Re: Boat Oil
Like Rick tried to point out, marine engines should be using FC-W certified oil.
Take a moment, and read as to why:
Until FC-W, engine manufacturers have specified the use of a high-grade automotive engine oil for four-stroke outboards. But in recent years automotive oil formulas have changed, as car and truck manufacturers put more emphasis on reducing internal friction to improve fuel mileage. This made auto-spec oil less desirable for use in marine engines, where operating conditions are significantly more challenging. For example, how often and for how long do you run your car or truck at full throttle? Maybe for a few seconds as you accelerate down an on-ramp. Your outboard, on the other hand, may spend a lot of time at WOT. Even when cruising, an outboard is under relatively heavy load and at least 75 percent throttle while it operates in an environment that includes high humidity and salt air. Compared to a car engine, an outboard leads a tortured life.
In designing the FC-W formula, the NMMA committee sought to address two key issues. The first is resistance to "shearing" during high-rpm and high-temperature operation that rarely occurs in an automotive application. Under shear stress, oil can become thinner and lose its ability to separate moving parts, leading to accelerated wear or even catastrophic failure in extreme cases. The FC-W spec imposes a higher minimum viscosity level, which means that FC-W oil will not thin out as much as automotive oil of the same viscosity under the same heat and rpm conditions.
The second issue addressed by the FC-W standard is corrosion. Obviously, an outboard lives in an very humid environment that can also be salty. When the engine is shut down, air remaining inside the engine can condense on bare-metal surfaces and this moisture can either attack the metal directly or become mixed with the oil and circulate through the engine. The FC-W spec adds a rust-inhibitor requirement that does not exist for any automotive engine oil and will better-protect vulnerable surfaces like valve springs and cylinder liners.
FC-W oil is mother's milk for four-stroke outboards, but it is also recommended for use in four-stroke personal watercraft and gasoline inboards and sterndrives. Of course, because this is premium oil, it has a premium price. A one-liter bottle of Mercury 10W-30 FC-W oil is $3.30, while a quart of Yamalube 4-M is $4.99 at my local dealer. That's more than store-brand auto oil, but about the same as a quality synthetic motor oil like Mobil 1. Pennzoil and other oil companies also offer oil that meets the FC-W standard.
