Did anyone catch this in the original post?
Quote:
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If it makes you feel safer, run a bit thicker oil but with thicker oil, comes increased engine wear at cooler temperatures and increased heat into the oil through more friction and less flow (flow and pressure are inverse, as you increase pressure, you decrease flow)
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VerusEric's post is very good on all points but he may want to edit that comment as not to confuse. That statement in bold does not necessarily apply to hydraulic systems with positive displacement pumps.
Our positive displacement oil pumps are essentially
constant flow machines. Increasing viscosity of a fluid in a fixed system with a positive displacement pump, increases system resistance (pressure) but does not decrease flow unless there is unanticipated system leakage or in the case of our engines (and most), a pressure relief valve.
Assuming the oiling system is operating at pressures below the point that fluid escapes past the PRV, then a change in viscosity will change pressure but not flow.
With multi-viscosity oils you can also run a thicker oil without sacrificing startup wear. In short, a 0w-40 should produce the same protection at startup as a 0w-20 (because 0W) but at operating temp it will produce more pressure (because 40)
and if the PRV
isn't part of the equation, the flow will be more or less the same.