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Formula 4-Stroke Synthetic 10W-40 Motor Oil

AMSOIL Formula 4-Stroke Synthetic 10W-40 Motor Oil


Four-stroke gasoline engines have long been a mainstay of the general marine industry. They have succeeded in reducing emissions and increasing fuel efficiency, and they have also been a hit with consumers. In fact, Mercury Marine has seen its four-stroke outboard sales surpass its two-stroke sales. When four-stroke outboard motors were introduced to the market, manufacturers recommended either their own specially formulated oil or an API SG or SL automotive oil. However, because the specific lubrication requirements of automobiles and outboard motors are different, it soon became apparent that four-stroke outboard motors would require their own oil specification. This standard, entitled FC-W, was released by the National Marine Manufacturers Association (NMMA) in August 2004.

New AMSOIL Formula 4-Stroke® Marine Synthetic Motor Oils are premium quality synthetic formulations engineered for the harsh operating conditions of marine environments. They withstand the intense mechanical activity of continuous, high RPM operation to deliver superior viscosity protection. Formula 4-Stroke® Marine Synthetic Motor Oils are specially fortified with a heavy treatment of advanced additives that protect motors against wear, rust and deposits, and they excel in both high horsepower applications and all-day trolling conditions (see four-ball wear chart).

4-Stroke Outboard Motor Warranty Certified

Formula 4-Stroke@ Marine Synthetic Motor Oils are certified by the National Marine Manufacturers Association (NMMA) for use in four-stroke outboard motors. These high quality oils demonstrate outstanding performance, exceeding the NMMA "FC-W" (Four Cycle - Water) specification requirements. Only seven manufacturers currently produce FC-W certified oil. Formula 4-Stroke® Marine Synthetic Motor Oils fulfill the warranty requirements of four-stroke outboard motor manufacturers.

  • NMMA Registration #FB-30010B 10W-40

Superior Protection Against Engine Wear

Marine engines operate under high loads and RPMs for extended periods of time, causing traditional automotive oils to break down and lose viscosity. While automobile engines normally operate at around 2,500 rpm, outboard motors can run twice as fast, requiring greater levels of wear protection and better bearing durability than automobiles. In addition, prolonged idling and low operating temperatures contribute to fuel dilution, further thinning the oil. To ensure adequate protection for their engines, marine engine manufacturers set minimum high temperature/high shear (HTHS) viscosity limits. AMSOIL Formula 4-Stroke® Marine Synthetic Motor Oils are shear stable and formulated with sophisticated oil additive chemistry, exceeding the HTHS requirements of both the API and NMMA FC-W (see graph).

Click on graph for larger image

Four-stroke engines in inboard and sterndrive power plants feature horizontally mounted crankshafts, retaining a small level of oil in the bottom of the crankshaft bearings upon shutdown. This residual oil helps protect the bearings until the oil pump can supply additional oil volume. However, the design configurations of four-stroke outboard motors present a challenge to marine lubricants. Four-stroke outboards feature vertically mounted crankshafts, limiting oil retention at shutdown and increasing the likelihood of dry starts and accelerated wear. Formula 4-Stroke® Marine Synthetic Motor Oils contain a high concentration of premium quality anti-wear additives that provide an extra level of wear control upon start-up.

Excellent Anti-Rust Performance

Marine engines are prone to rust, leading to uncontrolled wear and premature engine failure. However, good rust protection is not a natural attribute of engine oil. It comes only by design. Formula 4-Stroke® Marine Synthetic Motor Oils contain maximum treatments of special rust and corrosion inhibitors that ensure long-lasting engine protection during both idle and storage periods.


AMSOIL Formula 4-Stroke® Marine Synthetic 10W-40 (WCF) Motor Oil is FC-W registered and warranty certified for use in four-stroke outboard motors. It surpasses the FC-W four-stroke outboard motor performance requirements established by the National Marine Manufacturers Association (NMMA) and are recommended for gasoline-fueled four-stroke outboard, inboard, stern drives (inboard/outboards) and personal watercraft motors. Use the appropriate viscosity grade where specified in the following:

Four-stroke outboard motors: Honda®, Mercury®, Suzuki®, Evinrude/Johnson®, Bombardier/BRP®, Yamaha®, Nissan®, Tohatsu®

Inboard and I/O: Mercruiser®, Volvo Penta®, OMC®, Chrysler® Marine, Crusader®, Marine Power®, Chevrolet®, Ford®

Personal Watercraft: Honda®, Yamaha®, Bombardier/BRP® (Sea Doo®), Polaris®

For inboard motor applications, drain intervals may be extended to two times the engine manufacturer recommended interval or one year, whichever comes first.



Kinematic Viscosity @ 100°C, cSt (ASTM D-445)


Kinematic Viscosity @ 40°C, cSt (ASTM D-445)


Viscosity Index (ASTM D-2270)


CCS Viscosity, cP @ (°C) (ASTM D2602)

6871 (-25)

Flash Point °C (°F) (ASTM D 92)

234 (453)
Fire Point °C (°F) (ASTM D 92) 254 (489)
Pour Point °C (°F) (ASTM D 97) -46 (-51)

Noack Volatility, % weight loss (g/100g) (ASTM D-5800)


Four Ball Wear Test (ASTM D 4172 @ 40 kgf, 150°C, 1800 rpm, 1 hour, Scar in mm)

Total Base Number (ASTM D-2896) 10.5
HTHS (cP) 4.6
Humidity Cabinet Rust (ASTM D-1748) Pass

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