Mixing 2-stroke oil requires a 50:1 ratio for STIHL equipment, which is 2.6 fl oz of oil per gallon of fresh gasoline.
Grab the wrong ratio and you risk scoring the piston or leaving carbon that chokes the exhaust. The correct way to mix 2-stroke oil isn’t complicated, but it does demand precision. The short version: measure the oil, pour it into an approved fuel can, add fresh gasoline, cap it, and shake. Below is the breakdown you actually need.
The 50:1 Mix Ratio, Explained
STIHL’s published guidance for its gasoline-powered equipment is 50 parts gasoline to 1 part oil. For a US gallon, that translates to 2.6 fluid ounces of 2-stroke oil. In metric, it’s 20 mL of oil per liter of fuel.
That ratio holds for every STIHL gasoline-powered tool in the lineup. The company’s technical documentation for the FS 131 and FS 131 R trimmers, for instance, specifies the same 1:50 mix with STIHL two-stroke engine oil.
One exception worth knowing: Stick with the maker’s oil and the 50:1 figure, and you’re on safe ground.
The Correct Mixing Sequence
Order matters more than most people think. Pour the oil into the container first, then add the gasoline.
- Measure the correct amount of 2-stroke oil based on your fuel volume.
- Pour the oil into an approved, empty fuel can. Never mix directly in the machine’s tank.
- Add fresh unleaded gasoline to the can.
- Seal the container and shake it vigorously until the oil is fully dispersed.
Adding oil first means the gasoline flow helps flush the oil out of the can’s spout and into the fuel, giving you a more consistent blend. The result should look uniformly tinted, with no oily streaks or layers floating on top.
Common Mistakes That Damage Engines
The biggest error is mixing fuel in the equipment’s own tank. Agitation is limited, and the ratio ends up uneven. Use a dedicated fuel can every time.
Fresh fuel is non-negotiable. Gasoline that sits too long loses its volatility and can leave varnish behind.
Using the wrong ratio is the other classic failure. Too little oil starves the moving parts of lubrication; too much oil fouls the spark plug and leaves carbon deposits. If you’re ready to stock up on the right lubricant, our roundup of the best two-stroke transmission oil options covers tested picks for your equipment.
One more distinction: these mixing steps apply only to gasoline-powered 2-stroke gear. Electric tools don’t use fuel mixtures at all.
| Fuel Volume | Oil Needed (50:1) | Best For |
|---|---|---|
| 1 US gallon | 2.6 fl oz | Typical trimmer or blower jobs |
| 5 US gallons | 13 fl oz | Multi-day or commercial use |
| 1 liter | 20 mL | Metric-measured fuel cans |
| 5 liters | 100 mL | Larger equipment runs |
FAQs
Can I Use Regular Motor Oil Instead of 2-Stroke Oil?
No. Standard motor oil doesn’t burn cleanly in a 2-stroke engine and will leave heavy carbon deposits that quickly foul the plug and exhaust port. Always use an oil specifically formulated for air-cooled 2-stroke engines.
How Long Does Mixed 2-Stroke Fuel Stay Fresh?
Mixed fuel is best used within 30 days. After that point, the gasoline begins to degrade and the oil can separate. Adding a fuel stabilizer before mixing extends the usable life, but it doesn’t make old fuel fresh again.
What Happens If I Use a 40:1 Mix in a 50:1 Engine?
The engine receives more oil than specified. That extra lubrication typically won’t destroy the engine immediately, but it increases smoke, risks fouling the spark plug, and can build up carbon over time. The reverse, using less oil, is far more dangerous.
References & Sources
- STIHL USA. “How To Mix Oil & Gas Guide.” Details the official 50:1 ratio and the correct mixing sequence for US gallons.
- STIHL Australia. “How to Mix 2-Stroke Fuel Correctly.” Confirms the 50:1 ratio and the 25:1 alternative for non-STIHL oils.
- STIHL Technical Document. “FS 131 / FS 131 R Instruction Manual.” Documents the 1:50 mix ratio for specific STIHL trimmer models.