Coolant boiling over...NOT overheating...

[vr2jetta]

So I have removed the bottle and replaced it with an inline filler from summit. I am running a 20lb cap and as I drive it is still building pressure over 20psi and blowing off into the overflow tank. It doesn't get hot until enough coolant spills out to cause it to. I have no idea. I'm getting very irritated and about to say ef it and put the bottle back in. Any ideas?

Here is the setup. Its in a caddy.

[weejunGL]

20PSi is just about right, if you have an expansion tank, if not, it will blow it off, it expands due to the pressure caused by heat and steam, so you need some kind of expansion tank, and i can't see anything there? i can see a vent hose from the filler neck youve mounted, but that won't allow it to expand enough


remember that its a reason its called an expansion tank

[vr2jetta]

So, doing away with the expansion tank is not possible?

I really hate to look at that big ugly bottle under the hood....

[weejunGL]

you need somekind of expansion tank

[vr2jetta]

Well, today I removed the inline filler and installed the factory expansion tank and its still doing the same thing. The factory coolant cap is opening and the engine isnt even hot. Im gonna have to pull it apart and flush it to see if there is blockage. I did however see water flowing through the small line in the expansion tank while filling it. Im about over it...

[vr2jetta]

Pulled the cap and saw bubbles rising up constantly with no coolant going down or overflowing. revved the engine and shot a 3 foot geyser out of the filler neck. Changed the head gasket and problem solved.