Quote:
Originally Posted by Old Mechanic
Years ago (maybe 25) Ford dropped the spring pressure on their relief valves, so max oil pressure was reduced by almost 50%. That alone netted them an estimated .5 MPG on the EPA cycle. They also found that modern oils work just as well or better using the philosophy of higher flow versus viscosity as had been done decades ago. The variable displacement pumps are another step in reducing oil pump drive losses.
I would just run the lowest viscosity oil recommended for your engine, but beware of manufacturer specific limitations. I know Nissan still recommends 5w-30 weight due to cam lobe wear issues, where they have finer surface finishes that need that viscosity.
regards
mech
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I have to admit that I haven't followed the oil pressure specs of many different types of engines over the past few decades, but I have noticed a few trends in some vehicles. In the high performance small block chev builds from the 70s/80s virtually everyone would go for a high volume oil pump (Mellings high volume pump was extremely popular), the theory being that it would help with long engine life when forcing the engine to tolerate loads that the om never intended, but this thinking changed somewhere along the way, and now the pro's (David Vizard for one) use the standard volume pump for the purpose of saving a few horsepower. The small block chev has a well designed oiling system, so more volume apparently isn't needed, as the original pump is already bypassing oil at reasonably low revs. (2500ish from memory).
The most often quoted hot oil pressure in small block chev performance builds is usually around 60-70 psi. Ford's Cleveland engine doesn't have a particularly good system, and there was talk of owners using 160 psi of oil pressure (along with oil gallery restrictors to keep more pressure in the crank with less going up to the top end of the engine) in high performance apps. to help the bearings survive.
Obviously the intended use of the engine has a bearing (no pun intended) on "safe" oil pressure in the older engines, so running a lower pressure in an engine can theoretically work if engine loads are kept on the low side.