Gen VI 454 oil pressure at idle 65# at rpm 95+# this started all of a sudden with no changes done at all. Is it possible for filter bypasses to have any part in this? mechanical gauge installed in port above oil filter pad.All ready changed pump thinking possible relief valve stuck closed ,no change,plenty of oil at rocker arms,with priming tool and drill 65# pressure.

Its most likely not the bypass if the filter is new. The bypass only comes into play when the filter is restricting flow. Check your gauge.

I have used 3 different gauges. Installed 1 at remote filter location before and after filter change. no change in psi.Starting to think about possible restriction in block, but plenty of oil to rockers?Remote dual filters as it came from factory nothing changed or added.

wrong relief spring in the oil pump!

did you get 2 springs with the oil pump? you may have to pull the engine again and replace the spring,,

a few years ago i had a 598 in a boat that spun a rod bearing and the oil pressure was oe 45 psi at idle and about 65 at wot,,went to 90 psi rite before i put a rod through the lifter valley

only 1 spring no extra 1. original pump looked fine,relief valve was not stuck or scored. This issue started all of a sudden,ran great as usual ,turned off restarted about hour later oil psi pegged gauge.motor sounds good no new noises.

Just asking by chance are you using a Fram oil filter non HP version ? If so get rid of it use a Wix or a Mallory Marine inwhich Wix makes all their oil filters for them. A lot cheaper than the Merc oil filters. Also Amsoil makes a damn good oil filter.

I have seen Fram oil filters peg oil pressure gauges - change them out and pressure back to normal. Fram cheap inners have Cardboard end caps collapse under higher rpms. Cut one open and you see how cheap they are. All quality oil filters use stainless steel end caps.

Melling oil pump ? you can call them and ask for George over their for some info / help. I also think maybe your problem might be the dual oil filter set up. keep in mind your bearing clearances has alot to do with your oil pressures and flow along with your viscosity / weight of oil your using.

wix filters dual setup has been on motor since new.ibelieve oil press sending unit location is after filters and bypass valves in block.possible bearing moved causing restriction?

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I believe you may be on to something, if a main spun even enough to cover the oil hole that could cause a sudden spike like you're seeing. Saw this once before in a small block, I told the guy then he had an internal blockage. He didn't believe me, couple of days later the motor was toast. Once all the bearings are spun, it's difficult to find the culprit.