AMSOIL FORMULA 4-STROKE® MARINE SYNTHETIC MOTOR OIL (WCT) SAE 10W-30 has a HTST of 3.64 (can't link due to board rules).
Still waiting to see all these dead engines due to the use of 20 grade oils...
Additives do most of the protecting IMHO. Gary ran Bruce's 10 grade stuff and came out just fine.
The 50 grade probably won't kill your engine but there is no need for it. Buy some 10W30 PP and be happy.
