A string trimmer is an important tool used in your yard maintenance routine. It’s important to service your trimmer regularly and use the correct oil to keep it in good condition.

While most string trimmers on the market today use 2-cycle engines, there are some models that use 4-cycle engines. Not using the right oil in your type of string trimmer can ruin the engine making it unrepairable.

2-cycle string trimmers require a gasoline and oil mix consisting of unleaded gasoline with a minimum octane rating of 89 and a maximum ethanol content of 10% and a 2-cycle premium oil that is ISO-L-EGD and JASO M345 FD certified. Most 4-cycle string trimmers require an engine oil of 10W-30.

You can find recommended gas-to-oil mix ratio by the manufacturer for 2-cycle string trimmers and recommended oil by the manufacturer for 4-cycle engines below. Take all safety precautions when working with oil and your string trimmer in your operation’s manual.

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Follow all safety instructions provided in your equipment operator’s manual prior to diagnosing, repairing, or operating.Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.

This is the Oil to Use in a 2-Cycle String Trimmer

A 2-cycle (2-stroke) engine requires oil to be added to the fuel used in the string trimmer. This fuel and oil mixture is added to the fuel tank.

Without adding oil to the gas, the engine will not receive the lubrication it needs for the engine parts to move freely. Running straight gas through a 2-cycle engine will cause the engine to seize and no longer work.

A 2-cycle engine in a string trimmer uses gas and oil mixed at a ratio of 50:1, 40:1, or 32:1. For example, 50:1 mix equals 50 parts gasoline to 1 part oil.

The mix your string trimmer requires varies by manufacturer. You can find the correct ratio in your operator’s manual. You may also find it located on the fuel cap.

To create the fuel mix, use these two items:

• Unleaded gasoline with a minimum octane rating of 89 (mid-grade) and maximum ethanol content of 10%. Never use a fuel with a higher content than this. The lower the ethanol content the better.
• 2-cycle premium oil that is ISO-L-EGD and JASO M345 FD certified.

2-Cycle Gas and Oil Mix Ratio in a String Trimmer by Manufacturer

Amount of 2-Cycle Oil to be Mixed with Gasoline for a String Trimmer

How to Mix Gas and Oil for a 2-Cycle String Trimmer

• Use the chart above to determine how much fuel mix to prepare.
• Remove the cap from an approved gas can. Add unleaded fuel (minimum 89 octane rating & maximum 10% ethanol content) to a gas can. I like to use a can that is the size of the amount of mix I am preparing. Clearly mark the can with “2-Cycle Mix” so you or others don’t add it to the wrong equipment.
• Using the chart for ounces of oil required to add to your amount of gas. Add the 2-cycle oil to the gas can.
• Replace the cap.
• Gently shake the fuel and oil until they are mixed.
• Add to the string trimmer’s fuel tank.

2-Cycle Premixed Fuel

A great option to reduce fuel problems and extend engine life is using an ethanol-free fuel mix. Many manufacturers offer their own brand of premixed fuels.

This is an ethanol-free blend of oil and fuel that is ready to pour into your string trimmer’s fuel tank. This is a convenient item to keep on the shelf.

You won’t have to deal with the bad effects of ethanol as discussed in the fuel section. Also, it’s convenient to have fuel available on your shelf when you need it. TruFuel also makes a good 40:1 premixed fuel or 50:1 premixed fuel.

This is the Oil to Use in a 4-Cycle String Trimmer

String trimmers that run 4-cycle (4-stage) engines have a fill port for engine oil and a fill port for gasoline. Never mix oil and fuel together for a 4-cycle engine. Also, never use 2-cycle oil in a 4-cycle string trimmer. Good engine oil is required.

Oil is required to keep the engine components lubricated. When the wrong type or not enough oil is used, friction can build in the engine and overheat causing your string trimmer not to start and possibly ruin the engine.

The engine oil viscosity may need to be changed to one better suited for very hot or very cold ambient temperatures when you are using your string trimmer in these types of conditions.

4-Cycle Engine Oil Viscosity Required by the Manufacturer