AMSOIL Marine 4-Stroke Synthetic 10W-40 Engine OilExceeds NMMA “FC-W” Catalyst Compatible (Four Cycle-Water) Specification Requirements. Wet-clutch compatible for supercharged PWC engines.

Package sizes include:
1-Quart Bottle
1-Quart Bottles (case of 12)
55-Gallon Drum

AMSOIL 10W-40 Formula 4-Stroke Marine Synthetic Motor Oil is formulated for gas-powered outboard or inboard four-cycle boat engines as well as personal watercraft motors that require a 10W-40, 15W-40, 25W-40 or SAE 40.

Features and Benefits of AMSOIL 10W-40 4-Stroke Synthetic Marine Motor Oil

  • Robust wear protection
  • Resists hot operating conditions and heavy loads
  • Reduces friction
  • Fights deposit formation
  • Prevents internal rust and corrosion
  • Supercharger compatible
  • Reduces oil consumption
  • Capable of extended oil change intervals in some engine types (see below under “Service Life…”)
  • A excellent alternative to Mercury 25W-40 (see below)
  • Warranty approved carrying the NMMA “FC-W Catalyst Compatible” specification

World-Class Wear Protection for 4-Stroke Marine Motors

This 100% synthetic 10W-40 marine engine oil is loaded with design features that prevent wear during heavy loads, extended periods of full throttle and extreme heat. AMSOIL 10W-40 4-Stroke Marine will not lose its viscosity or breakdown during hard operation. Even if you don’t push your engine, this 4-stroke marine oil lowers friction, so it fights heat generation and improves efficiency. Protect your investment with AMSOIL from Oildepot.

Can Safely Replace Mercury 25W-40 Motor Oil

If you are looking for a safe, effective alternative for Mercury or Quicksilver 25W-40 marine engine oil, look no further than AMSOIL 10W-40 Synthetic Marine Motor Oil. We contend that this synthetic 10W-40 marine engine oil is not only a substitute for any conventional or synthetic 25W-40, it is actually an upgrade! How can a 10W-40 motor oil replace a 25W-40? We cover this topic extensively in our article What Can Replace Mercury 25W-40 Marine Engine Oil?

Engine Warranty ProtectionNMMA FC-W Catalyst Compatible Logo

AMSOIL 10W-40 Formula 4-Stroke Marine Synthetic Motor Oil carries the NMMA (National Marine Manufacturers Association) “FC-W Catalyst Compatible” specification, so your warranty is safe. AMSOIL Marine 10W-40’s NMMA Registration number is FC-00357P.

Anti-Rust and Corrosion Security

AMSOIL 10W-40 Formula 4-Stroke Marine Synthetic Motor Oil contains an anti-rust package that is vastly superior to that of ordinary motor oils. Engine internals and seals are protected from corrosion damage throughout the season and during long off-season storage periods.

Reduces Oil Usage

AMSOIL 10W-40 Formula 4-Stroke Marine Synthetic Motor Oil uses a shear-stable base oil the will not thin out or boil off in hot temperatures or under extended periods of severe service.

Suitable Applications for AMSOIL 10W-40 Formula 4-Stroke Marine Synthetic Motor Oil (gasoline engines only)

AMSOIL 10W-40 Formula 4-Stroke Marine Synthetic Motor Oil can replace the following viscosities in gasoline-powered engines:

  • 10W-40
  • 15W-40
  • 25W-40
  • SAE 40

Four-stroke outboard engines

  • Mercury
  • Honda
  • Yamaha
  • Johnson/Evinrude
  • Bombardier/BRP/Rotax
  • Suzuki
  • Nissan
  • Tohatsu

Four-stroke inboard and inboard/outboard (stern drive) engines

  • Mercruiser
  • Volvo Penta
  • OMC
  • Chevrolet
  • Chrysler Marine
  • Crusader
  • Marine Power
  • Ford

Four-stroke personal watercraft engines (including supercharged models)

  • Polaris
  • Sea-Doo (BRP)
  • Yamaha
  • Honda

AMSOIL 10W-40 Formula 4-Stroke Marine Synthetic Motor Oil is suitable for applications requiring the following specifications:

  • NMMA FC-W Catalyst Compatible
  • API SM

Service Life of AMSOIL 10W-40 Formula 4-Stroke Marine Synthetic Motor Oil

Four-Stroke Outboard Motors and Personal Watercraft
Change oil at intervals as suggested by your owner’s manual. Change oil filter at every oil change.

Inboard, Inboard/Outboard (I/O), Stern drive engines
Change oil at twice the interval as suggested by your owner’s manual or annually (whichever comes first)

Mixing AMSOIL Synthetic Marine Oil with Other Brands

AMSOIL 10W-40 Formula 4-Stroke Marine Synthetic Motor Oil is compatible with all other brands of conventional, semi-synthetic and synthetic boat engine oils. While you can safely mix AMSOIL Synthetic Oil with other brands, this will reduce the drain interval and performance capabilities of AMSOIL oil.

The use of any aftermarket oil additives is definitely NOT recommended.


SAE 10W-40, API SM, NMMA FC-W Catalyst Compatible

Kinematic Viscosity @ 100°C, cSt (ASTM D-445)14.1
Kinematic Viscosity @ 40°C, cSt (ASTM D-445)93.3
Viscosity Index (ASTM D-2270)155
CCS Viscosity, cP @ (°C) (ASTM D2602)6871 (-25)
Flash Point °C (°F) (ASTM D 92)240 (464)
Fire Point °C (°F) (ASTM D 92)254 (489)
Pour Point °C (°F) (ASTM D 97)-38 (-36)
Noack Volatility, % weight loss (g/100g) (ASTM D-5800)7.5%
Four Ball Wear Test (ASTM D 4172 @ 40 kgf, 150°C, 1800 rpm, 1 hour, Scar in mm)0.40
Total Base Number (ASTM D-2896)7.9
HTHS (cP)4.2
Humidity Cabinet Rust (ASTM D-1748)Pass
AMSOIL 10W-40 Formula 4-Stroke Marine Synthetic Motor Oil
A synthetic 10w-40 4-cycle boat engine oil designed to combat wear, friction and internal rust. Can replace Mercury Marine 25W-40.
Manufacturer: AMSOIL
Model: 10W-40 4-Stroke Marine Synthetic Motor Oil
Product ID: WCF