I have a twin engine 500EFI boat rebuilt last winter. Both oil pump housings and gears looked great after pulling the covers, so I reused them.
Have put about 15 hrs of various driving on both engines and they seem to run great. During the first 3-4 minutes running, both motors maintain 60+ psi. Then the starboard motor will drop down to 38-40 psi while the other stays at 50psi. Come down off plane to idle and the starboard drops to 25 psi and the other 40 psi. Idle around for 5 minutes and the lower one comes back up to 50psi. I'm worried that 38psi might not be suficient pressure for 5300 rpm.

This lower oil pressure is driving me crazy. Can anyone shed their thoughts on this? Thank you!


Engine water temp= 155*
Engine oil temp = 170*
Mobil 1 15w-50 oil
FLORIDA air temps

Check your oil coolers for restrictions. Had a similar issue this year and one cooler had debris in it. Rod them out and ensure water flow/pressure is sufficient.

When you did the rebuild did they plastic guage the main and rod bearing caps when they assembled the motors to inspect for oil clearance between the bearing and the crankshaft ?
What was the oil pressure before the rebuild ?
It is always good practice to toss in new oil pumps when your that deep into the motor.
The water temps in Florida are warm to begin with which makes the motors run a little warmer !
You could check the oil pressure with a mechanical guage to rule out the possibility of a bad sender or guage.
Good luck , let us know what the problem is when you find it !

The oil pressure before the rebuild as I recall was consistant with both motors. Bearings looked OK in both main and rods but I replaced them with new anyways. Did not plasti guage the mains and rods. The old bearings looked like they did not have much time on them and everything looked real good.

So you didnt measure bearing clearances during rebuild?

If it were a bearing clearance issue, I'm thinking the oil pressure would be lower all the time. What ever it is seems to triger after the engine is run past 3000 rpm for a period of time. (I'm guessing heat related)

First thing would be to verify oil pressure with a mechanical gauge.

Thanks Griff - I'm gonna check it with a mech gauge next time I take it out.

im not trying to come off as an azzhole BUT,assembling an engine without checking EVERY bearing clearance is as smart as playing russian roulet.

Check with mechanical gauges to be sure what both are.

I don't see it being a clogged cooler if temps look good on oil temp gauge.

Low pressure and loose clearances are going to result in a failure soon I would be surprised if that has not happened yet if that's the case...
Plastigaue isn't better then nothing but mikes are best and more accurate, like mike said to not check that is opening up for disaster might be ok, might not be, always use new oil pumps no matter what not worth saving money there...

Oil will thicken back up increasing pressure as it cools off... That's why pressure returns... I would be looking at places it's bleeding off... 50 to me running is not a lot and scares me but that's my opinion..clearances come in to play big time with what's acceptable and not. But 38-40 is not enough if it's accurate