I am trying to add an oil filter (old style external Fram housing with C4
cartridge) to my M5 truck.  I described some of my agony just getting the
oil gallery plug out a few days ago.  StudeBob suggested that I use an
orifice to limit the flow to the filter so as not to starve the engine or
drop the pressure too much.  So, I found a nice little brass adapter at the
auto parts place that has 1/8 pipe male on one end, 1/8 pipe female on the
other, and a nice little .060 orifice.  Flow through an orifice is
proportional to the square root of pressure, so flow will increase slowly as
oil pressure builds.  A quick calculation suggest that this will limit flow
to about 2 gallons/minute at 40 psi, neglecting downstream pressure.  Is
this little orifice adapter the kind of thing that Studebaker used?

So, how much flow does an oil pump put out?  Tens of gallons per minute?  I
assume most of it goes back through the pressure relief valve at high engine
speeds.  With 30 inches of 3/16 o.d. steel line to the filter and another 18
inches back to the sump, will I be limiting the flow enough?  How much flow
should be going through the filter?

I never thought about the fact that, even on a bypass oil filter, you could
essentially have the full engine oil capacity go through the filter more
than once a minute.  Have I got this right?

Gary Ash
Dartmouth, MA
'48 M-5
'65 Wagonaire

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I forget where I read it, and I thought I had it indexed too, but can't find
it now.  I don't remember what the flow rate was, but you are essentially
correct. Stude part # 1549669 restrictor used about an .045" hole, same as
the hole in the oil pressure relief valve, but I believe your .060" will
work fine.


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The oil filter restrictor hole size is a # 50 drill. It should be
located at the fitting where the pressurized oil leaves the head to go
to the oil filter. In other words, the oil flow is restricted BEFORE it
gets to the filter. (See Page 25, March 2001 Turning Wheels.) BP