I have a 2000 4.2 rebuilt motor.
I am on the second motor from the builder. I marked the block 1st rebuilt motor when I had them pick it up. So I know i didn't get the same one back.
The problem is as follows:
Sitting at a stop in drive. No accessories on. The pressure is up and stays there. I can either turn on the a/c or crank the steering wheel all the way to one side (to create a draw on the motor). After about 2-3 secs the oil pressure drops to 0. I turn off the a/c or let off of the steering wheel (to release the draw on the motor) and 2-3 secs later the oil pressure will come back to normal.
I have replaced the oil sending unit. I have taken the sending unit out and installed an external oil gauge to witness the same. This way I could tell if the gauge on the dash was working or not. Both would drop at the same time. I have not let the van sit long enough to witness any lifters going dry. I have only let it sit for about 5 secs with the gauge(s) on 0.
I have been told to check the piston/check valve where the timing cover meets the oil pump. Our mechanic says he replaced it when he put in the first and second motors.
I can only assume that someone else has run across this before.

Any help with this gremlin would be appreciated.

Robert P.

 

I had that problem on mine. the gasket wasn't installed on the oil pick up tube..(where it bolts to the block). Installed it and took care of the problem.....only thing is you have to pull the motor to get to it...

 

Thanks for that. I believe it was a problem caused by the "mechanic" at our shop.
The motor shortly after it got running, wound up having a rod bend and knock off a piece of the piston sleeve.
Now we're on the 3rd motor. This time we didn't have any oil pressure. Had to send the whole van to the builder and have them look at it.
Thanks agian for the reply.

Robert P.