STIHL 4-MIX® engine technology

STIHL 4-MIX® engines offer excellent torque and fuel efficiency, all while still using the same 50:1 ratio fuel used in 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

Unlike other 4-stroke engines, the STIHL 4-MIX® engine uses the same fuel mix as a 2-stroke engine. This is petrol and oil in a 50:1 ratio, or a pre-mixed product such as STIHL MotoMix. This means that unlike a lawn mower engine, the machine can be used in any orientation as there's no seperate oil sump lubricating the engine. 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 too!

The STIHL 4-MIX® engine: how it works

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

Simple to start

Every STIHL 4-MIX® engine features 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 small valve in the engine cylinder. Some of the pressure escapes through this tiny opening, meaning that  less force is required to pull the starter cord. As soon as the engine speed reaches a set point, the  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

A 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 engine have been eliminated, such as oil pumps, oil filters and sumps. In addition to 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
Low scavenging losses Extremely fuel efficient
Higher RPM Lower RPM
Fast acceleration  High Torque

Summary: STIHL 4-MIX® engine:

  • Fuel efficient: 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