When I first did my vanagon conversion (2.0 I4 at 55 degrees using diesel
parts) I had a problem with the oil pump losing its prime.  This first
occurred after sitting in my mechanic buddie's yard for two weeks waiting
for the AC retrofit.  Being that I taken a brand new 36mm oil pump, and
replaced the top half of the pump with the diesel pickup part, I figured
something was amiss with the old pickup assembly.  After sorting out an
initial issue with oil pressure fluctuations (solved with a 2.0L windage
tray) I had swapped in the stock diesel Mann oil filter.  I had searched
these archives for oil prime issues and one of the posts suggested the
filter might be an issue.  Well the problem hadn't returned since then
(last year).  After about 5000km of breaking the engine in, I replaced the
oil with synthetic, but used the smaller gas 2.0L Mann filter.

So yesterday when I tried to fire it up for a winter warm up (after sitting
in the garage for 5 weeks or so), no oil pressure.  I shut it down after a
few seconds, and tried twice more.  Still no oil pressure.  Today I went
out to pull the distributor and prime the engine, but first, on a whim,
swapped the diesel oil filter back in.  I figured it was worth a try as I
can see definite differences in the anti-drain back mechanism.  I turned
the engine over and about 2 seconds later, full oil pressure.

So my theory here is that either the filter itself or the anti-drainback
valve is more restrictive on the Mann gas I4 filter.  Given the extra
length of the oil pickup on the diesel, one wonders if the diesel type
filter is designed for less restriction/easier prime.  It holds likely
twice as much oil as the gas version which was my original motivation for
using it.

In short order, I'll be installing a 1 litre accusump pre-luber which will
resolve the issue permanently.  I'm still not comfortable with the one or
two second delay in seeing oil pressure on cold starts.

Any experts on the diesel oil filter here?