looking for other opinions here.454 in a jet boat.started doing this end of last year.runs fine for 10-20 mins then oil pres drops and lifters start making all kinds of noise.starts with 60 psi oil pressure then drops to @3-5 psi.7 qt oil pan stock melling oil pump and screen,new crank,rod and cam bearings.did this with old bearings/oil pump and new bearings/pump.everything looked fine when taken apart and went together fine.this used to be a truck eng so im not sure if the oil bypass has been replaced.may have an automotive bypass in it still.could this cause the concern?checking oil pressure right above the oil filter on the side of the block.ideas?using 10-40 oil and has no oil cooler.water temps @160

Are you saying after a run, the hot idle is 3-5 psi, or while running under load it's dropping to 3-5?

If its doing it under load, it could be that you are sucking the pan dry, do you have a screen in the lifter valley? Have you pulled the oil filter and cut it open? I would think you would you have damaged the bearings from this happening.

Oil bypass shouldn't matter if you aren't running a cooler. But you should be running a cooler on a BBC in a marine application. Did you measure your bearing clearances on reassembly?

last year running @ 3000-3500 easy cruise would be fine then pressure would drop,lifters noisey.no screen in lifter valley.engine ran fine most of last season then this problem just showed up.oil pressure would come up some after it idled for a bit but once it was warm it would drop fast.has a new stock melling oil pump and screen. extra capacity pan same as last year.so far have only ran it on the hose not at the lake.doing same thing as last year.

This is an important detail, and very well could be the cause of your issue so I am going to ask again.

unfortunately I did not put the crank in(its a friends motor) so I do not have that info.i do know that it did the same thing as last year.it has new bearings and the crank was polished so I don't know what size bearings or the clearance.there was no metal in the oil and the crank looked good when it came out.i know this is vague info and its hard to figure out without all the facts but im just trying to rule out something simple that I may be overlooking.

Running under load with 3 psi of oil pressure doesn't end up with the crank looking good and no metal in the oil, so something else is going on.

excessive bearing clearance would be my guess.once i put standard bearings with a .010 under crank,pressure would drop to 5 lbs as soon as oil got a little heat.i pulled the pan and installed the .010 under bearings and all was good.

ok thanks for the replies.looks like I will pull the motor and check the clearances.one more question for opinions sake,what kind of clearance do you guys run between the oil pump pick up screen and oil pan?

Verify pressure reading with a mechanical gauge also.
Try using a quality straight 40wt oil.

If the pressure readings are correct, then I'd say its too much bearing clearance