Originally Posted By: monster1
I think off the top of my head the manual says oil change every 100 hours. I've read from top marine mechanics say every 50 due to fuel delution. I'm right at 50 hours. I figure I spend the majority of run time at 3500 rpm doing about 32mph. So figure I traveled 1500 miles conservatively.
In second gear, going uphill, towing a boat, with flat tires.
FD is one. These engines also shear oil like Edward Scissorhands. They make a lot of metal too. Expect 50-80ppm iron for that 50 hour run.
FD is mostly a concern for trollers and people with a lot of no wake zones. Imagine starting your car and leaving it idling for hours.
100 hours is fine with a stout synthetic lube. If you have no oil cooler, your oil is getting hotter than stolen car with the heat stuck on in Arizona in July. If VP ever built a 4.3 with an oil cooler, I've not seen it.
FD can be funny though. When my old 454 had the garbage Weber carb that ran so fat under any adjustment that it turned my plugs black, and I had to cross an hour of manatee zones to hit the ocean, and only breathers with no PCV, I never turned up even a full percent of FD. Weird.
Using RT6 to 108 hours on that engine, I beat the iron universal average for 48 hours use, and still had about 7 TBN.
We've done even better using high HTHS 20w50 and SAE60 synthetics on these GM based engines.