0 oil pressure any ideas

[Blue Thunder]

Bob,

I agree with some of the recent posts. I don't think you have the big problem that you think you do. What you are describing for oil pressure is right where my 1985 Liberator 5.7 Mercruiser was for years. After I gave it a "hot supper", the lifters would clatter a bit too. Those Mercruiser Chevy 350's with 4 bolt mains are nearly bulletproof if you take care of them and it sounds like you do. It's your boat, do what you want but I don't think you need to repower it. JMHO.

BT

[Sunset Bob]

Originally Posted by Blue Thunder

Bob,

I agree with some of the recent posts. I don't think you have the big problem that you think you do. What you are describing for oil pressure is right where my 1985 Liberator 5.7 Mercruiser was for years. After I gave it a "hot supper", the lifters would clatter a bit too. Those Mercruiser Chevy 350's with 4 bolt mains are nearly bulletproof if you take care of them and it sounds like you do. It's your boat, do what you want but I don't think you need to repower it. JMHO.

BT

Yes maybe I am a little to critical but its my nature.I am a FAA licensed aircraft mechanic.I am going to run the boat some more and see how it acts before I take out any guests.
And not like I want to spend the money but this boat will fly with a new Mag 350 OOOps there is that darn speed limit.

[VtSteve]

I had an 1994 Larson, small bowrider with the little puppy engine. Not sure I could have made it to the magical number. One thing to add. I have no idea if you've got an inclination to look around. But I've seen deals on new boats this year that really made me look seriously. My boat is an '06, so not great timing. But when I saw a pretty loaded Chap 250 cruiser going for $51 out the door? The used market is dead, even deader than the truck market. 2008 models are as cheap as new boats get.

[Winnipesaukee]

I'm what you call a "shadetree mechanic."

Here's what I think is going on.

In your crankcase, there is a spring-loaded piston that regulates oil pressure. Ideally, when the engine revs, this piston springs up, allowing the pressurized oil to bypass the "system" and redirect into/through the crankshaft, where it "seeps out" directly onto the crankshaft/conrod bearings. This action simultaneously regulates the oil pressure and lubricates these crucial bearings (keeping a film of oil between them and the crankshaft).

Every time you start your engine, these bearings wear a little more (get thinner) because there is no pressurized oil preventing them from touching (this is slightly different than "lubricating, where the parts actually touch"). Eventually, they wear so much that the space between the bearings and the crank grow so much that the oil "seeps" fast enough that the oil pump can't keep up.

This would fit your symptoms if the oil pressure relieve assembly (which I think Acres Per Second touched upon) or the spring was worn/damaged in a way that left it stuck open after running the engine for a period of time. This combined with the worn bearings would explain your problem.

One way to test it is to rev the engine (3000rpm) for a few seconds after the drop (do so at your own risk). If you get pressure again (pump is working harder at 3k than idle and may be able to overcome the extra volume loss), then I'm most likely right.

What can you do if that is the case? Run high viscosity oil. Viscous oil can't flow as fast and cannot "seep" past the crank bearings as fast. Try changing your oil with something like 20w-50 and that will extend the life of the engine a bit.

Oh, and get Seatow.

Hope that helps a bit. Best of luck. If you have any questions, post it up here or PM me.