Not sure if I should be worried or not. The oil pressure sending unit on my truck crapped out a while back and for various reasons I didn't get around to replacing it until a couple of weeks ago (while I was changing the oil so I know its not low). Everything appears normal except in one situation. If I make a short drive when the truck is cold then shut it off the oil pressure will come up to around 40 then slowly drop back down all the way to zero if it idles for more than a few seconds upon restarting it. a tap on the accelerator will bring it back up to normal but it falls back down. Once it gets warmed up everything is fine.

I guess I should add it's a 2005 Silverado Z71 with the 5.3L with 158K miles.

 

That is a strange one... Have you had it checked for codes?

 

No codes, and now it has gotten to the point where pretty much anytime the RPM's drop below 1K it drops off and the warning chime comes on. Normal pressure is around 40 when driving but now its having a hard time getting that high.

 

I think I would be hooking up a known good gauge in place of the sender.....just to confirm if its the sender or not

 

One of the guys I work with (I work at a dealer) told me that the oil passage that feeds that sender can get plugged up sometimes causing the gauge to do exactly what you're saying. You'll panic thinking you have no oil pressure, but in reality it's just that oil isn't making it up to where your sender is to push on the diaphragm.

If it were me, I'd run some seafoam in the oil for a while and see if that helps. I wouldn't run it for more than 500 miles though without an oil change. In other words, add seafoam, drive for 500 miles like normal, then change the oil. As long as your engine isn't noisy like it's got no oil pressure, I'd drive it.