Difference in Oils

I often get asked if there is really a difference between outboard 4stroke oil as opposed to the oil we put in our cars. My answer is most definitely and if you want to get the longest life out of your engine you should only use an oil that is FC-W rated and here’s why. The major differences between API and FC-W oils are higher levels of ZDDP, viscosity, rust preventative agents, and anti foaming standards in FC-W oil. API oil or oil rated SM has lower levels of a substance called ZDDP, an anti wear agent. In 2005 the EPA decided that ZDDP and catalytic converters did not get along and mandated that the levels of ZDDP be lowered in API oils. The National Marine Manufacturers Association, NMMA, recognized the significance of this and developed the FC-W standard for 4-stroke oil as an outboard runs at higher RPMs and loads than an automotive engine and has much higher requirements to meet. Another major factor is in the viscosity or at what thickness oil stays at during different heat ranges. One of the major factors in the FC-W rating is an oils high temperature high shear strength measurement or how much lubricity an oil has at 130 centigrade. API Oil can be as low as 2.9 while the minimum for FC-W oil is set at 3.3. API oils are formulated to give high gas mileage and the average 10W30 oil has a rating of 3.1 and does not make the cut for FC-W consideration. Another factor is the amount of rust prohibiting agents FC-W oil has over API oil. This is a huge difference, as outboards tend to sit between uses and have issues with condensation etc. that our cars don’t seem to have. Anti foaming is the amount of air oil is allowed to carry before it froths. Engines running at high RPMs are more likely to cause oil to develop and trap air in the oil. To this end FC-W oil is similar in requirements to racing oils.
Outboards will not immediately have problems if you use an API rated oil nor will you have a difference in performance. Long term durability should be increased by using FC-W oil.
Till next time “Keep it in deep water.”