2000 dodge ram 3500 flatbed. We rebuilt the trans. back in december, this guy has been a good customer. Comes back and says check gauges light comes on and his oil pressure gauge drops. Check and it physically loses pressure after running for a length of time. We have changed the main bearings, rod bearings, oil pump, and the pick up screen. Put it back together... same damn thing. Cold it has the right pressure as it warms oil pressure slowly drops back down and eventually to 0.

If you give it some gas oil pressure goes back up. Truck sounds like it runs good when cold or when under throttle no tapping, When it loses pressure the right side(pass.) of the engine seems to tap which is right where the pump puts oil back to the top of the motor.

Any Ideas???... Did we buy a bad pump out of the box? I'm being told cam bearings but if that were the case than why do I have oil pressure when cold or under throttle. I can't see that as being the case, it just seems like the oil pump isn't doing its job.

 

Have you verified the oil pressure with a mechanical gauge.

Is the engine full of oil?

What weight of oil are you using?

sounds like it's bleeding internally somewhere.

Is there a gasket anywhere in the oil pump/pickup?

 

Yes, cam bearings can cause you to loose oil pressure. Old, or worn bearings cause a "pressure" leak which will cause a drop in oil pressure. The pressure is good when it's cold because oil is thicker when cold, as the engine heats up, the oil thins. But to go all the way to 0 is really weird, though. Check ur cam bearings, the weight of oil, and make sure ur mains are all torqued down to the proper lbs.
Good luck!!