kv6 exspansion bottle
 

as title one thats tested and known to be good and cleam asap pleaseee

Tbh, I'd just go for a new cap first, it's the cap much more than the bottle that causes the problem.

yes there is a valve in the cap which fails. They are only a few quid from your local car parts shop.

ive ordered a new one so hopefully it sorts it as dont know if its worth doing the headgasket

If it's not the head gasket I'd leave it well alone, have you had a look under the acoustic cover to check for thermostat leaks.

yer cant see no leaks but the pipe work for the breathers was all broken and bodged up so ive replaced that and it still does it so hopefully cap will solve it maybe i over tightened it

I have a spare for just this reason!