I have an 06 Z71 with 5.3 engine and 195,000 miles on it. My oil gauge is normally around 40. Yesterday I noticed it went up to 60. Today it started getting close to 80 (max on gauge). When I stopped it would drop back to 60. It then went to 80 and stayed there. I stopped and shut engine off. I checked the oil level it was on the full mark. I continued driving home and shut it off. As I opened the oil fill cap it sounded like pressure relieving. There was no oil on backside of oil cap, the dipstick was still in place. I would think if the pressure was really getting very high that the dipstick would have popped up some and or oil would have been on the backside of oil cap. My check engine light is on already for a knock sensor, I was going to buy a code scanner and see if there are any other codes. I'm looking for ideas of what to check.

 

It could be the oil pressure sending unit or the gauge. You could do a google search on testing the sending unit. The unit is behind the intake on the drivers side.

 

I googled it like you said. I'm going to check it this weekend. I have parked it until I get this fixed. I will post the results.

 

I'd remove the sender and hook up a mechanical gauge and see what that reads.
Highly doubt you were building crank case pressure as it would require blocking off the fresh air inlet and would have most likely pushed the dipstick up so it could vent.

Also I think your in the age range of the bad GM clusters.

 

My '05 Z71 did pretty much the same thing, most likely is the oil pressure sending unit. The easiest check (IIRC) is to turn the truck on, but not start it. If it goes straight to 80 the sending unit is bad. I've been driving around with it like that for almost 2 years and no problems.

 

I haven't had time to work on it yet. I'm going to try and check it out this weekend.

 

Today I replaced the oil pressure switch and that fixed the problem. It was $40 at Autozone and $10 for socket for oil pressure switch. Now the gauge reads around 40 again it's working fine.

 

Glad to hear you found the solution.
Great end to a helpful thread