Oil pressure problems!
 

Ok, my friends 540 just had the lower end gone through. New crank and bearings. A Moroso high volume pump was used. Oil pressure is good when first started runs up to 60psi at speed, come off plane and at idle it drops to 0 zip nothing. What the hell is going on here? It is almost like the pump loses its prime.

Shut it off and restart and it climbs up again.

Maybe pick-up tube came off pump. Full pan, pump is below the oil line.

I am positive it is welded

What oil filter are you using ? A couple guys here have had filters fail and cause a lack of pressure in the past few months .

Not my motor but the same guy built my old motor and he used napa/wix performance filter.

Well that's a great filter . I would check to make sure , always check the stupid overlooked stuff first .

that was the first thing I told him to do...change oil and filter.

It was welded, I have seen them come off before.

Pick up is off or the pump was never tightened to the main
cap. Pull it apart before you hurt it. Cut filter open and if clean you should be ok.

Thanks for the advise, I just want to stress that this is NOT MY MOTOR once again as I have a boat for sale here in the classifieds. Jesus, no good deed goes unpunished! This motor has a sister motor in a big tub powerquest with an interweb retarded owner.

What is being suggested does not make sense, how does the pump still make pressure under high rpm when oil is low in the pan and in the upper end?

Was this pressure drop verified with a mechanical gauge ? Could be as simple as a bad sender .

Deep, yes it was verified with Mech gauge.

The pressure regulating valve in the oil pump may be hanging open or moving sluggishly . This would explain why shutting the engine off and restarting it see's a return of pressure . Stranger things have happened .

Man sure sounds like a filter problem that I had with a Fram that sucked down to 0 turn it off restart fine go a minute suck back down to zero.Replaced the filter all was fine But that was that old crappy Frams they were selling with the valve in them that would not allow the filter to drain so you did not have a dry start after setting .

Seemed like a good idea at the time but it failed.

Could be the pressure regulator valve in the oil pump or maybe the oil pump has been grooved by something in the oiling system.

^^I think this is the problem^^

What's the pan capacity? If it's a standard five quart pan it's pumping the pan dry. Standard pump it's all good, move to a high volume pump, another story. Had the exact same thing happen in a jet boat years ago.

I will find out the pan capacity.

If your not careful welding the pickup on the oil pump, you can overheat the spring in the pressure valve and cause it to fail to close the valve properly. Is there a 'TRAP' in the pan sump. Maybe door is not working and the sudden acceleration causes starvation. Pick up too far off bottom? Filter adapters often have a bypass in case the filter fails and it's spring loaded (I plug them with a 1/4" plug)

So many "little" things can screw with oil pressure it can drive you nuts.

What is oil temp?

Update...lines were swapped on the oil filter.

That'll do it! Glad you updated the thread to let everyone know what the problem was.