Oil pump losing prime / pick up tube air leak?

[Careful34]

Any one experience this kind of thing before? If I shut down the rig for more than a few minutes after the engine is hot, when I start it back my pressure gauge will read zero. If I leave it running like that the lifters will start to clatter after a few minutes. If I slowly rev the engine up, after a few seconds (usually) the pressure gauge will pop up to 30 or 40psi. Then it will stay there until I turn it off again. The problem is worse if I let the oil level get low. What it stikes me as is the pick tube having an air leak, or maybe the pressure relief valve sticking open some how. I opened up the pump and both the cover face, with single gasket, and gears still seem in good shape, I'm replacing the gears anyway. Any other ideas?

[porchpiggy]

Be sure and use the correct "paper thin" gasket, even a tiney bit thicker gasket will effect oil pressure.

[dshipley]

I had a problem like that about two years ago. I had it hauled home on a rollback. Cost me $75. I started working on it. Couldn't find anything wrong with the pump. So I thought it was a problem with the pickup maybe. I took the pan off and didn't find anything wrong. I worked on it and wondered about it for about a week. Then I put it all back together with fresh oil and filter. I put something on the old gears. Seems to me like it was Vaseline. I took out the distributor out and using my cordless drill spun the distributor shaft while my wife was watching the oil pressure gauge. To my amazement and deilght the oil pressure shot up to about 50 lbs. It happened to me once more when the oil had been in it for a while. I started the engine and the oil pressure stayed at zero. I stepped on the gas and it shot right up. I changed the oil, putting in a 10w40 or 15w50 synthetic blend, and as long as I don't leave the oil in an excessive period of time it works fine.
HTH