SOURCE: low oil when engine warms up gmc sierra 1995
30-40 psi of oil pressure is fine for many vehicles including your GMC. I am assuming that the truck has more than 100,000 miles on it and still has the original engine in it. By rule of thumb you only need 10 psi per 1000 rpms in a typical street driven engine to give adequate oil pressure to keep the bearings from oil starvation. The oil pressure is typically higher when initial start up occurs because it is more viscous due to the temperature of the oil as the engines oil warms up the visconsity thins out and the oil flows more smoothly. The drop in oil pressure is a normal occurance. Above 45 is more than required for a daily driven street engine. I believe that the specs on that engine only list 30- 45 psi.
SOURCE: 1993 GMC Sierra C1500 5.7 just recently started
Most likely the Gage is not the problem these rarely go out. If the pressure is only dropping then the oil pump is getting weaker or is filling with sludge. Try running the engine with an oil additive such as marvel mystery oil or sea-foam. Then after the additive has circulated through the engine for a few heat ups and cool downs you can change your oil. the pressure should change almost immediately. If it doesn't then check the oil pressure switch. You can look on the side of the block and there will be a small piece shaped like a pencil with a wire coming from it. This piece is the oil pressure switch. Hope this helps. Please rate me if you think this helped. Good luck.
SOURCE: LOW OIL PRESSURE ON 2007 GMC SIERRA 1500. CHANGED
have it tested using a manual gage if still low then main baring ore most likely bad that would mean a over hall if is really low and bearings bad should be making rattle noise when started up first few seconds
Testimonial: "thanks alot.truck is not making a rattling noise.we did check it with a manual gauge.it read about 10 at idol. press. gets better as you incr speed"
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