Small 90s econobox, 4 cylinder. ~300k miles. Stickshift, so engine speed is always proportional to road speed at relevant freeway speeds.
Crossing the country recently, I observed extremely high oil consumption and leakage all over the engine. This was later traced to a valve cover gasket that hardened (ceased to be rubber-like). That was replaced. There is now no evidence of external leaks.
However, crossing the country back, I discovered the engine still had very high oil consumption - 1 quart every ~400 miles. Clearly an internal leak. No discernable "blue smoke". However, this only occurred in the states that allowed 75-80 mph cruising. In the states which allowed 65-70 mph cruising, oil consumption was much, much lower - ~1 qt per 1000+ miles.
So clearly, engine RPM has everything to do with it. Altitude does not; it did the same in eastern Nebraska (1000-2000') as Wyoming (5000-7000').
A possible factor is the engine being about 1 quart low on coolant for about 1000 miles. Added water was gulped up by the engine, so clearly the top of the cylinder head suffered uncovery; however, the coolant temp sensor in the head read normal values at all times (there's a coolant gauge and it works). Perhaps this accounts for the valve cover gasket losing its suppleness, and perhaps the new oil leak???
(despite the misadventure, the cooling system is tight as a drum. No leaks, proper overflow tank behavior.)
Which source of oil leak would be indicated by "only occurring at high speed" and "possibly being caused by overheat from low coolant"?