What is the oil pressure supposed to be on a chev 5.7 at idle?

Answer 1

If you're asking this question one must assume that your idle oil pressure is down so here's a brief explanation on oil pressure and what's going on inside the engine when the oil pressure light goes on:

The oil pump is in the bottom of the engine, and can only be accessed by pulling the oil pan. It's a gear pump, meaning that there are two gears that spin and mesh to force oil into the oil journals.

The oil pump is capable of creating A LOT of pressure and it's strong enough that if the oil pressure is forced above a specific point the torque that the pump would require is capable of destroying the shaft that drives the pump. With that in mind, the engineers have put a regulator inside the engine. It's a simple regulator, just a piston pushing against a spring. There is a dump port about halfway up the regulator shaft. When the piston passes the port oil is dumped back into the crankcase and the oil pressure never exceeds the setpoint pressure, typically somewhere around 40 to 60 PSI, depending on the engine.

Now forget all of that, because the only thing we're concerned with now is where the pressurized oil goes and what happens when the pressure drops.

Pressurized oil that makes it past the regulator travels through a series of "journals" to the bearings (crankshaft and camshaft) and hydraulic lifters. Not all engines use hydraulic lifters and the only thing that matters is that they exist and typically work quite well.

Pressurized oil is directed into the hollow part of the crankshaft main bearings where the oil pressure literally keeps the bearing from touching the crankshaft. The crankshaft also has oil journals that direct the pressurized oil to rod bearings.

When it's all working properly the bearing rides on a film of pressurized oil never touching the crankshaft and the bearing could technically last indefinitely. But the real world is a little less than perfect, when the engine is started "cold", there is no oil pressure and the bearings briefly touch down, causing just a little wear.

The distance between the bearing surface and the crankshaft in a new engine is quite small, just enough to allow a film of pressurized oil to build up. The pressurized oil slowly leaks past the bearing and the oil pump replaces the oil keeping the bearings pressurized.

As the main and/or rod bearings wear the gap between the bearing and the crankshaft becomes larger. The larger gap allows the oil to leak past at a much higher rate, but that's ok, your oil pump is capable of pumping quite a volume of oil and can usually keep up until the bearings become quite worn.

Back to the pressure regulator: you should notice that the needle on the oil pressure gauge seems to always stop at a certain point, it never goes any higher... that's when the pressure regulator is taking over. If the engine is not significantly worn the oil pressure gauge will always stop there.

When the engine is a little worn the bearing surfaces open up and the pump will not be able to maintain enough flow at an idle to run the pressure up to the regulator bypass pressure. It's just the normal life cycle of an engine and it doesn't mean the engine is worn out and should be replaced... yet.

Once you start noticing that the oil pressure drops when the engine is idling, you should start to investigate using a higher viscosity oil in the engine. Higher viscosity just means that the oil is "thicker". Viscosity of zero is basically the same as water. Most newer engines use 5W15 or even lighter, slightly older engines use 10-30 and a lot of worn engines go to 15W40 or even thicker.

Thicker oil leaks past the bearings SLOWER, allowing the oil pump to keep up with the demand, that way it can pump enough oil to keep the pressure up to the regulator bypass pressure.

Simple answer, the oil pressure SHOULD always be riding at the bypass pressure, whatever is normal for your engine.