Oil pump bypass spring ??

[PRHeads]

My experience with the stuck bypass valve was the result of a very small metal shaving getting wedged between the pump body and the valve……. Resulting in it being stuck in the fully closed position.
This was a 340 with a Melling M72HV pump.
The result of that was a hot idle oil pressure of about 120psi.
It instantly pegged the 100psi mechanical gage, and the needle never moved.
I ended up attaching a 300psi gage to the engine to see what the pressure actually was.
(You won’t believe how high it would get when you revved it up)

Pulled the pan & pump, pulled the pump apart, found the issue, put it back together……… no more 120psi hot oil pressure.
I don’t recall what that was(30+ years ago), but I don’t remember it being strangely high.

So, my experience is that with the bypass valve completely shut, the hot idle oil pressure was about 80psi higher than when the bypass valve is functioning.
My takeaway from that is the bypass valve is “bypassing” some amount of oil anytime the engine is running.

So, a stiffer bypass spring will keep more of the bypass hole closed off at any given rpm.
Less bypass area = more psi

 

[rickseeman]

I've started 2 383's that were stuck. Neither had an oil pressure gauge but it wouldn't have mattered because it would have been off the gauge. In both cases first it ballooned the filter (one was a NAPA Gold) and then it blew the oil filter gasket out and dumped all of the oil on the floor. Both of them were original 56 year old 383 oil pumps.

 

[Daves69]

My experience with the stuck bypass valve was..........

FWIW, mine was on my '77 360 Ramcharger daily driver way back, early '80s. One cold morning I started it up and seemed fine. As it warmed up the oil pressure dropped off considerably. Shut it down checked oil level which was fine and no shiny particles on the stick. Restarted and pressure came up but not even a third of normal, so I just shut it down.
It had a little over 100k miles, so I decided to change the pump.
Just as soon as I broke the first pump bolt loose, I heard the relief pop closed.
No way I was reusing it though. A new pump went on and it was fine for another 35k miles when I traded it in for a '89.