Amsoil 10W-40 Synthetic Small Engine Oil

High heat can cause oils not formulated for severe service to boil off, leading to increased oil consumption, forcing the work crew to continually top-off the oil. Naturally Amsoil's 10W-40 solves this and much more!

SKU: ASF Category:

10W-40 Synthetic Small Engine Oil

10W-40 Synthetic Small Engine OilUsing a high-quality small engine oil has a direct effect on efficiency and profitability. Over time, wear and deposits rob small engines of power, reducing productivity. High heat can cause oils not formulated for severe service to boil off, leading to increased oil consumption, forcing the work crew to continually top off the oil. AMSOIL’s Synthetic 10W-40 Small-Engine Oil is a tough formulation designed to preserve engine power. You deserve to work more efficiently and save money on maintenance.

Product Code: ASF

Product Data Bulletin


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Fights Power Loss

Engine wear, carbon deposits, valve sticking and piston-ring sticking reduce engine power. AMSOIL Synthetic Small-Engine Oil prevents ring and valve sticking while helping eliminate carbon deposits from forming. As a result, engines produce maximum power throughout their service lives, helping you get more work done. After 500 hours of severe-service lab testing, AMSOIL 10W-30 (the 10W-40 works the same) Synthetic Small-Engine Oil virtually eliminated wear and deposits, helping preserve engine power and ensure productivity (see image).

Reduces Oil Consumption

Commercial-grade small engines run hot, with oil temperatures reaching 250ºF and higher. High heat causes standard-service oils to vaporize and exit the crankcase vent, leading to increased oil consumption. I mean look, it’s usually running with less than one quart. Heat also breaks down oil and forms deposits that lead to piston-ring sticking. Stuck rings fail to seal the combustion chamber and keep oil from entering and burning. As a result, workers must diligently check and top-off the oil to ensure the engine is protected, wasting even more time and money.
The AMSOIL Synthetic 10W-40 Small-Engine Oil’s heat-stable synthetic base oils withstand extreme heat better than other oils. In lab testing 10W-30 Synthetic Small-Engine Oil reduced oil consumption 48 percent compared to leading 10W-40 motor oils. It keeps engines clean for peak efficiency and reduced maintenance.

Long Service Life

On busy job sites, equipment maintenance can easily be delayed or overlooked completely. If using standard-service motor oils, high rates of oil consumption can leave the engine unprotected for extended periods, and it’s only a matter of time before catastrophic wear sets in. AMSOIL Synthetic Small-Engine Oil lasts longer than conventional oil, providing peace of mind that engines are protected, even when maintenance is delayed.

  • Preserves engine power
  • Helps cut maintenance costs
  • Fights heat and deposits

Applications and Recommendations

Use the appropriate viscosity of Synthetic Small-Engine Oil in applications that require any of the following specifications:

• API SL, SJ, SH, SG… (Gasoline)
• API CD, CF (Diesel)
• JASO MA/MA2 (Wet Clutch)

Use 10W-40 Synthetic Small-Engine Oil in small engines found in (not limited to) mowers (zero-turn, riding, stand-on, push), generators, power washers and other equipment that requires SAE 10W-40 or 15W-40 motor oil, including those made by Kubota, Kawasaki, Robin, Onan, Linamar and Vanguard.

Equipment types include maintenance equipment, tractors, lawn and garden equipment, compactors, pumps, light towers, log splitters, welders, cement mixers and trowels, skid-steers, excavators, rototillers and compressors.


AMSOIL Synthetic Small-Engine Oil is compatible with other conventional and synthetic motor oils. Mixing AMSOIL motor oils with other oils, however, will shorten the oil’s life expectancy and reduce the performance benefits.

Aftermarket oil additives are not recommended for use with AMSOIL motor oils.


AMSOIL Synthetic Small-Engine Oil is a long-life formulation that can last longer than conventional petroleum oils. It provides an extra measure of protection when equipment typically goes longer between oil changes than is recommended by the equipment manufacturer. Due to wide variances in operating conditions and maintenance practices, AMSOIL recommends extending drain intervals when monitored by oil analysis or following the equipment manufacturer-established drain intervals.


AMSOIL Synthetic Small-Engine Oil is Warranty Secure, keeping your factory warranty intact. AMSOIL Synthetic Small-Engine Oil is a high-performance replacement for vehicle
manufacturer-branded products and is also backed by the AMSOIL Limited Warranty. For details, visit If they tell you otherwise they gotta give you their oil for free!


This product is not expected to cause health concerns when used for the intended applications and according to the recommendations in the Safety Data Sheet (SDS). An SDS is available via the Internet at or upon request at (715) 392-7101. Keep Out of Reach of Children. Recycle used oil and bottle.

* All trademarked names and images are the property of their respective owners and may be registered marks in some countries. No affiliation or endorsement claim, express or implied, is made by their use. All products advertised here are developed by AMSOIL for use in the applications shown.

** Based on 125-hour lab tests of small engines using AMSOIL 10W-30 Commercial-Grade Synthetic Small engine Oil and three leading 10W-30/SAE 30 motor oils.

Equipment Storage

AMSOIL Gasoline Stabilizer (AST) should be used when fuel is stored for long-term, seasonal storage. For short- to medium-term storage, AMSOIL Quickshot® (AQS) is recommended.


Buy and Pricing


Best small engine oil
By  ALEX,  a  Verified Buyer  from  GA  on  November 19, 2021

I have run this oil for years in all of my commercial mowers. I have multiple with 1000’s of hours and have yet to have an engine failure. They get worked hard and the oil is still clean looking on the majority of them! Great product!
Great oil, but that’s about all Amsoil has to offer
By  LEE,  a  Verified Buyer  from  Dawson Pa  on  October 30, 2021

Their oil is really good, but they don’t offer anything else for Zero Turn Mowers. No oil filters etc.. I don’t know why, it’s a big market they are missing out on.
(From us:) Lee, yes we do in fact most of those filters you can cross them over to one of our oil filters. Our EA15K53 fits most Kohlers, yamaha and others. If not the EAOM103, EA15k09 and others will match. Use our oil filter cross reference tool or call our best dealer at 605-274-2580.
We also have all the grease, hydraulic oils, chain sprays, hydrostatic oil and more.
Generator oil
By  DAVID,  a  Verified Buyer  on  October 28, 2021

Use in RV 4K Onan generator, best protection you can get, easier to start in cold weather and superior protection in hot weather.
Extra Engine protection
By  PAUL,  a  Verified Buyer  on  October 10, 2021

I am a long time Amsoil user. This is my first time using the commercial grade because my local retailer didn’t offer it. I use it in all of my yard equipment because of the extra zinc and the added anti-wear protection it offers.
Local Dealer note: ^^ of course that know-it-all in the forums says all that is impossible for an oil to do so he’ll go on being the know-it-all forum guy.
Small Engine Insurance
By  Be,  a  Verified Buyer  from  Canada  on  September 03, 2021

The best oil for your small engine .Provides great insurance for your air cooled engine whether it is rough service or casual use. Get it.


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