Water pressure problems

[johnny5]

So I have been having a cooling system problem that has just appeared.

The car is letting out water into the overflow tank while it is not much its still worrying, then when it cools it kinda sucks it back in it hasnt started spitting out of the overflow tank but am pretty baffled as to why. The car is not overheating but I can faintly smell coolant so maybe there is a leak?

At first I suspected the head gasket but Im not blowing white smoke, no signs of water in the oil I did however take the radiator cap off and run the car while I didnt notice bubbbling the water did expand pretty fast.

The radiator cap appears to look ok but there is a white stain round the rim where the cap goes on.

While my first thought is to buy a new radiator cap what else can I do to check my head gasket is good and solve the rest of my problems before I take the car in to do a pressure test on the system

[mondo]

Are you saying its filling up the expansion tank and spilling out, or getting to the hot mark like it should?

[johnny5]

Filling the expansion tank a bit more than it should but not spitting out the car has mever done it before

[gazzy2000]

could be an air lock.. whereby components in the engine where the air is get real hot and when cool water does actually flow past it it boils instantly.. which is especially true when u remove the cap as this can make water flow properly into/past the airlock and as it does the water instantly boils blows it out the cap. makes u think its H/gasket.

So bleed system properly first i.e. jack front of car as high as poss etc

[johnny5]

I changed the radiator bout 3000kms ago I would have thought an airlock would have shown itself along time ago, just thought it could be the H/G cause I could smell coolant b

[gazzy2000]

A leak down test wud tell all then

[johnny5]

Cheers gazzy might just go do that

[johnny5]

pressure tested the cooling system and is ok new radiator cap also seems I was worried about nothing and on a even better note passed my new WOF with flying colors