E30 Zone

Hello,

My coolant expansion tank cap seems to be weeping a little, should the cap screw down onto a rubber washer?
If so then I must have lost mine at some point.

Many thanks

It should indeed have a rubber washer in the cap.

Well I wonder where that has gone!

Thanks

The rubbers can easily slip out after they get worn.

This is what you need to be seeing.

Flat rubber washer at the top has nothing to do with keeping coolant in. The O rings on the side are the pressure seals.
The cap in the pic. is from an iS, which uses a different (2 bar) cap from the 1.4 bar cap fitted to most other E30s. Unless your car is an iS, the original cap should have been replaced under a safety recall around seventeen years ago, which is still active. Most replacement caps have a yellow disc at the bottom instead of black, so if yours doesn't appear to have been changed, visit your dealer for a free replacement.

That's some good info. Wish I've known about it before replacing my black ring one with a new yellow ring one.