2-Cycle Oils


Most people think of 2-cycle engines as the small engines found in chain saws, leaf blowers, and string trimmers or larger versions found in snowmobiles and outboards.  These engines require either premixing oil with the fuel or have an injection system that takes oil from a tank to mix with the fuel. Many don’t realize that there are 2-cycle engines that are just as large as 4-cycle engines, maybe larger.  Detroit Diesel and other manufacturers have been manufacturing 2-cycle engines for decades that have oil sumps and valves and operate basically the same as a 4-cycle engine.  The main difference is that the 2-cycle engine gives you a power stroke every revolution whereas a 4-cycle engine produces a power stroke ever other revolution.

This post however is not intended to point out the pros and cons of the different types of engines but to talk about the oil used in the common, small 2-stroke engines specifically, the engines that use a premix of oil and gasoline.

Over the years, the mix ratio of fuel to oil has changed with the development of better lubricants and additives.  I used to have an old outboard that called for a 20:1 mix ratio.  That meant for 5 gallons of gas you needed a quart of 2-stroke oil.  (It also meant you got a lot of smoke.)  Over the years the ratios improved along with the engines.  32:1   40:1   50:1   The 50:1 ratio is probably considered the normal mix now.  At that ratio you still need almost 13 oz of oil to 5 gallons of gas.

While the oil is needed for lubrication, it has a few drawbacks.  Because it is burned with the fuel it can produce smoke.  What doesn’t get burned is expelled with the exhaust and has an environmental impact.  It can also add to carbon and varnish buildup inside the engine effecting performance and the life of the engine.  So the goal should be to use the least amount of oil possible.  Enough to provide proper lubrication without creating the smoke, carbon, varnish and the environmental impact.

AMSOIL has several 2-stroke oils designed for premix applications at a 100:1 ratio.  I could start giving technical information about these oils but I think the recent comments by Al Amatuzio, the founder of AMSOIL talking about product development explains more in a few paragraphs than all of the technical specs and reasons I could give you to use these products.


“Our second product, AMSOIL 2-Cycle Oil, was introduced in 1973.  Again, we challenged the status quo. I wanted our Dealers to have a product that out performed all others. It had to be the very best. At that time I was working with a highly specialized and competent additive supplier, and I knew very well that the additive used would be critical to wear protection. I would start with a pure synthetic base oil, but it would be the additive that carried the load.

As we began formulating, the supplier recommended the additive percentage that should be used.  I knew, at that percentage, it would be a good oil, but I wanted to push the limits.

 “How much higher can I go?” I asked. I could tell it was the first time he had ever been asked that question.

 “Higher,” he said, “why would you want to do that? It’s very expensive.”

 “Because I want to make a better oil,” I said.

 A week or so later the supplier got back to me with the maximum percentage that could be used. So that’s where I took it. We had the oil tested at Southwest Research at a mix ratio of 300:1. Keep in mind that the best anyone else was doing at that time was maybe 50:1. We were at 300:1 and passed with flying colors. We eventually introduced the oil at 100:1 because from a marketing perspective no one would have believed a 300:1 mix ratio.”

End Quote

AMSOIL has had the 100:1 mix ratio since 1973.  That’s 41 years and I still have people tell me you can’t run 2-cycle engines on that thin a mix.  Want to bet?  There are thousands of homeowners, landscapers, loggers etc that are doing it every day.  One comment I get quite frequently is “You can do it but you’ll burn out your engines.”

In the early 90’s when I first started selling AMSOIL products I talked to a local landscaper who had been using the 100:1 premix for years.  Not having any experience with 2-cycle oils at that time but knowing AMSOIL produced quality products I asked him what it was about AMSOIL that kept him using it.  His comment:

“Using the manufacturers oil at a 50:1 mix we’d get about 18 months out of a string trimmer before it died.  Using the AMSOIL 100:1 we usually doubled that and even have some that are pushing 5 years old.  As long as the operators take care of them and don’t physically beat them to death, they just keep running.” 

For those who believe that using a 100:1 mix will “Burn out your engine,” I believe the following information from a dealer in Wisconsin talking about chainsaws explains their misunderstanding of 2-cycle engines and lubrication.

I’ve found often times customers with 2 stroke engines confuse fuel/oil mix ratios with fuel/air mix ratios. Typically, an engine running lean (as in white spark plug) is running lean from the ratio of fuel to air – not the ratio of fuel to oil. I’ve never found a lack of oil to cause the spark plug to turn white – it will usually cause the piston to seize in the cylinder or damage needle bearings etc…

 Fuel air ratios are set with most 2-cycle engines by fuel adjustment screw or in some larger engines through changing jets for the fuel. You can’t change the air density or volume – so you have to adjust the fuel to match the air. In extremely cold conditions (especially when it is very cold and sunny – high barometric pressure), air becomes more dense and you may notice the color of the plug to start to lighten if the fuel screw is not adjusted to compensate.

 Over time, a carburetor can become dirty and fuel flow can be restricted causing the ratio to go lean (low fuel : high air volume) or through years of use a screw can be bumped or vibrate if the spring weakens etc… a number of factors can create rich or lean conditions of the air fuel ratio.

