Why the right mix is critical
In a 2-stroke engine, the oil mixed with petrol is the only lubricant. There's no separate oil sump. If the mix is too lean on oil, the piston and cylinder aren't lubricated enough, leading to seizure (destroyed engine). If the mix is too rich, the engine fouls up, loses power, and the spark plug drowns.
The right ratio is therefore a vital balance between lubrication and clean combustion.
The ratios: conversion table
| Ratio | Oil per liter of petrol | Typical use |
|---|---|---|
| 50:1 | 20 mL | Modern standard (Stihl, Husqvarna, Echo, most current manufacturers) |
| 40:1 | 25 mL | Some Japanese models (Tanaka, older Shindaiwa) |
| 32:1 | 31 mL | Older models (pre-2000s) |
| 25:1 | 40 mL | Very old engines, some marine models |
When in doubt, use 50:1 with synthetic oil. It's the most widespread standard today. Always check your tool's manual — the ratio is indicated on the tool itself or in the instructions.
For common volumes
At 50:1 (most common):
- 1 liter of petrol → 20 mL of oil
- 5 liters of petrol → 100 mL of oil
- 10 liters of petrol → 200 mL of oil
At 40:1:
- 1 liter of petrol → 25 mL of oil
- 5 liters of petrol → 125 mL of oil
At 25:1:
- 1 liter of petrol → 40 mL of oil
- 5 liters of petrol → 200 mL of oil
Synthetic vs mineral oil
Synthetic 2-stroke oil (recommended):
- Better lubrication at high temperatures
- Cleaner combustion (fewer deposits)
- Allows leaner ratios (50:1)
- Price: 8-15 euros per liter
Mineral 2-stroke oil:
- Cheaper (4-8 euros per liter)
- Often requires richer ratios (40:1 or 32:1)
- Produces more smoke and residue
- Acceptable for occasional use
Never use: 4-stroke engine oil (10W-40, 15W-40...), used drain oil, or cooking oil. These oils don't mix properly with petrol and will destroy the engine.
