Okay 502 Gen VI,dropped a valve seat,Engine builder 1 sleeve,couple new pistons,light hone.Came back looking like new.Installed in boat.Its the port engine.Oil pressure starts out at 47 at idle fluctuating down to 20 and erratic,fluctuates 10 to 20 up to 47 after about 10 min cruise 3500 rpm.After 20 minutes pressure drops to about 5 and stays there,occasionally rising to 25 erratically.Seems to have to much crankcase pressure.Small oil leaks from lots of places.Had Moroso push in breathers now have 1/2" into the arrestor.Oil filter is fitted to the pad and using the factory oil cooler lines.I know you "can't do that in a boat"Its worked for 4 years.I have changed senders,tested the gauge and sender cable.Could it be pump or pick up related?I've ruled out the lifter valley plugs but i'm open to whatever input i can get.I plan this week to change the filter,oil and check the bypass valves in the pad.Then i pull the intake to check plugs.Then the pan.

Did you use the same oil cooler on the refreshed motor?

Yes i did.Great idea.Thanks

I had similar problems with my mk4 big block but it was due to oil galleys being bored into during the machining process. The main oil galley on mk4 blocks run along the oil pan rail. I believe the mk6 main runs along the cam tunnel and would be impossible to compromise.

If all this occured after the engine was freshened, I would pull the engine, tear it down and inspect everything. If it was run with a TRUE reading of 5 psi, then there will almost certainly be galled bearings. The point is not to cause any more damage

My suggestion would be to put an oil filter on the engine pad like it was being run in a car, and put a MECHANICAL oil pressure gauge into the sender hole. This will eliminate gauge error. Use an oil primer tool to spin up the pump. If it shows a consistant reading of 20-40 psi, then run it using the same gauge setup (you may need an assistant to watch the gauge)

I use remote mounted oil filters and I know if the in and out lines are reversed, this will cause erratic oil pressure.

If an oil galley plug is left out, this will cause zero oil pressure.

If the block wasn't cleaned and prepped properly before assembly, there might be an obstruction in one of the passage ways.

I know how frustrating this can be and a lot of my frustration was spared by using an engine run stand before I installed the engines. I bought an engine cradle from JEGs (60.00) and fabricated an instrument panel from my old gauges. Used clear tubing for the seawater pump and a large metal tub to pull water from.

Hope this helps, Casey

Many people do not like using the oil cooler that was plumbed when a motor goes bye-bye. In the very least, it needs to be thoroughly cleaned, but getting all the contamination out is not assured, and there are many who would not even risk the possible damage, for the price of a new oil cooler.

I wouldn't.

Inspection of the bearings is indicated by the low readings you had, and I would suggest that even if you can find no bearing damage, that you replace the oil cooler.

Thanks for the input.I will take it all aboard.I can't understand why the pressure starts off at 47 and drops so low.Obviously as the oil is heated but it is too large a drop.Then theres the fluctuating before it drops and stays low.

What does the oil filter look like when you cut it open? Could be a pick-up......could be a venalated piston (crankcase pressure) or a spun bearing somewhere.......which is what it sounds like...

Haven't cut the filter open yet but will let you know when i do.I was thinking pick up problem.Motor seems to run fine,not down on power.If the pick up is loose and it sucks air,oh sh*t i don't know, like i said its driving me nuts.I just going to have to go and start pulling it apart.

Possibly a defective pressure relief in the oil pump?

I'm guessing there was some metal left in the cooler, which got into your bearings.