Recently purchased a 2013 Silverado with a. 5.3 ltr. The oil presure dropped when im at an idle to 20 psi. Is this engine crap? I checked with the dealership and they said it meant minimums on the oil presure and I'm concerned that this isn't just a way to keep from doing warrenty work? Can anyone tell me what a normal 5.3 ltr engine should read for pressures?

 

minimum oil pressure as a general rule of thumb is 10psi per 1000rpm.

they did have issues with the oil pressure sensors and screens but they would cause the sensor to read below 4 psi. removing the sensor and replacing the blocked screen fixed the problem.
20psi will not set a warning. Did you actually put a pressure gauge on it or just read a data parameter with a scan tool?

 

Not a issue. My commercial trucks, while operating under load, have oil pressures at 45-50 psi, but as soon as they go to idle, they are down at 25-28 psi.

Pressure is related to both pump flow and viscosity. Viscosity is not the "weight" or "thickness" of an oil, but a measure of resistance to flow. A typical 5w30 will have a viscosity of around 55 cSt at room temperature, but only about 10 cSt at 212F. It flows easier when hot. Since part of oil pressure is a measure of resistance, or kinematic viscosity, hot oil will typically have lower oil pressure except when operating at road speed RPM's, where the pump is pushing so much oil thru that the pressure rises.