HD OIL?

I don't disagree with you, because your engines had oil coolers, but for someone whose engine(s) do not have oil coolers, the multi vis oils may not be adequate.
The Volvo sterndrives that specified multi vis oils had engine coolers also. The Merc engines that did not have them specified the Merc 25/40 or straight weights.
 
Of all the internet reading I have done. Car / Boat mechanics I have known. Never heard anyone say they experienced or knew anyone who suffered engine damage or had longevity issues because they used this or that 'name brand' motor oil. The exception being newer oils without zddp being used in engines without roller rockers (excessive cam lobe wear) and engines that weren't serviced regularly. Having said that, a little common sense goes a long way, using a straight weight 40W in Alaska would be engine suicide. Most boats don't see Alaska temps. Engine cooling and water temps are related. I doubt in 50 degree water, using straight 30W oil as opposed to 10W 30 or 40 would make any difference. At the end of the day people will use what makes them feel all warm and fuzzy. From a practical standpoint I use synthetic oil in my vehicles in the winter because they flow immediately upon start up. Put a can of 5 or 10W 30 motor oil in your freezer at home, get the same of a synthetic of your choice. Next day turn them both upside down and see which one flows. Seeing is believing.
 
Kevdon,

I have 8.1 Crusaders and have been using Shell Rotella Diesel oil without problems - the guy at the autoparts store was telling me I didn't need diesel oil and I can't remember why I started. I was questioning myself, so thanks for saying that you're using diesel oil too!
 
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