coolant cap

[Craigwilson]

hi all I was wondering what is the actual difference between the blue cap and the black cap because when I use the blue cap all of my coolant hoses swell up when warm and then when you unscrew it you can see them deflating again.

when I run the black cap the hoses don't swell up but over time (a few weeks) my coolant level get low.

can anyone explain this?


regards,

Craig

[Sgt_Lemon]

The black cap isn't holding the pressure (hence no pipe swell) and is leaking because of this rough the cap. The blue cap is the proper one.

[Craigwilson]

is it okay that the pipes are swelling?

[Ben@VWH]

They changed the colour of the cap from black to blue when they changed from g11 to g12 coolant.

The system does need to be sealed and under pressure to raise the coolants boiling point. A bit of pressure in the hoses is normal.

[Waspy]

They changed the colour of the cap from black to blue when they changed from g11 to g12 coolant.

When did they do that?

Mines a J reg and has a black cap. Does that mean some plonker of a previous own has changed the coolant cap on mine?

[Craigwilson]

yes mines is an H and had a black cap, and that might explain why my coolant is dropping with the black? no pressure there's for it is evaporating and finding a way out? I'll try the blue and take it a run and see if It even makes my coolant gauge move off the white mark

[Sgt_Lemon]

The coolant system is pressurised when hot, if you were to pull the temp sender on the flange for example the coolant would piss out everywhere until it equalised. If you get the coolant hot and slowly release the reservoir cap you should hear a hiss.

[Waspy]

Well that's what I was thinking, the black cap on mine seems to keep the pressure, and it does hiss if you take it off. I was just confused since mine is a late model and apparently they changed the cap during production...

[Craigwilson]

my black cap doesn't hiss ? but when I remove the blue one the diameter of the hoses reduce by about 1/2 and inch

[gazareth]

my g plate has a black cap and I just throw in whatever antifreeze is handy and never had any bother with it. if I happen to overfill it it seems to lose some and find its own level and stay there.