I have a 2011 GMC 2500 with the 6.0 roughly 130-140K on it. I changed the oil in April and just before I did I noticed that instead of being at the usual 40 PSI at idle it would fluctuate down to 20-30 PSI and when you accelerate it would come right back ( to me a sign of just really over due for an oil change). After the oil change it went right back to normal 40 PSI at idle. I went to start it up couple of weeks ago I took the truck in the morning and it was fine came home parked it. In the afternoon I went to move it out of the way and noticed the oil pressure never came up at all. I let the truck idle down the drive way and shut it off and ordered an oil pressure sensor, put the new one in and no difference. when I was trying to determine if I needed the screen or not I took a picture and zoomed in to see if there was a screen in there or not and it appears that the bottom of the port is dry and rusty and doesn't look as if it has seen oil in quite some time. I started the truck with the sensor out and let it run for a few seconds and nothing no oil came out of the port and when I took the pressure sensor out bottom of it was clean as shiny the the same as if I had just taken it out of the package.
Last night I went back to the last thing I touched, the oil change. thinking maybe the Fram filter was blocked by something, I put a wix on, started the truck let it run until the low oil message came on then shut it down. As expected the oil filter was full, so I cracked the filter and put a drain pan under it and restarted the truck and instantly you could hear the oil spraying out around the filter. I crawled under the truck and had oil on the diff, the side of the pan, the axle everywhere so it was coming out with some volume. When I measured what had come out and collected in the pan it was over a quart maybe a quart and a half, in under 10-20 seconds.
From that I am assuming that the pump is working, the pick up tube is working, could be bad o ring on pick up tube, (being 4wd I really don't want to drop everything to get to the oil pan to replace an o ring that may not even be the issue.
At the point the motor sounds the same no rattling, tapping, etc.
Any suggestions of what else to check before bringing it to a garage? I have limited tools and am doing this in my front lawn as I don't want to drive it at this point.
