Are Stihl Trimmers 4-Cycle? (Answered)

Stihl products are renowned the world over for their efficiency, durability, and overall reliability. The brand’s wide range of trimmers is certainly true to form and Stihl prides itself on always being ahead of the innovation curve.

Sthil makes its new and innovative 4-mix engine for its trimmers instead of the standard 4-cycle engine. It uses the best of the 2 and 4 stroke technology to create a quieter and more reliable user experience. With less vibration it lasts longer and with no oil changes, maintenance is easier.

Today we take a look under the hood, so to speak, as we zoom in on the engine technology behind some of our favorite Stihl weed whackers. Join in as we discuss the company’s patented “4-mix” engine, and some of the best machines it powers. Let’s get started!


Do Stihl Trimmers Have 4 Stroke Engines?

Stihl has always wanted to distinguish itself from the rest of the power tools market, with the company exploring every way of doing this. 

Stihl does not specifically make a 4 stroke or cycle engine for their trimmers. But they do make both 4 ‘mix’ and 2 stroke trimmers that are widely available on today’s market. The difference between a 4 stroke and 4 mix engine is based on the use of separate or mixed oil for lubrication.

Engine technology is one of the avenues Stihl has gone down in pursuit of this goal, and they have come up with some interesting results, particularly where weed whackers are concerned.

You see, on top of the 2-stroke trimmers we all know and love, Stihl also makes trimmers powered by something akin to a 4-stroke motor…that is not a 4-stroke motor. 


It’s quite simple. Stihl has pioneered a new type of engine known as the “4-mix”. These engines are similar to regular 4-stroke motors in terms of how they work. They incorporate the same engine piston pattern that involves:

  • An intake stroke
  • A compression stroke
  • A power stroke
  • An exhaust stroke

However, 4-mixes differ from regular 4-strokes when it comes to fuel. A 4-mix engine runs on a gas and oil mix, much like 2-stroke engines…hence 4 “mix”. 

As you know, 4-strokes run on gas or diesel, with oil added to a separate tank. Stihl 4-mix trimmers do not have separate oil tanks, so their engines’ lubricative needs are met by the oil in the mix.

I recommend this round trimmer line found on Amazon for your 4-mix Stihl trimmer.

To read more about trimmers and other lawn equipment, I recommend my other articles here..

What Is A 4-mix Engine?

For those still skeptical of the difference, I will go into detail of the combined nature of a 4-mix engine. There are elements of both 2 and 4 stroke versions.

A 4-mix engine is a combustion motor invented by Stihl to power various tools including leaf blowers, lawn edgers, and, of course, trimmers. This engine mimics the operation of a 4-cycle engine, but uses oil for lubrication mixed with the fuel like a 2 stroke engine.

The 2-stroke motor was once the company’s bread and butter but, due to certain inefficiencies and increasingly stringent environmental laws, company heads decided to pivot to the 4-stroke…but with a twist.

The result was an engine that could combine the best attributes of 2-stroke and 4-stroke technology. As we’ve already seen above, the 4-mix combines the fueling of the former with the operation of the latter.

Let’s start by looking at the composition of a Stihl 4-mix engine. As far as parts go, you have everything you would expect in a 4-stroke engine. You have your: 

  • sparkplug
  • inlet/exhaust ports and valves
  • pushrod passages 
  • bypass bore
  • valve gear
  • crankcase and crankshaft
  • piston
  • combustion chamber

The 4-mix also has a few advantages over traditional 2 and 4-stroke motors.

The main advantage is arguably its low environmental impact. The 4-mix boasts lower exhaust emissions and noise levels than your average 2-stroke engine. Gone are the days of circumventing neighborhood noise hours or environmentalist watchdogs.

Like a 2-stroke engine, the 4-mix has a very quick start and high RPM, which enables you to get your work done much more quickly. The 4-mix is compact, yet powerful thanks to its impressive power-to-weight ratio. The lack of an oil tank, oil pump, and sump greatly reduce the engine’s overall weight without compromising power output.

People who have previously owned 2-stroke Stihl products will be glad to know that the 4-mix uses the same 50:1 gas and oil mix. What’s not the same is the efficiency with which the 4-mix utilizes the fuel. 

