Philip,
The anti siphon valve is frequently referred to as an anti-drainback valve
and roadster owners should be aware that it does not take the place of the
tube in the center of the filter housing. The anti-drainback valve prevents
back-flow towards the oil pump when the engine isn't running. The tube
prevents flow the other way out of the filter-towards the oil galleries
(except oil above the top of the tube). If you want your filter to be full of
oil when you start the engine (and you should) you need both!
The anti-drainback valve is quite simple-just a flap of rubber or silicon
that you can see through the small holes surrounding the threaded hole on the
bottom of your filter. Oil enters the filter through the small holes and
exits through the center.
Since the u20 and r16 have a bypass built in it seems unnecessary to use a
filter with a bypass. I don't think the OEM filters had one.
David Urschel
srl311-10465
Philip Erickson wrote:
> There are two types of valves fitted into the filters, anti siphon and
> by-pass. The anti siphon keeps the filter full of oil, like the long tube
> in the center of the 2000's filter fitting, and the by-pass allows oil to
> by-pass the filter if the pressure drop across the filter is too great
> (clogged filter).
> NOT ALL Filters have both features in the filter and the pressure drops
> vary according to engine design.
> If you install a filter with too low of a by-pass pressure you could get
> no filtering at all, if you install one with too high pressure you may get
> low oil volume.
> A Ford filter ( PH8A ) is a common aftermarket general use filter, I think
> it has both features.
> Phil
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