How to Choose Your Outboard Motor Oil: Other Factors
In addition to viscosity, flash point and pour point, there are a few other specifications that will help you decide whether Evinrude XD100, Yamalube or some other oil is right for you. When oil reacts with sulfuric acid and burned, there is always some amount of solid residue. The amount of this solid material that is leftover is referred to as the percentage of sulfated ash.
In oils, zinc is used to prevent damage that would be incurred when two metal parts come in contact with one another. The amount of zinc that is used is reported as the percentage of zinc, which is typically about 0.1%. While these specs will give you a good idea of how the oil will perform, you should also consider the base stock and additives that the manufacturer uses in production.