the replies. I've replaced the cap and it didn't fix the problem, spoke to a friend and his VT was doing the same thing from almost new, Holden couldn't fix it. I'll get it checked for any blown head gaskets or inlet manifold gaskets however I'd have thought this would lead to the coolant being lost where as it's just going into the overflow and not coming back.

[RiCeY]

Check that the hose going from the radiator to the overflow tanks isnt kinked or have any holes/splits that would prevent water being drawn back into the radiator. Also make sure the hose is seated in the overflow bottle properly.

[wortus]

So I've just checked under the hood and if I take the overflow tube out of the bottle, still attached to the radiator and suck on it there is no vacuum unless I push down on the radiator cap then it seals and pulls a vacuum. I'm assuming the cap is not tight enough on the radiator either the tabs on the cap need to be bent in a bit or the top of the radiator is worn thin? It's only a new cap and I am sure it is the correct cap.
I'll bend the tabs in a bit when it's cooled down, refill it and see how it goes.

[wortus]

Bent the tabs on the radiator cap as it was not sealing to the top lip of the radiator filler. It holds vacuum in the overflow hose now and the coolant is returning to the radiator.