Lost oil pressure @ high RPM

[rksboat]

Sorry for long post. I have a 2001 280ss Formula with twin 350 Mag MPI, 360 hours.

First time alarm sounds @ WOT I back off throttle looking at gauges for problem, alarm goes off, I never saw anything on gauges, went on with the rest of our trip with no problem running 3200-3400 RPM. Took out to test a few days later running about 4200 RPM and again alarm goes off noticed 0 oil pressure on starboard engine shut down immediatly, no noise from engine. Started back up after checking oil. Oil pressure comes up to normal and continued back to ramp at normal RPM with no problem. Took boat out with mechanic, hooked up mechanical gauge. After running 4200 + RPM for a few minutes mechanical gauge fluttered then dropped to zero & alarm sounds. (same symptoms as dash mounted gauge) Again shut engine down checked oil, restarted after a few minutes, oil pressure comes up to normal. Ran back to ramp with no problems. Changed oil & filter still same problem. Decided to repace oil pump. Pulled engine dropped pan everything was clean. Took out to test replaced oil pump. 20 Minutes into test run for starboard engine my port engine does the exact same thing. This time I was running at 3400 RPM and hit a very large wake. Just after we hit wake gauge began to flutter then droped to zero. We pulled engine and replaced oil pump in that engine. Again port engine oil pan clean. Take out for test run with two new oil pumps. After running about 20 minutes at normal RPM I took up to 4000 RPM. Within about 1 1/2 minutes both engines lost oil pressure, (about 10 seconds apart) Again shut down, restarted after a few minutes and ran at normal RPM for over an hour with no problems. We have since pulled the valve covers and intake manifold to check for blockage. Everything is spotless. Plan to disconnect remote oil filter on port engine and install filter directly to block. Dipstick shows full on each engine but may add more oil to starboard engine to see if either of these solve problem.
Has anyone run across this problem before? Any other ideas?

Thanks,

Rich

 

[PuddleJumper]

Re: Lost oil pressure @ high RPM

WOW You've spent a lot of $ on this problem. Are you reading the dipstick with boat on lift/trailer or while sitting in the water? You may be overfull and getting an aeration condition in the oil. You might try sucking out some oil so dipstick reads in middle of "safe range". Can't hurt and won't cost much to try.
Good luck.

 

[rksboat]

Re: Lost oil pressure @ high RPM

Checked oil level in water. We have changed oil several times during this process. They currently have 5 quarts and show full on the dipstick. Engine manual shows 5 1/2 qts w/filter.

 

[n2ostroker]

Re: Lost oil pressure @ high RPM

Cut the filters apart and look for bearing material. Unfold all the pleats and see what you find. If you lost oil pressure at ~4500rpm it probably ate some of the bearing. The rods, mains, and cam bearings will hold pressure till the oil gets hot and then pressure will fluctuate or drop. Then after you shut down and sit for a few it cools down and has pressure again. The cam bearings can run dry real quick and will kill oil pressure cause it just sprays out.
I had the pickup drop out of the oil pump running about 5krpms. Oil runs real low in the pan and pressure dropped to nothing. It ran for a few seconds that way. When I pulled the motor to check things out I wound up cleaning up a few rod journals and replacing all the bearings and measuring all their clearances. I'm sure my cam bearings need replaced but that'll be a winter project.

 

[rksboat]

Re: Lost oil pressure @ high RPM

Is the bearing damage a possible cause of my problem or a result of no oil pressure?

 

[dr_bowtie]

Re: Lost oil pressure @ high RPM

pull the oil filters and then pull the adapter plates and check the bypass springs...

if they get weak or broke it bypasses all the oil right back to the pan...

 

[FreeBeeTony]

Re: Lost oil pressure @ high RPM

Are you using high volume oil pumps?

 

[wca_tim]

Re: Lost oil pressure @ high RPM

My first thoughts are along the same lies as yours - that you're running out of oil in the pan as in it's holding up somewhere. all the bearing problems mentioned would let oil pressure fall to nothing at idle anf if it were bypass issue it would flatten out but not drop to zero. Have you tried taking pressure off the port on the front of the block? can give you some idea of how much pressure is being lost in the bearings..

Did this just suddenly happen? what changed between when you could keep the hammer down without problems and when BOTH engines started having apparently the same issue. did you change oils? oil filters? crankcase vent or evac set-up?

 

[rksboat]

Re: Lost oil pressure @ high RPM

Did this just suddenly happen? what changed between when you could keep the hammer down without problems and when BOTH engines started having apparently the same issue. did you change oils? oil filters? crankcase vent or evac set-up?[/QUOTE]

Nothing changed. Oil and filters changed last fall @ winterization. No problems for first half of this season. Just happened suddenly as I said in my OP. Only other common thread is during this process we found both engines had manifolds leaking. I have replaced manifolds and elbows on both engines but problem started before that.