Originally Posted By: djb
The level drop depends on the engine, but it is often minimal. Oil systems have check valves all over that keeps the oil from draining back into the pan when the engine is off. On an engine I recently rebuilt the initial fill was a bit more than a quart extra over an oil change.
If your check valves leak you might actually be running a quart low.
Check valves "all over the engine" ... probably only one, located at the oil filter (ADBV). That has nothing to do with the oil level in the sump with the engine running.
The oil level in the sump will be the lowest at high RPM of course because the pump is flowing the most. Most high performance car makers say to add 1 qt to the engine for track use, which helps keep the sump level up during high RPM and cornering.
This isn't directly related, but somewhat. My motorcycle has a glass oil level sight window in the crankcase. The bike holds just under 3 qts of oil. When the bike is fully hot and running at an idle (~1000 RPM) the oil level goes down by ~0.4 qt in the sight window. If I rev the engine pretty good, the level will drop even a bit more, then take a few seconds longer to come back to the idle level after going back to an idle. When the oil is colder, it takes longer for the oil to drain back down for the level to stabilize. So doing high revs on an engine with cold oil will lower the sump level more so than if doing the same revs with fully hot oil. The hotter/thinner the oil, the faster it's going to drain back to the sump.