I am a 501 owner.* Some say that you need to run the 6v92ta's hard.* I dont.* I have been running my boat for years at 1100-1200 (8-9 knts)*Gets just over 1 MPG*at 1200 RPM (not good for a trawler but not to bad for a 60k lbs motoryacht. The only thing you must remember is not to let them run at idle speeds too long.*And change the oil more frequently if you dont run harder.* *Look at all the sportfish that run 600rpm for 8-10 hours a day.* The nice thing about the 501 over a trawler is if you need to kick it in the a** you can.* She cruises nicely at 2100 Rpm at 18knts.* But the Diesel will flow at that speed.
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I'd be interested to see an oil sample on that engine. As a diesel mechanic I was taught that a diesel should be run in the RPM range that it was built for. I know that the Detroits are pretty bullet proof, but a diesel is designed for thermal efficiency just as much as it is for volumetric efficiency. If it doesn't get to the right temperature range it doesn't combust the way it should. Running at lower RPM's can cause premature wear to the rings and sleeves. The most damage to these parts is done at start up because the engine is cold, as is the oil. If the engine is continued to run at lower temperatures this can cause early wear. I have limited experience with the Detroits but all Diesels are fundamentally designed and built the same. I also have seen a lot more engines from fishing boats being rebuilt then from other types of boats. Typically around the 8-12K hour mark, where as engines that are run in their designed RPM range have many more hours on them and still have great compression and glitter free oil. Maybe the Detroits are built so well that they can handle it. Any info from a Detroit expert would be appreciated because you are never too old to learn.