Your manual wins. These are general practices. When your tool's manual says something different, follow the manual.
First: which engine do you have?
| Clue | 2-stroke (mixed fuel) | 4-stroke (straight gas) |
|---|---|---|
| Typical tools | Chainsaws, string trimmers, backpack and handheld blowers, edgers | Push and riding mowers, generators, pressure washers |
| Fuel cap | One cap, often marked "MIX" or with a fuel-and-oil symbol | Fuel cap only |
| Oil | No separate oil fill | Separate oil fill with a dipstick |
| Manual says | A ratio such as 50:1 | "Do not mix oil with fuel" |
A few handheld tools use 4-stroke-style engines that still run on mixed fuel. When in doubt, read the label on the fuel cap or the manual.
Mix ratios
2-stroke oil is mixed into the gasoline. The ratio means parts of gas to one part of oil.
| Ratio | Oil per 1 gallon of gas | Oil per 2.5 gallons |
|---|---|---|
| 50:1 | 2.6 fl oz | 6.4 fl oz |
| 40:1 | 3.2 fl oz | 8.0 fl oz |
| 32:1 | 4.0 fl oz | 10.0 fl oz |
| 25:1 | 5.1 fl oz | 12.8 fl oz |
Most current Echo, Stihl and Husqvarna handheld tools call for 50:1 with a high-quality 2-stroke oil. Older tools often call for 40:1 or 32:1. Use the ratio printed on your tool.
How to mix
- Use a clean, approved fuel can marked for mixed fuel.
- Pour in about half the gas, add all the oil, close it and shake.
- Add the rest of the gas and shake again.
- Label the can with the ratio and the date.
Gas: octane and ethanol
- Use the octane your manual lists (many handheld tools ask for 89).
- Use no more than 10% ethanol (E10). E15 and E85 are not allowed in small engines and can damage them.
- Ethanol-free gas or canned pre-mixed fuel stores longest and is easiest on seldom-used tools.
Storage
- Mixed fuel goes stale. Use it within about a month, or add fuel stabilizer when you mix.
- For storage over a month, run the tool dry or use stabilized or canned fuel.
- Never store fuel in the living space of a home.
Too much oil, too little oil
- Too much oil: smoky exhaust, oily buildup, fouled spark plug. Annoying, rarely fatal.
- Too little or no oil: the engine runs hot and can seize in minutes. This kills tools. If you put straight gas in a 2-stroke, drain it before starting.
Chainsaw bar oil is separate
Chainsaws have a second tank for bar-and-chain oil that lubricates the chain. It is not the same as the 2-stroke oil in the fuel. Fill both every time you fuel up.
Manufacturer instructions
Your tool manual is the final word. Find yours by model number:
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