Posted by Chewie on Monday, June 16, 2003 at 4:49PM :
In Reply to: Dose anyone sell the full flow oil pump? posted by Willy-N on Monday, June 16, 2003 at 2:13PM :
By Pass Oil FIlter Clarification (Long Post)
Just want to point out some misconceptions about the bypass oil filters
commonly found on our flatheads. I've heard a lot of these misconceptions and
also have seen a lot of the filter units incorrectly installed. They are very
good filtering units. In fact, on the micron level they can do a better job
then
todays full flow filters. First, a common statement is they don't filter all
the
oil. Not true. If you look on the driver side of your block about 10" down from
the head you will see a ridge in the block that runs the horizontal length of
the
engine. This is the main oil gallery, fed by the oil pump in the center. You
will
also see 5 plugs which are the location of oil feed lines to the main and cam
bearings. This gallery carries oil from the pan, via the oil pump, under the
pressure noted on your oil gauge. In fact, if you follow your oil gauge line
you
will see it leads directly this oil gallery. A properly installed supply line
to
the bypass filter will be fed by one of those plugs. It's under full pressure,
directly from the oil pump and comes out of the same "pipe' or gallery feeding
the mains and cam bearings. The oil is pumped through the filter and now
needs to return to the pan. Now comes the "bypass" part. The correct location
for the filter return line is the plug directly above the oil pressure relief
valve. It's on the horizontal "shelf" that pokes out. In fact, if you take the
plug
out you can see the pressure relief valve. The "bypass" is at oil pressure
relief
valve. When oil pressure is normal, say 40 pds, the oil pressure relief valve
move out against a spring. On the valve is a cutout that when it reaches a
certain point a passage opens for the returning (clean) oil from the filter so
it
can flow back to the pan. So oil only returns from the filter when oil pressure
is as a safe level. If pressure falls, the valve closes and the filter is now
out
of the circuit or bypassed. This helps maintain oil pressure to the critical
main and cam bearings. That way only clean filtered oil is returned to the pan
when the engine is at a safe oil pressure level. Don't let that small line size
on the filter fool you. It is moving a lot of oil when the valve is open. I
cracked
a 1/4" line in my truck and lost 3 quarts in little over a mile of driving.
Remember it is under the same pressure as the entire oil system. And all of
the oil in the pan gets filtered. Todays full flow filters are set up to feed
oil
directly to the engine mains under pressure. If they clog up your mains are
starved and you have an engine failure. That is why all full flow filters have
a
bypass for when they clog up. Oil flows around the filter instead of through
it,
but the oil pressure and flow is maintained to the mains saving the engine. The
problem with full flow is the volume and pressure of oil moved. Look at the
size of the inlet and outlet holes the next time you change a full flow filter.
To achieve this volume the filter does not filter to the same micron level as a
bypass type system. It's not unusual to see on ling haul trucks a bypass system
in conjunction with a full flow system. So remember, a bypass filters all the
oil in the pan, does so when the engine has adequate oil pressure and is a high
quality filter.
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