Jason the non-mechanic is dead wrong!
An 87 305 should carry at least 15 psi oil pressure at full temperature idling and 45 psi. above 1,500 RPM. with the factory recommended 5W-30 in the crankcase.
Got to go with Country and avalanche. 10PSI at idle and an additional 10PSI for every 1000 RPM is a normal rule of thumb.
Using a thicker oil to cure oil pressure issues is just plain ignorant. Thicker oil creates pressure because it resists flow. Low oil pressure with the factory recommended oil viscosity indicates a failing or failed oil pump (very very rare) or increased bearing tolerances, which are very likely. Thicker oil creates a false oil pressure reading...it may be generating 40PSI from the oil pump to push the thicker oil through the pump and oil galleys, it does not mean that the bearings are getting 40PSI. Thicker oil cannot solve clearance issues. Fixing the clearance issues fixes clearance issues.
Edit: Jason, people like you are who give "mechanics" a bad name, and why tv stations do investigative reporting on shoddy/dishonest mechanic work. You have NO clue what you are talking about. Additionally, it was YOU who said "if low switch to heavier oil". If you knew half of what you think you know, you'd have a clue how the oil system in a chevy small block works, and you'd know that the oil pressure tap used in that truck is immediately after the oil pump. Since I'm not full of crap, and actually know what I'm talking about, here is proof for you: http://www.chevytalk.org/fusionbb/showpo... If the gauge reads 10PSI, that is before it has lubricated ANY bearing in the motor.
If you had as much pressure all through the oiling system, you'd see it blowing out the rocker arms. It doesn't come out at 30PSI there. It loses pressure from all the clearances within the engine. You could pressure tap every galley in the motor and you'd see a drop in pressure at every single point. Even with no clearance you will see pressure drop due to fluid interface with the galley walls over a given run...this is true of any fluid like air or water, or oil. This is how you calculate fluid flow in a pipe. You start with a bare minimum (10PSI for a small block at 1000RPMs) because it is known how much is needed at the far end of the oiling system, and at 10PSI to start, will have enough at the far end of the oiling system to keep things lubricated.
And you are darn right I'd run 5W-30 in a motor spec'd for it, you'd be an idiot not to. The manufacturer who spent millions in R&D, who designed, sold, and had to warranty their vehicle knows just a bit more about it than some guy in greasy coveralls. If pressure is low with the proper oil, you have internal engine problems that you don't fix with a can.
And yes, higher viscosity requires more energy to move (duh, why do you think 0w-20 exists?) so not only is the distributor shaft/oil pump having to work harder to push the oil in the first place, the oil is resisting flow all the way through the motor. You really think molasses requires just as much force to push through a tube as water given the same tube diameter? If one fluid takes more energy to move than another (the thicker one), it will have less energy at the other end if you start out with the same pressure.
20-30 idle 60-90 cruising. If low switch to heavier oil
minimum 10 pounds for every 1000 rpm
hi. i have an 87 chevy r10 305 v8. just curious where my oil pressure should be at idle and highway speeds. thanks for any help!
