Do we have oil filters with a non return valve?

[Mordan]

I heard Volvo has them to keep oil in the tappet/lifters.

[shogun]

yes, see here the problem
http://web.archive.org/web/20040604075404/www.e32fixes.com/results.asp?method=show_fix&fixid=5
also on the M60 engine there is a known problem that the ball gets smaller and smaller and finally might disappear. The new oil filter for the M60 has a different material.

[Russell]

I do not think the M50 has this sort of valve?

[bubba966]

I do not think the M50 has this sort of valve?

Yea, it's in the filter canister not in the filter.