hi guys ,
just noticed this today

I think there should be a gasket - rubber on the inner (lower) sealing shoulder of the radiator cap

can someone confirm this ?

might explain a few things about expansion into the reservoir

Part #17 11 1 460 759.
The valves in the cap won't function properly without it, no pressure and
vacum build up....as the fluid/vapour rather takes the easiest way.

Yes Charlie, there should be a rubber gasket there. Here's a pic of my old style cap compared to the newer style. 



The gaskets do tend to swell with age, as can be seen looking at the old gasket compared with the new one.

Paul.

thanks guys what I thought

I can easily hear fluid pumping back and forwards to the reservoir just by clamping the bypass hose with my fingers

I don't think that that should happen 

cheers again

ill try and make one today ...tyre tube rubber ?


oh  btw ..cleaned up now

The gasket is higher/thicker than the grove in the cap.
If you use a material that have the same thickness as the grove,
it could be that you don't get enough pressure on the sealing surface.

Charlie, I have a spare cap and a spare rubber gasket that's yours if you want it/them.

Crappy time of year due to gatherings/travel etc, but if anything can be organized, I will be in Bris Vegas on Christmas morning (Indooroopilly) if that helps.

thanks inge and blakey

will look around for something

no big rush I guess, its been like it as long as I can remember    or fell out one time and I didn't notice

trust bmw to build in a little trickery


cheers

mean while ready for a start ...but no go  yet ..checking stuff ...a can of "start you barstard " might be purchased today

grin

A new gasket is 2.5 mm thick, Charlie.

Cheers,
Paul.

thanks paul ...yep that helps

cheers