For those of you who subscribe to Classic Boating, there is a good article in the July/August issue entitled How Engines Work part II. Part of the article discusses oils. The "W" stands for winter which means it will hold it's viscosity at 0 degrees F. Otherwise the oil will hold it's viscosity at 210 degrees F. The higher the rating ie. 30,40,50 is for high compression engines. The oil temp for marine engines can go up to 240-250F which is why multigrade viscosity is advised. synthetic oils contain only 1 or 2 compounds and are derived from the liquefaction of natural gas. Synthetic oils will not breakdown as conventional oil does because of the temperature.
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