This particular gas and oil fuel mixture is used in STIHL string trimmers.

Your STIHL string trimmer must be maintained with the proper gas and oil in order to function at its peak.

Gas and 2-cycle engine oil are mixed in a fuel ratio of 50:1 for STIHL string trimmers. A 2-cycle engine oil that is certified to ISO-L-EGD and JASO M345 FD specifications is blended with unleaded fuel that has a minimum 89 octane rating and a maximum 10% ethanol content.

Use caution when working with gasoline and adhere to the STIHL operator’s manual’s safety recommendations. This includes using eye protection and working in a well-ventilated area.

String Trimmer Fuel Tank

String trimmers

Prior to diagnosing, repairing, or operating your equipment, make sure to follow all safety instructions provided in the operator’s manual. If you don’t have the knowledge, the skills, or the health to safely complete the repair, consult a professional.

Gas and Oil to Use in STIHL String Trimmers

At the moment, STIHL produces string trimmers with 4-MIX and 2-cycle engines. Each of these engine types needs a fuel mixture of gas and oil.

STIHL 4-MIX engines use a gas and oil mixture to maintain their compact form while combining the benefits of a 4-stroke engine. STIHL does not need a straight gas, in contrast to other 4-stroke engines on the market today.

STIHL 4-MIX string trimmer models:

  • FS 91, FS 91 R
  • FS 111, FS 111 R, FS 111 RX
  • FS 131, FS 131 R

Avoid ruining the engine of a STIHL 2-cycle or 4-MIX string trimmer by adding straight gas; you’ll likely need to purchase a new one.

When using straight gas, the engine will run very dry and seize up. The engine does not receive the lubrication it needs for internal parts to move freely if oil is not added to the gas.

STIHL String Trimmers Use a Gas to Oil Fuel Mixture of 50:1

STIHL’s 2-cycle engine or 4-MIX engine on the string trimmers has one fill port for a gas and oil mix. The mix ratio is required to be 50 parts gasoline to 1 part oil (50:1 Mix).

STIHL Gas to Oil Mix1 Gallon Gas2 Gallon Gas2.5 Gallon Gas
50:12.6 oz Oil5.2 oz Oil6.4 oz Oil
50:1 Gas to Oil Mix for STIHL String Trimmer

Type of Gas to Use in a STIHL String Trimmer

Always use new, unleaded fuel with a minimum octane rating of 89 and a maximum ethanol content of 10% to get the best performance out of your STIHL string trimmer.

When adding a fuel stabilizer to gas, you should use the fuel within 30 days and no later than 60 days because gas starts to break down as soon as 30 days after purchase.

Gasoline with an ethanol content attracts moisture from the air, which leaves a varnish in the fuel system. Gummy deposits will clog fuel system components and limit the carburetor’s ability to function.

This may cause issues with your STIHL string trimmer starting improperly, dying, or losing power.

Never use gasoline with a 10% or higher ethanol content, such as E15, E30, or E85. These fuels have ethanol content that ranges from 15% to 30% to 85%, respectively. The best fuels are those with little or no ethanol in them.

Type of Oil to Use in a STIHL String Trimmer

A premium 2-cycle oil that is ISO-L-EGD and JASO M345 FD certified is necessary for STIHL string trimmers. For your string trimmer, STIHL offers its own brand of oil: STIHL High Performance or STIHL HP Ultra.

As long as they are ISO-L-EGD and JASO M345 FD certified, you may also use other brands.

Automobile engine oil differs from two-cycle oil. Use only synthetic motor oil in your string trimmers.

Pre-Mixed STIHL 2-Cycle Fuel

Pre-mixed fuel is another way to run your STIHL string trimmer. This is a wise decision because it is ethanol-free.

Additionally, it is practical because it comes in a canister that can be kept on a shelf and is ready to use when needed. No mixing is necessary! Shake, then pour.

STIHL pre-mixed fuel is available at your neighborhood Ace Hardware or STIHL dealership.

ManufactureGas to Oil Mix2-Cycle OilPremixed Fuel
STIHL50:1High Performance
HP Ultra
STIHL String Trimmer Fuel Mix

How to Mix Gas for a STIHL String Trimmer

Decide how much fuel mixture you’ll need to make. To determine how much 2-cycle oil to add to the gas, refer to the chart above.

  • An authorized gas can’s cap should be removed.
  • Fill a gas can with unleaded fuel with a minimum 89 octane rating and a maximum 10% ethanol content.
  • Fill the gas can with the proper volume of 2-cycle oil.
  • Change the cap.
  • Shake the oil and fuel together slowly to combine them.
  • Fuel the string trimmer’s tank with more.

Mark your gas can with the type of gas or gas/oil mixture that is inside it at all times. A piece of equipment can sustain damage if the incorrect fuel