This can be confusing for customers, but on an older chainsaw I would suggest that it is far more likely his white plug and high temperatures are from the engine running a lean fuel to air ratio due to carb adjustment issues or a dirty carb.

 Note that in newer fuel injected engines fuel/air ratios are controlled by the engine’s computer and these issues mostly go away. Also, some newer chainsaws (Stihl) have computer controlled fuel/air mixtures that I would imagine are likely to also reduce these problems in the future. The computer will adjust for changes in air temp, humidity, and pressure.

Want the technical information on the AMSOIL 100:1 premix oils?

SABER Professional 2-Stroke Oil

SABER Professional (ATP) is specifically designed for handheld pre-mix two-stroke power equipment including, but not limited to, chainsaws, trimmers, blowers, brush cutters, edgers and shredder vacs. SABER Professional’s high-quality synthetic base oils burn more cleanly than other synthetic and conventional base oils. It eliminates carbon deposits that lead to stuck piston rings, clogged exhaust ports and plugged spark arrestor screens. Following 300 hours of professional-use testing in ECHO* string trimmers, SABER Professional mixed at 100:1 resisted carbon better than ECHO Power Blend* XTended Life* Universal 2-Stroke Oil mixed at 50:1 (see images). For complete test results, see the ECHO 100:1 String Trimmer Technical Study (G3470).

AMSOIL Outboard Synthetic 2-Stroke Oil

AMSOIL Outboard Synthetic 2-Stroke Oil (ATO) is specifically designed for pre-mix water-cooled two-stroke outboard motors, personal watercraft and jet boats. Specifically designed for outboard motors, Outboard 100:1 Pre-Mix Synthetic 2-Stroke Oil contains a heavy dose of low-temperature dispersant additives that excel at reducing varnish, carbon and deposit formation in water-cooled motors. Its low-smoke, low-odor, low-toxicity properties produce fewer emissions at 100:1 mix ratios than oils mixed at 50:1, benefiting operators and the environment. Outboard Synthetic 2-Stroke Oil is formulated to prevent “oil loading” and plug fouling for rapid throttle response, making it ideal for trolling motors.

AMSOIL also has excellent 2-Cycle Oils for Injector systems.

AMSOIL HP-Marine  Excellent for Evinrude® E-TEC™ factory-lean setting (replaces Evinrude XD100™ 2-Cycle Oil). Helps prevent deposits, protects against wear, has low smoke, protects against rust and has low aquatic toxicity. Superior performance as an injection oil or at 50:1 pre-mix.
High-quality motor oil is critical for maximum performance in modern two-stroke marine motors. Direct fuel injection (DFI) improves combustion efficiency, delivering the extra power enthusiasts want, while leaner gas-to-oil ratios provide the reduced exhaust emissions the government mandates. The leaner ratio leaves less oil to lubricate and protect these hotter, more powerful motors, which invites deposits and wear that threaten engine performance and life. HP Marine is proven to excel in these harsh conditions. It controls performance-robbing friction, heat and wear, yet produces low smoke and has low aquatic toxicity properties. It’s an oil as advanced as the engines it protects.

For more information check out the Marine E-Tec Field Study Report

AMSOIL Interceptor Synthetic 2-Stroke Oil

Two-stroke snowmobiles are meant to be ridden hard. Repeatedly pushing a machine to wide-open throttle during all-day, aggressive riding, however, takes its toll on the engine. INTERCEPTOR Synthetic 2-Stroke Oil is specifically designed for maximum performance in all makes of two-stroke snowmobiles, including Ski-Doo*, Polaris* and Arctic Cat*, helping enthusiasts spend more time riding and less performing maintenance. It is compatible with nearly all other two-stroke oils, while its low-smoke, low-odor properties help ensure riders won’t be “smoked out.” INTERCEPTOR is engineered to be pushed as hard as the sleds it protects.

For Ski-Doo® Rotax® E-TEC® Study, Click Here

DOMINATOR® Synthetic 2-Stroke Racing Oil – Racers can’t win what they don’t finish. That’s why AMSOIL formulators built DOMINATOR® 2-Stroke Racing Oil. This complex blend of oils and additives directly addresses the heat, pressure and friction of race-engineered engines. These engines operate on the edge, yet engine reliability is critical. DOMINATOR does an outstanding job protecting high-performance engines. It adds durability that professional racing teams depend on and delivers confidence so engines can be pushed to the limit.

AMSOIL Synthetic 2-Stroke Injector Oil – Strenuous conditions define the normal operating environments of snowmobiles and boats. Without the right lubrication, two-stroke snowmobile engines and outboard motors run hotter, accumulate deposits and suffer a reduction in performance. AMSOIL Synthetic 2-Stroke Injector Oil offers the convenience of one formula for the tough conditions of all two-stroke recreational equipment. It is tested and proven to minimize wear and deposits that can damage internal components. AMSOIL Synthetic 2-Stroke Injector Oil provides quality and affordability for cost-conscious enthusiasts who want the benefits of synthetic two-stroke oil.

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