STIHL 4-MIX®: The 4-Stroke Engine Improved

Unlike conventional 4-stroke engines, the STIHL 4-MIX® engine uses the same fuel-oil mix as a 2-stroke engine (50:1 ratio), or a ready-to-use premix such as STIHL MotoMix.

This design means the engine can be operated in any orientation — without a separate oil sump — while delivering high torque, low fuel consumption, and exceptionally quiet performance.

The engine follows the classic four actions — suck, squeeze, bang, blow — with a unique bypass channel linking the valve train, crankcase, and intake. This allows the fuel-air mixture to continuously lubricate all key components.

• Intake: The piston moves down, drawing in fresh fuel mixture through the inlet valve.
• Compression: The piston moves up, compressing the mixture at the top of the cylinder.
• Ignition: The spark plug ignites the mixture, driving the piston down with high torque.
• Exhaust: Exhaust gases are expelled as the piston moves up again.

Because of this innovative layout, the 4-MIX® engine is self-lubricating and requires no oil changes.

Every STIHL 4-MIX® engine includes an automatic decompression system to make starting easier. When you pull the starter cord, centrifugal weights open a small valve in the cylinder, allowing pressure to escape — reducing resistance. Once the engine reaches operating speed, the valve closes automatically for full compression.

The 4-MIX® design eliminates traditional 4-stroke components such as oil pumps, filters, and sumps, resulting in a lighter engine that’s simpler to maintain. There are no oil checks or changes — and no need to dispose of old oil.

This makes STIHL’s 4-MIX® technology perfect for professional tools such as brushcutters, blowers, and KombiEngines, offering a great balance of power and efficiency.

• Fuel efficient: Meets Euro V emissions standards with clean combustion.
• No oil service required: Uses standard 50:1 fuel-oil mix, no separate oil needed.
• Lightweight: Fewer components mean less weight and simpler maintenance.
• Lower noise level: Operates quietly even under load.
• High torque performance: Exceptional power output with smooth operation.