Coolant Expansion tank cap - should there be a seal?
 

Hey Guys,
Just wondering if this cap should have a seal?
Mine doesn't and I think I have air in the coolant system even after bleeding/burping. I've been told the air does come back even after bleeding, so wondering if the lack of a seal keeps leaving it back in!

This is the cap I refer to (except this guy painted his red!)
http://i3.tinypic.com/wcilbp.jpg

No is the simple answer. Just clips on and isnt presurized

No it doesnt need a seal.

If you look on the side of the tank (between the cap and bumper) Theres a little hole at the top. This allows the expansion of the coolant when hot and cold.

Cool, thanks for the quick answer guys, that answers that :)

thats just the overflow/expansion bottle. As long as the pipe is submersed then its cool.
Your header tank it the important one. metal tank with a rad cap on it,left hand side of the bay.