In researching information I've gathered some interesting info regarding motor oil. From the info I gathered, this is what I'm getting from it.
Pressure is an opposition to flow
Thicker oil resists flow more than a thinner oil (easier to push a thinner oil than a thicker one)
Better oil FLOW = better lubrication = better cooling
Oil pumps DO NOT create pressure, they create oil FLOW. The resistance to flow that the thickness of the oil + the size of the passages provides creates the pressure. The bypass spring governs how high this pressure can increase.
An increase in flow will cause an increase in pressure. Pressure will only increase to the point at which the pump bypass allows it to. Oil pressure can only be increased by an increase in flow. Once pressure rises enough to open the bypass, oil flow through the engine will no longer increase with RPM. The pump will still pump more oil volume with an RPM increase, however the increased flow of the pump is bypassing instead of providing an increase in flow through the engine, indicated by the pressure holding steady as the RPMs increase. Having said that, it would make sense to run the thinnest oil possible that will hit the bypass at your max RPM yet still maintain a minimum of 10 PSI per 1,000 RPM.
Running too thick of an oil will cause it to overheat at max RPM. This would be indicated by pressure dropping at max RPM. The pressure drop is indicating that the oil is reaching a temperature at which it flows better, however this temperature is so hot that it overheats the oil and it simply cannot cool or lubricae the parts. By running a thinner oil, the oil can flow better at a lower temperature than a thicker oil can, and therefore increase cooling at a lower temperature. Due to the lower temperature, the oil will not lose its viscosity like the thicker oil did.
Engines with looser clearances will benefit from running a thinner oil. With the increased amount of space between the parts, thinner oil can fill those spaces quicker than a thicker oil can due to the fact that it flows better than the thicker oil at a lower temperature.
Pressure should increase with RPM, indicating that flow is also increasing with RPM (increase in flow causes increase in pressure). If pressure is NOT increasing with RPM, this means that flow is not increasing with RPM since an increase in flow causes an increase in pressure.
Example - You have an engine with an oil pump that bypasses at 50 PSI. An oil pump at 1,000 RPM idle is spinning at 500 RPM. At 500 RPM, it can only push enough oil through the engine to lubricate it at an idle.
Let's say that by 1500 RPM, you're already hitting the bypass. This means that the oil pump will bypass all additional oil flow past this RPM and it will only flow enough oil through the engine to lubricate the engine at 1500 RPM because it is bypassing the rest of it. Flow can no longer increase with RPM at this point, which causes the pressure to hold constant. Since you're only flowing enough oil to lubricate the engine at 1500 RPM, any increase in engine speed will overheat the oil, causing it to thin out, which will cause it to flow better, but the oil is so hot that it cannot properly lubricate and cool at this point.
Example 2 - You have an engine with the thinnest oil that will provide a minimum of 10 PSI per 1,000 RPM. You idle at say...15 PSI. The pump will not bypass until 60 PSI. With this setup, flow will increase with RPM because the bypass is far from being open, so the oil has no choice but to flow through the engine. As flow increases, pressure will increase as well until it hits the bypass. In an ideal situation, this would not happen until the engine reaches max RPM.
Pressure that increases with RPM indicates an increase in flow. High pressure readings that hold steady as RPMs increase indicate that you're running too thick an oil for it to flow properly.
The idea behind oil pressure is to run the thinnest oil that will provide a minimum of 10PSI of pressure at 1,000 RPM, yet will not pop the bypass open until at or just before you hit max RPM. Pressure at the bypass opening point should be a minimum of 10 PSI per 1,000 RPM (at 6,000 RPM, it should be no lower than 60 PSI).
The thickness of the oil is NOT what provides the "cushion" between parts. Oil PRESSURE is what does this.
Am I wrong in thinking this?