Is it OK to Use Automotive Engine Oil in a Marine Engine?
Automotive oil definitely does not belong in the sump of your marine engine – outboard, sterndrive or inboard. Here’s why.
The inner workings of your boat engine might look like those of an automotive engine, but your boat engine operates in a much different environment. In fact, it’s one of harshest environments imaginable for an engine. With each piston stroke a marine engine draws in very humid air directly off the water’s surface. When the engine is not in use – often for weeks at a time – this humid air can enter combustion chambers through open valves, where it can condense on bare-metal surfaces and cause corrosion on components such as valve springs. In a saltwater environment, that air is even more corrosive.
A marine engine is also a real torture chamber for oil. How often do you drive your car or truck wide open, with the pedal pressed to the floor? Maybe for a few seconds as you accelerate onto a freeway or pull out to pass? An auto engine spends most of its time just loafing along. But a marine engine is designed to operate for hours at high rpm and under heavy load. This extended high-rpm operation can literally shear (or split) additive molecules in ordinary automotive oil, reducing lubricity. Under shear stress, oil becomes thinner, permanently losing viscosity and its ability to separate moving parts. This leads to greater wear or even catastrophic failure in extreme cases.
The FC-W® Standard
Always consult your owner’s manual for the exact oil type and viscosity specification recommended for your engine. Most manufacturers will require oil that carries an FC-W® certification, a minimum standard devised by the National Marine Manufacturers Association® (NMMA®) for marine engines. Oil that is certified to meet this standard will have the FC-W symbol on the label. A container with the FC-W (CAT) symbol signifies a marine oil designed to be compatible with four-stroke marine engines that have an exhaust catalyst.
Compared to regular motor oil, FC-W oil features:
- More corrosion inhibitors to deal with the marine environment, long periods of inactivity and long periods of operation at low speeds during which the engine is below its ideal operating temperature.
- Greater resistance to shearing – that permanent loss of viscosity that occurs when larger oil molecules are cleaved by mechanical forces.
A marine engine operates at a much lower temperature than an automotive engine, especially during periods of extended idle, such as trolling or navigating long no-wake zones. This is by design, because if the temperature of saltwater rises above 170 F it will begin to crystallize in the engine coolant passages. Marine oil contains specific additives that help to provide adequate lubricity at these lower temperatures and resist the effects of fuel contamination, which can occur during long periods at idle when unburned fuel condenses on cylinder walls.
The line of premium Quicksilver Marine Lubricants products includes FC-W and FC-W (CAT) certified Quicksilver 4-Stroke Marine Engine Oil for any marine engine brand, specifically formulated for the unique needs of the marine environment. Note that FC-W is a minimum standard. Top-quality oils such as Quicksilver products exceed those minimum standards and are tested and proven to provide industry-leading protection against rust and corrosion, to offer increased wear protection and to have optimal viscosity retention. Your marine engine deserves the good stuff – Quicksilver 4-Stroke Marine Engine Oil.
Always dispose of waste oil properly. Go to Quicksilver Where To Buy for retailer information.