Engine guru question!
 

Hi knowledgeable crew!

friend of mine has 200 hours on a full rebuilt 500 efi, never went past 4k rpm except last week end
after keeping it around 4300-4500 for 2-3 minutes, oil pressure started to drop to close 20 on dash gauge in 5-7 seconds so he shut the engine off
put a mecanical gauge and did the test and read down to 27

so whats thr problem? Warming up opens up clearances? Where? I would of think it would become tigher with higner temps, not loose... suggestion?

Oil thins out as it warms up. Thinner oil = less oil pressure. Should have a bare minimum of 10 psi per 1000 rpm. Probably have some sloppy main bearing clearances. Disclaimer: I am not a Guru.

sloppy like too tight? Or too loose?

Sloppy means loose,,, like sloppy seconds.

did the oil pressure dropped to 20 psi after coming off plane or while at 4500 revs

Also, just to be complete, check oil level, as low oil level can show up at higher rpm as the sump (oil pan) gets sucked dry by the oil pump.

at 4500 after 1-2 minutes
back to normal when running 4000 rpm or less

it was leveled in the morning so i guess it should still be leveled 2 hours later but good point i will ask him

what is normal ? whats the swing from normal to 20

when it start to drop in takes like 5-7 seconds

What viscosity oil?

what Im asking is the psi that you refer as normal before it starts to drop, what is the oil temp at this time ? big heavy boat ?

If you’re definitely full, you could try running a lower level. Might be whipping up a froth at high rpm.

between 50-60 psi
no idea about oil temp
it in a 38 sonic

2 weeks to go for boating season so
will take it out and have clearances checked to rule that out

When apart, Make sure any windage tray or rear baffle that is supposed to be there, is there. Also head oil drainbacks aren’t being blocked partially by anything. And pump screen to pan clearance.

I think you need to do more testing, rule some things out before just saying we're going to pull it out, so its a twin application but the other engine that was not rebuild is ok ? call the shop and get the specs on the bearing clearances, was the crank turned in the rebuild

Remove oil filter and cut open, if it looks like Christmas in the filter you have junk.
if clean filter, let her eat.
Good luck.

When apart, check oil pump pickup tube/foot for being cracked or loose at the oil pump. Could be sucking air when oil level is lower due to being up inside engine.

I would try to answer but the explanation of what is going on leaves my head spinning.

Good call to drain and check the oil for debris.
Pickup tube come off?
Debris in pickup
Bearings

Thicker oil may help with pressure, but it's just masking a problem if oil pressure used to be 30 higher.

Curious to hear what the oil and filter look like.

Had this happen to me after a rebuild, had the motor apart multiple times, then found the oil lines were reversed to oil cooler, would show at high rpm and cook the oil, pressure was no existent when I got that hot. Worth a shot to look at, also on boat like that, I would figure there are oil temp gauges, if there are you temp readings should be off motor to motor or at least pre/post rebuild if the lines are wrong.

20-50