I am having a problem with my chevy silverado z71. It is a 2011 with 170000 miles automatically transmission. I started have losing oil pressure for a while. It will start out at a 35 40 pressure then drops after 40 mins to 25 30. I did an oil treatment to get and got the oil pressure switch changed. Please help.
What kind of "oil treatment?" Most oil additives are snake oil that don't do any good.
Is that oil pressure at idle? It is normal for oil pressure to go down when the engine reaches operating temperature. Did you check the specified oil pressure for that engine to see if you're out of specification?
Even with a new sending unit your dash gauge may be off. Verify oil pressure with a mechanical gauge.
If yours is the 5.3 then there's a couple of things you can check.
Under your oil pressure sensor there's a screen so make sure the guy who replaced the oil pressure sensor also replaced that screen.
And there's the O'Ring on the oil pump pickup tube. It's the red O'Ring in this picture and if it fails the oil pump can't suck up the oil like it should.
You have to drop the oil pan to change it.
It will start out at a 35 40 pressure then drops after 40 mins to 25 30
GM AFM engines are notorious for oil pressure issues. What is your VIN or engine RPO?
https://www.mightyautoparts.com/ontheline/otl-0721-low-oil-pressure/
http://www.engineprofessional.com/TB/TB103117-2.pdf
