AMSOIL 10W-40 100% Synthetic Small-Engine Oil Delivers commercial-grade protection and outperforms conventional oils. Tough formulation protects against wear, heat, and carbon deposits. Helps maintain power and promotes long engine life. Specifically designed for maximum equipment dependability. Service life up to 200 hours.
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Product data sheets
View, download, or save a copy of the Product Data Sheet or Safety Data Sheet for AMSOIL 10W-40 100% Synthetic Small-Engine Oil.
AMSOIL 10W-40 100% Synthetic Small-Engine Oil is a commercial-grade, fully synthetic 4-stroke oil engineered for hot-weather and high-load outdoor power equipment that calls for an SAE 10W-40 or 15W-40 grade. The formulation is built for mowers, generators, pressure washers, log splitters, and similar equipment, and is the right choice for landscapers, contractors, and homeowners who want longer service life and stronger protection than a relabeled automotive oil can deliver.
Shear-stable wear protection
Small engines run under constant load and rely on a thick, durable oil film to keep metal surfaces apart. The 10W-40 is a shear-stable, high-film-strength formulation fortified with anti-wear additives that does not thin out under mechanical shear, ensuring a continuous lubricating film that protects against metal-to-metal contact. Four-Ball Wear Testing per ASTM D4172B returns a 0.45 mm wear scar for the 10W-40 grade, indicating strong boundary protection in the bearing and ring zones that take the heaviest load.
Heat-resistant base oils and low oil consumption
Air-cooled small engines run hotter than liquid-cooled automotive engines and burn more oil when the base oil flashes off. The 10W-40 uses heat-resistant synthetic base oils with low volatility, posting NOACK Volatility of 3.7 percent weight loss in ASTM D5800 testing. Lower volatility means less oil burned and a cleaner combustion chamber. In 125-hour lab tests of AMSOIL 10W-30 Synthetic Small-Engine Oil against three leading 10W-30 and SAE 30 motor oils, the synthetic small-engine formulation reduced oil consumption 61 percent, a family-wide benefit driven by the same heat-resistant chemistry used in the 10W-40.
Power preservation and deposit control
Engine power is reduced by wear, carbon deposits, and stuck rings and valves. The 10W-40 prevents ring and valve sticking and helps eliminate carbon deposit formation so engines produce maximum power across their service lives. After 500 hours of severe-service testing in a Kawasaki FX 730V engine, the piston and rings remain virtually free of deposits and wear. Saturated synthetic base oils and potent antioxidants resist extreme heat, while detergents fight carbon, varnish, and sludge to extend engine life.
Viscosity stability for hot-weather service
The 10W-40 grade is built for higher operating temperatures than 5W-30 or 10W-30 small-engine oils. Kinematic viscosity at 100 C is 14.5 cSt with a Viscosity Index of 156 per ASTM D445 and D2270, supporting a thicker high-temperature film for engines in hot climates, continuous full-load duty, or commercial cutting service. High-Temperature High-Shear viscosity at 150 C measures 4.4 cP per ASTM D4683, the durable hydrodynamic film called for in heavy-duty 4-stroke power equipment.
Cold-weather flow and rust protection
Even hot-climate equipment sees cold starts in early spring and on cool mornings. The 10W-40 has a naturally high viscosity index and contains no paraffin waxes, so it remains fluid at low temperatures. Pour Point is -39 C (-38 F) per ASTM D97 and CCS Viscosity is 6,057 cP at -25 C per ASTM D5293, supporting easier cold-weather starts and fast startup lubrication. Rust and corrosion inhibitors protect cylinder bores during off-season storage in damp sheds and trailers.
Commercial-grade formulation
Many small-engine oils on the market are relabeled automotive oils tuned for fuel economy. The 10W-40 is engineered for the demands of small engines, with a fortified additive package that targets wear, power loss, oil consumption, carbon deposits, and stuck rings and valves. The oil contains no friction modifiers and meets JASO MA and MA2 wet-clutch standards, helping prevent misapplication when the same bottle is used across mowers, generators, and certain transmissions.
Recommended applications and service intervals
AMSOIL 10W-40 100% Synthetic Small-Engine Oil is built for gasoline 4-stroke engines and certain off-road diesel engines that require any of the following service categories: API SL, SJ, SH, SG (gasoline), API CD, CF (diesel), and JASO MA or MA2 (wet clutch). It is intended for zero-turn, riding, stand-on, and push mowers, generators, power washers, and other similar equipment that requires SAE 10W-40 or 15W-40 motor oil, including engines made by Kubota, Kawasaki, Robin, Onan, Linamar, and Vanguard.
Service life: up to 200 hours or one year, whichever comes first, in severe-service small-engine duty, based on extensive severe-service testing.
