Help! I have a 2003 GMC 6 liter that suddenly lost all oil pressure. I have removed the sending unit and manually tested oil pressure and found none. Oil pickup tube was still attached and o-ring seal "looked" good. Oil pump was disassembled and "looked" ok. Any suggestions? Relief valve was clean in oil pump(no trash). This truck has apprx 150,000 miles and had excellent oil pressure until this happened.

 

Check the oil pan gasket. I had an avalanche that blew out the pan gasket and lost oil pressure. It leaked back into the crankcase.

 

I've had several here in the shop that just had the oil pumps go bad. One customer was letting his truck idle and about 10 minutes later he came back out and the truck was knocking and thrashing and he saw the oil pressure was at less than 5lbs. When we got the truck hauled in here, the oil pump was just simply....dead. Don't know why or what made it go bad. Oil looked good and everything looked fine. Sometimes you just get a pump that will *** out on you.

 

I've rebuilt two engines that used Fram filters . . . When the motors were torn appart, I found filter material in the cam bearins and main bearings. Both engines ran, but showed really low pressure.

Low pressure after a cam swap - I've done a cam swap in a 5.3 and tried to reuse the oil pump oring - the blue o-ring does not re seal correctly . . . replaced it with the newer style and had not issues.

The cam bearing motor - spun the bearing right out of the block, and fused itself to the cam. I had to cut the bearing off with a dremel to get the cam out of the block. It had about 10lbs of pressure and still ran.

The motor with the bad mains would run for 1-2 min, then it would have a really nice vibration - it was as if you were dragging a metal file cabinet across the floor.

 

The check valves in the oil pumps in these engines are known to freeze from time to time. I've seen it on a few occasions through our shop.

 

Hey Guys, Thanks for the suggestions. Am going to install new oil pump and pickup tube o-rings and see if the pump may have just lost prime. Might not need the new pump but for the $100-$150 it cost I don't want to trust the old one.

 

Hey guys, I had new oil pump and o-rings installed today. Just put oil pan and front cover on and fired up for a few moments. Long enough to find we DID have oil pressure now. Shut it off reinstalled all the other stuff and fired it up again. After about fifteen long seconds all of the valve noise stopped and she runs out good. Thanks for the help. Either just a bad pump or one that lost it's prime somehow. don

 

I'm always incredulous when I read these postings about the GenIII pump failing. What was the failure due to? Did the gears eat themselves up? I doubt it. Did the "O" ring cause cavitation? Maybe. Was the pickup screen clogged with debris? Possibly. I'd like to see the gears inside these "failed" pumps put up for viewing. Did these pumps "fail" after having been removed and then reinstalled during engine modification? GM has a complex procedure for insuring that the pump and gears are concentric to the crankshaft when it is install. Were these pumps installed without being checked for concentricity? Could be, but I doubt it. I just don't buy it. I'm not convinced.

 

You probably won't garner many responses to your post because most people don't even know what "concentricity" or "cavatation" means.

 

I've seen 4 of these fail at the dealer with no mods done. I thing the regulator valce sticks in the bore. Who knows. Once I take it off, inspect it and check the pick up screen. I'm not going to put the old one back on to see.