"1. I have a 1979 Merc 470. Th
"1. I have a 1979 Merc 470. The orig owner's book says use 30 wt HD. When that designation first came into use I understood it to refer to High Detergent, ie oil that keeps dirt in suspension so the filter would remove it. I can verify that is does that, having torn down many pre-HD motors and a couple of Post-HD ones. The old motor pans had dirt caked in them. Also some folks said that HD meant Heavy Duty. Can't argue with that assumption. Anyway I have always stayed with the 30 HD.
2. My buddy, a Merc Tech Rep, says Merc oil has an additive that keeps the oil from draining off of the parts, thereby aiding greatly in a cold start. He also claims Merc filters are designed for the increased oil flow from steady 3/4 max rpm of boats, vs cars. Sounds reasonable. Anyone care to comment on these claims?
3. What is "dino" oil? Natural as in dinosaur vs syn?"