Use only in equipment that specifies SAE 10W-40 or 15W-40. For SAE 30, 5W-30, or 10W-30 applications, choose the matching small-engine grade.
Aftermarket oil additives are not recommended for use with AMSOIL Synthetic Small-Engine Oil.
Outside the United States and Canada, follow the equipment manufacturer's recommended drain interval.
The 10W-40 is compatible with other synthetic and conventional motor oils, but mixing shortens oil life and reduces performance benefits, and extended drain intervals are not supported when oils have been mixed. Pair the oil with a fresh small-engine oil filter at every change to take full advantage of the extended interval.
Typical technical properties
Property
Value
Kinematic Viscosity at 100 C, cSt (ASTM D445)
14.5
Kinematic Viscosity at 40 C, cSt (ASTM D445)
96.6
Viscosity Index (ASTM D2270)
156
CCS Viscosity, cP at -25 C (ASTM D5293)
6057
Pour Point, C (F) (ASTM D97)
-39 (-38)
Flash Point, C (F) (ASTM D92)
232 (450)
Fire Point, C (F) (ASTM D92)
252 (486)
Four-Ball Wear Test, scar, mm (ASTM D4172B at 40 kg, 75 C, 1,200 rpm, 1 hr)
0.45
NOACK Volatility, percent weight loss (ASTM D5800)
3.7
High-Temperature High-Shear Viscosity at 150 C, cP (ASTM D4683)
4.4
Total Base Number
8.5
Order AMSOIL 10W-40 100% Synthetic Small-Engine Oil
The 10W-40 is available in quart (ASFQT-EA), case of 12 quarts (ASFQT-CA), gallon jug (ASF1G-EA), 5 gallon pail (ASF05-EA), and 55 gallon drum (ASF55-EA). All AMSOIL lubricants and filters are covered by the AMSOIL Limited Warranty, and the formulation is Warranty Secure, keeping the equipment manufacturer warranty intact when used in place of branded service oil. Match the right grade to the equipment with the AMSOIL Vehicle Lookup Guide, compare viscosities and applications in the Small Engine Oil Guide, then order AMSOIL 10W-40 100% Synthetic Small-Engine Oil.
SAE 10W-40 small-engine oil is a 4-stroke synthetic oil for outdoor power equipment that runs in higher ambient temperatures or under heavy continuous load. AMSOIL 10W-40 100% Synthetic Small-Engine Oil is intended for zero-turn, riding, stand-on, and push mowers, generators, power washers, and similar equipment that requires SAE 10W-40 or 15W-40 motor oil, including engines made by Kubota, Kawasaki, Robin, Onan, Linamar, and Vanguard.
Is synthetic oil good for small engines?
Yes. Synthetic base oils have a higher viscosity index, lower volatility, and better thermal stability than conventional oils, which directly addresses the heat, full-load duty, and oil burn-off that wear small engines down. The 10W-40 grade combines those base oils with anti-wear additives, antioxidants, and detergents engineered for air-cooled 4-stroke service.
Is small-engine oil different from car oil?
It can be. Many bottles labeled for small engines are simply relabeled passenger-car oils tuned for fuel economy. AMSOIL 10W-40 100% Synthetic Small-Engine Oil is built specifically for the conditions small engines see: higher heat, constant load, dirt and moisture exposure, and longer hours between service. It contains no friction modifiers and meets JASO MA and MA2, which are not required of automotive oils.
Can 10W-40 be used in a lawn mower?
The 10W-40 is intended for mowers and other 4-stroke outdoor power equipment that specifies SAE 10W-40 or 15W-40. For an engine that calls for SAE 30, 5W-30, or 10W-30, use the matching small-engine grade rather than the 10W-40. Verify the correct viscosity for the specific mower with the AMSOIL Vehicle Lookup Guide.
How long can the 10W-40 stay in service?
AMSOIL 10W-40 100% Synthetic Small-Engine Oil supports a service life of up to 200 hours or one year, whichever comes first, based on extensive severe-service testing of the synthetic small-engine family. It provides an extra measure of protection when equipment goes longer between oil changes than the equipment manufacturer recommendation.
Will using AMSOIL synthetic oil void a small-engine warranty?
No. Using AMSOIL synthetic lubricants does not void a new equipment manufacturer warranty. The 10W-40 is Warranty Secure and is covered by the AMSOIL Limited Warranty when used as a replacement for branded service oil.
Can the 10W-40 be mixed with conventional small-engine oil?
The 10W-40 is compatible with other synthetic and conventional motor oils, but mixing shortens oil life and reduces performance benefits. Extended drain intervals are not supported when oils have been mixed, and aftermarket oil additives are not recommended for use with AMSOIL Synthetic Small-Engine Oil.
