Fram w/anti drainback valve?!

["Luis A. Marques" <marques@ti.com>]

All this talk about oil filters prompted me to open an extra Fram
filter to see for myself how horrible they are.  To my
surprise, although it didn't have the anti-drainback valve in the
usual location, it did have a piece of rubber shaped like a flat
donnut covering the holes where the oil flows in.  It was placed
there in such a way that it serves as a check valve, allowing the
oil to go in but not out. Could it be possible that the Fram has
an anti-drainback valve after all???

Is this flat rubber donnut thing something all filters have, or is
it just a simple, cheap implementation of the anti-drainback valve
used only by Fram?  The filter No. was PH2870A and was supposedly
made in the USA by Allied Signal if it makes any difference.

In defense of the Mann and Mahle (and Amsoil) filters, its
construction left something to be desired.  The filter media was
made of what appeared to be paper/carboard.  It was pretty thin
also: less than 1/16".  The ends of the filtering media are made
of cardboard and there is a pressure relief (bypass) valve on the
oposite site of the threaded end.  Overall, it seems like an OK
filter to be replaced every 3k mi., but I wouldn't feel comfortable
leaving it in place for any extended period of time.

Luis Marques
'87 4kcsq