Oil Pressure Issues

[whty8911]

My boss has a 2002 Sea Ray 360 I believe. i do know the motors are 2 - 496 ci Mercruisers. One engine has had repeated oil issues for awhile now. The initial problem would occur if you throttled the motor over 3500 rpms. The oil pressure would drop from 45-50psi to 20psi and the alarm would sound. After a lot of back and forth the motor was pulled and a machine shop found excessive tolerances in the crank bearings. The motor was rebuild with new bearings and a few other things. The motor primed fine at first but after running the boat the motor is now worse off then before. 5psi oil pressure is at idle and may or may not jump to 20 psi before the system shuts the motor off. The gauge and the sending unit have been replaced nurmerous times and the motor is now running on a mechanical gauge. The oil cooler system has been bypassed to eliminate that as an issue. And no external leaks could be found. The low pressure was no there immediately but took some driving to get it to occur but is now consistent. Any ideas.

 

[JediJD]

Oil pressure on an 8.1 is only a function of a couple of things...

1. a clean oil screen so that oil can get to the pump
2. an oil pump with proper clearances
3. proper clearances on the crankshaft bearings.

Assuming your gauges and oil viscosities are correct...one of the above isn't.

 

[stuckinforward]

i would assume the oil pump was also changed, did they pull the cam and inspect?

 

[whty8911]

All bearings were replaced cam and crank. Along with a new pump and screen all from sea ray. A little something I found out last night. If you start the motor cold, it has 40 psi pressure. When throttle is applied and you cruise for about 500 meters pressure drops off and motor rattles and knocks then shuts off. According to another source, a friend that was present at the time, the motor has a knock to it at higher rpm which occurs while pressure falls.

 

[JediJD]

There was a great line in "Atlas Shrugged" that went something like this..."We live in an orderly universe which cannot support contradictions. If you have an apparent contradiction, check your premises. One of them is incorrect."

The fact that something was done, doesn't mean it was done well. I don't know enough about your configuration to tell you if it makes sense to R&R oil pump as a test, but if I were in your shoes, I'd be headed for a tear down thinking someone didn't torque properly or plastiguage my main bearings and HOPING that there was an install problem on the oil pump pickup.

Edited: Your edit convinces me-main bearings. Just as an aside, this is almost a poster child for the reason people buy remanufactured instead of having parts replaced.

 

[stuckinforward]

if you attack a problem such as this, you must keep in mind that oil pumps dont create pressure, restrictions do, and somwhere in that engine you've lost a restriction, i.e main bearings, cam bearings, oil pump, worn crank and to the likes....a fix like this i could imagine at the dealer would be for them to throw in a high volume pump or just run it until something happens,or even a jug of Lucas, well, we know thats not the solution, something was overlooked and not checked and you have what is considered an internal leak.
I love when these guys who build engines start yacking about what they got in there....4 bolt mains, high volume pump, this, that, this, that.
and then my questioning starts, why a high volume pump??? to me i say it robs HP, no benefit...why 4 bolt mains? so you dont lose a crank? Ive never lost a crank...the 4 bolt mains are for block twist, thats it, sorry for the tangent but, I think I do more engine because of another parties mistakes and this situation seems to fall in that catagory

 

[Ididntdoit]

Ya - like the replies infer above - the machine shop screwed up - Its now worse than it was, sounds like he probably spun a bearing - It will cost even more to fix than the first time - nothing wrong with rebuilding an existing motor, just make sure the machinist knows what he's doing