1993GMCSierra
I'm Awesome
5W-30 has been what GM has recommend since the 1980's, and it does a fine job of lubricating these engines if they are in good shape. Mine has run Mobil 1 5W-30 since it was picked up at the dealership, and 132,000 miles later I still have 40 PSI at hot idle, and 60-70 going down the road.
It's all about the shape of the engine. If your engine is putting out low oil pressure with the recommended oil, it's a sign the engine is just worn. All the oil pumps do is pump the oil, it's the internal clearances in the engine that give it the pressure. As the motor wears out (lack of oil, conventional oil, too thick/thin of oil, and just use/abuse) those small clearances get larger, resulting in a drop of oil pressure.
Think of the oil pump as a garden hose. Turn the hose on, and it pumps out water, same speed, same flow rate. Stick your thumb over the end, and you have less water coming out, but at a higher pressure. That's what the small holes in the bearings do. They only shoot out a small amount of the oil that is provided to them, but at a higher pressure. As they wear out/down, the pressure drops.
On my old GMC, the head gasket blew 2 miles from home, and was dumping coolant into cylinder #5, and the oil pan. I wasn't going to just park it there (no one within 30 miles of here has a tow truck), so I drove it home, shaking and all.
Well, my oil looked like chocolate milk when I parked it. After I replaced the gaskets and all, I had next to 0 O/P at hot idle, and only about 25 psi going down the road at 60 MPH, where before I was around 25/45. Me driving it home those two miles contaminated the oil to the point I had metal on metal contact with probably every mated surface in the engine. This seriously accelerated the wear in the engine to the point that by the time the oil got to the sending unit, there was no pressure under 1,100 RPM's or so.
I sold the truck about a year later, the only way I got it to have about 15 PSI at idle is with 3 quarts of 10W-40, and 2 quarts of Lucas Oil Stabilizer. Whereas before, 5W-30 was just fine.
It's all about the shape of the engine. If your engine is putting out low oil pressure with the recommended oil, it's a sign the engine is just worn. All the oil pumps do is pump the oil, it's the internal clearances in the engine that give it the pressure. As the motor wears out (lack of oil, conventional oil, too thick/thin of oil, and just use/abuse) those small clearances get larger, resulting in a drop of oil pressure.
Think of the oil pump as a garden hose. Turn the hose on, and it pumps out water, same speed, same flow rate. Stick your thumb over the end, and you have less water coming out, but at a higher pressure. That's what the small holes in the bearings do. They only shoot out a small amount of the oil that is provided to them, but at a higher pressure. As they wear out/down, the pressure drops.
On my old GMC, the head gasket blew 2 miles from home, and was dumping coolant into cylinder #5, and the oil pan. I wasn't going to just park it there (no one within 30 miles of here has a tow truck), so I drove it home, shaking and all.
Well, my oil looked like chocolate milk when I parked it. After I replaced the gaskets and all, I had next to 0 O/P at hot idle, and only about 25 psi going down the road at 60 MPH, where before I was around 25/45. Me driving it home those two miles contaminated the oil to the point I had metal on metal contact with probably every mated surface in the engine. This seriously accelerated the wear in the engine to the point that by the time the oil got to the sending unit, there was no pressure under 1,100 RPM's or so.
I sold the truck about a year later, the only way I got it to have about 15 PSI at idle is with 3 quarts of 10W-40, and 2 quarts of Lucas Oil Stabilizer. Whereas before, 5W-30 was just fine.
