STIHL 4-MIX® engine technology

STIHL 4-MIX® technology offers outstanding power in a lightweight design, and incorporates the best features of 2-stroke engines.

Sloping terrain in front of a house is cut with the STIHL FS 131 petrol brushcutter with 4-Mix® engine

STIHL 4-MIX®: the 4-stroke engine improved

The STIHL 4-MIX® engine has been developed in such a way that all of its functions support the user as effectively as possible. Unlike other 4-stroke engines, the STIHL 4-MIX® engine uses the same fuel mix as a 2-stroke engine – oil and petrol in a 1:50 ratio, or a ready-mixed product such as STIHL MotoMix. This means fewer parts and maintenance steps are required, facilitating a more compact design with less vibration and a very good power-to-weight ratio. The STIHL 4-MIX® engine achieves high torque with a comparatively low amount of fuel, making it a great low-emissions option. It’s also surprisingly quiet to use.

The STIHL 4-MIX® engine: how it works

The STIHL 4-MIX® engine is a 4-stroke engine that works by means of four actions, commonly referred to as suck, squeeze, bang and blow.

Simple to start

Every STIHL 4-MIX® engine boasts an integrated automatic decompression system to simplify the process of starting up the engine. When you start the 4-MIX® engine, centrifugal weights are used to open a valve in the engine a very small amount; some of the compression pressure can escape through this tiny opening, meaning that you need less power to start up the engine. As soon as the starter speed is exceeded by the first operating cycle, the automatic decompression system is automatically deactivated so the 4-MIX® engine runs efficiently and powerfully with full compression.

A woman wearing safety protection using a STIHL KM 131 R KombiEngine with blower attachment to collect leaves

The innovative 4-MIX® engine special design

The STIHL 4-MIX® engine is incredibly light. Because the engine is lubricated via the fuel-oil mix during operation, certain components that feature in conventional 4-stroke engines have been eliminated, such as oil pumps, oil filters and sumps. As well as making the engine lighter, the 4-MIX® design means that oil checks, oil changes and disposing of old oil are all a thing of the past.

STIHL 2-MIX or 4-MIX® engine?

Both of our flagship engine systems are innovative, powerful and extremely efficient. We’ve summarised the key features of the two systems in the table below.

STIHL 2-MIX engine STIHL 4-MIX® engine
Efficient fuel consumption The power available is applied as effectively as possible
Lower operating costs Can be used anywhere
Efficient propulsion Very high torque
Compact design Reduced pollution

Summary: STIHL 4-MIX® engine:

  • Fewer pollutants: as the fuel leaves very few residues when it combusts, the engine meets the requirements of the strict Euro V emissions standard
  • No oil service required: simple maintenance because the 4-MIX® engine uses the standard fuel-oil mix
  • Lightweight: as the engine is lubricated by the fuel mix, the 4-MIX® engine needs no oil pumps, oil filters and sumps that conventional 4-stroke engines include
  • Lower noise level: quiet operation even when it’s working hard
  • Engine power and high torque: high compression provides exceptional performance