2-Stroke Oil Mix — Frequently Asked Questions
[01] How much 2-cycle oil do I mix per gallon?
It depends on the ratio. At 50:1 add 2.56 oz of oil per gallon of gas; at 40:1 add 3.2 oz; at 32:1 add 4 oz; at 25:1 add 5.12 oz. The formula is simply 128 ÷ ratio = ounces of oil per gallon.
[02] What is 50:1 in ounces and millilitres?
A 50:1 mix is 2.56 fluid ounces of oil per US gallon of gas, or 20 ml of oil per litre.
[03] How much oil do I need for 5 gallons at 40:1?
At 40:1 you add 3.2 oz of oil per gallon, so 5 gallons needs 16 ounces of 2-stroke oil (that is one US pint).
[04] What happens if I put too much 2-cycle oil in the mix?
Too much oil makes the engine run rich: it can smoke heavily, foul the spark plug, build up carbon, and lose power. A little extra is far safer than too little, but stick close to the recommended ratio.
[05] Can I run 50:1 instead of 40:1?
Only if your engine and oil are rated for it. A 50:1 mix has less oil than 40:1, so running 50:1 in an engine that calls for 40:1 means less lubrication. Always follow the ratio in your owner's manual or on the oil bottle.
[06] Are 2-cycle and 2-stroke the same thing?
Yes. "2-cycle" and "2-stroke" are two names for the same engine type, where fuel and oil are pre-mixed. This calculator works for both.
[07] How do I know which mix ratio my equipment needs?
In order of authority: the decal on or near the fuel cap, then the owner's manual, then the manufacturer's published specification for that model and year. Only when all three are unavailable should you fall back on a general rule, and then the richer ratio (more oil) is the safer guess.
[08] Can I use car engine oil in a 2-stroke mix?
No. Two-stroke oil is formulated to be burned with the fuel and is low-ash, so it leaves minimal deposits. Four-stroke motor oil is designed to circulate and be retained, contains additives that do not burn cleanly, and will carbon up the exhaust port, foul the plug and eventually damage the engine.
[09] How long does mixed 2-stroke fuel last?
Plan on about 30 days for untreated pump gas premix, and longer with a fuel stabiliser or with ethanol-free fuel. Stale mix is the most common cause of a small engine that will not start after sitting, so mix in small batches and label the can with the ratio and the date.
[10] What oil rating should I look for on the bottle?
For air-cooled equipment (chainsaws, trimmers, blowers, dirt bikes) look for JASO FD, the highest of the JASO air-cooled grades, or ISO-L-EGD. For water-cooled outboards look for NMMA TC-W3, which is a different standard for a different engine environment. The two are not interchangeable.
[11] Do I mix in the gas can or in the machine's tank?
Always in an approved fuel can, never in the tank. Measure the oil into the empty can, add the gas second so pouring stirs the mixture, then seal the can and shake it before you fill the tank. Oil poured straight into a tank does not disperse, and the engine runs the first part of that tank almost unlubricated.
[12] What octane gasoline should I use for a 2-stroke mix?
Most manufacturers of handheld equipment specify 89 octane or higher, and ethanol-free fuel where it is available. Ethanol attracts moisture and degrades fuel lines and diaphragms in small carburettors, which is why premium ethanol-free fuel is worth the price difference for equipment that sits between uses.