The advantage 4-mix motors have over regular 4-strokes is the fact that 4 -mixes do not require oil changes. Since 4-mix motors get their lubrication from oil in the fuel mix, there is an almost zero percent chance of you ever forgetting to top up your oil.

Another highlight is the reduced vibrations, especially when compared to 2-stroke engines. This facilitates greater engine longevity, which will save you the long-term cost of getting a new trimmer. 

How Does A 4-mix Stihl Engine Work?

A 4-mix engine works pretty much the same way as a regular 4-stroke engine, with a few notable differences.

Let’s take a look at a 4-mix’s combustion cycle.

The Intake

The first stage is known as the intake (or induction) stroke. This is when the piston (which is driven by the crankshaft) moves down the combustion chamber in the cylinder. When this happens, the fuel mix from the carburetor, as well as air, is sucked into the chamber.

Unlike with regular 4-strokes, a 4-mix engine utilizes a bypass bore that allows some fuel mix to reach all moving parts in the cylinder and crankcase. This is necessary for oil (the lubricant) to reach these parts and save them from grinding against each other.

When the piston moves down the cylinder and towards the crankcase, overpressure is created. This overpressure forces any fuel mix below the piston into the pushrod passages so it can circle back to the combustion chamber. This is necessary for the full utilization of fuel and lubrication of all engine parts.

The Compression

Next is the compression stage, which is when the inlet and outlet valves are closed to prevent air or fuel from escaping. At this stage, the piston moves up the cylinder and compresses the fuel and air mix up towards the sparkplug.

Power Stage

Compression is immediately followed by the power stage. When the cylinder reaches maximum compression, the sparkplug emits a spark to ignite the fuel and air mix. 

The explosion that ensues is known as combustion, and it forces the piston down the cylinder once again. Like with the intake stage, the piston forces overpressure. Any fuel remaining in the crankcase moves back to the combustion chamber.

The Exhaust Stage

Finally, we have the exhaust stage. This is when the exhaust port and valve open up just as the piston reaches the bottom of the cylinder. The inlet valve remains closed at this stage.

After combustion, smoke and gases linger in the combustion chamber. When the piston moves up the cylinder again, these gases are expelled from the cylinder via the exhaust port and released into the outside atmosphere.

Once the exhaust stage is complete, the cycle can begin all over again.

Which Stihl Trimmers Are 4-mix?

To say that the 4-mix has been a hit would be a massive understatement. Stihl is rapidly incorporating this awesome engine technology into most of its new products in a bid to stay ahead of the competition. Along with electrical power, the 4-mix is also the company’s ticket to a greener future.

So, which machines use this engine?

Well, for starters, we have the FS 91 R, a commercial weed eater that will help you tackle big projects without harming the environment. This machine is unbelievably powerful (1.27 horsepower) despite weighing only 5.5lbs!

The FS 91 R makes use of a straight-shaft design that is stylish and ergonomic. The loop handle is grippy, premium to the touch, and the perfect way to handle this lightweight marvel. You also get a simple three-step startup, which will help you get your de-weeding sessions up and running quickly.

Another trimmer sporting the 4-mix is the FS 131 R, another commercial trimmer for your landscaping business. This 1.9 horsepower straight shaft gem boasts many of the same features as the FS 91 R discussed above. You also get Stihl’s patented IntelliCarbTM Compensating Carburetor, which helps regulate RPM when normal air intake levels are disrupted.

The F131 R also boasts a fully lined driveshaft, which makes it one of Stihl’s best trimmers when it comes to low vibrations. You also get a corrosion-resistant polymer housing, a protected choke lever, and a shoulder strap for better weight (12.1lbs) distribution. 

Other notable 4-mix trimmers include:

The Final Touches On Stihl 4-mix Trimmers…

For those that wanted to know about a 4 stroke option for the popular Stihl brand of trimmers, the 4-mix option delivers more than expected. With quieter operation, better reliability, and less maintenance to remember, the 4-mix combines the best of 2 stroke and 4 stroke trimmers and surpasses them.

If you are familiar with Stihl products, you know that quality is built into the design. Now with this new innovation, they have outdone themselves.

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Mathew Booe

Mathew has worked in landscaping professionally for over 10 years. He is a grandpa and frequently interviews other experienced landscapers and lawn care experts who are also grandpas for these articles.

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