Light-duty cruising- - - -virtually forever. If you work it hard, maybe 30,000 miles between overhauls. I mean long periods of high-RPM full throttle running like in a fully-loaded 2-ton or a dump truck, etc. Most of us don't use 'em like that anymore.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!