Im looking at a 20 HP Suzuki 4 stroke outboard. I fish year round including the winter. I always have some 5w40 diesel oil around and was wondering if it would be ok to run in the outboard? It calls for 10w40, and 10w30 in the winter. I'm thinking 5w40 would be ok year round? Especially since I already have that on hand for my trucks, bike and ATV; it would be convenient and cheaper than 45 dollars a gallon for Suzuki oil.