Just like your car, boats need to have their oil changed. Four-stroke outboards, inboards and stern drive boats require regular oil changes. The frequency will vary by model, but a good rule of thumb is to change the oil every 100 hours of operation or at least once a year. Check your owner’s manual the correct grade of oil. Marine oils are different! They include more corrosion preventers that standard 4 stroke oil and should meet stringent NMMA FC-W anti-rust testing. Do you use you boat a lot? Try Amsoil 4 stroke marine oils & filters to extend your oil change interval and you might even get a fuel economy boost. AMSOIL Formula 4-Stroke® Marine Synthetic Motor Oil is a premium-quality synthetic formulation engineered for the harsh operating conditions of marine environments. It withstands the intense mechanical action of continuous, high-rpm operation to deliver superior viscosity protection. Formula 4-Stroke Marine Synthetic Motor Oil is specially fortified with a heavy treatment of advanced additives that protect motors against wear, rust and deposits. It excels in high-horsepower applications and all-day trolling conditions. For more information on Amsoil products visit: http://www.amsoil.com/shop/by-product/?i=1&zo=1433133