Gas-to-Oil Ratio for a Weed Trimmer

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A weed trimmer is a useful garden tool, especially if you live somewhere hot and humid where weeds tend to flourish. Weed trimmers run on a mixture of gas and oil, and two-cycle weed trimmers require a proper mix to run well. Too little oil and the engine will overheat and seize up. Too much oil and your engine will smoke, which can get the muffler all gummed up. Because weed trimmers do not have separate compartments for gas and oil, you must get the mix just right in order to ensure a healthy garden tool.

Gas-to-Oil Ratio for a Weed Trimmer
Image Credit: Sebastian Arning / EyeEm/EyeEm/GettyImages

The Right Mix

Most weed trimmers require oil to be added to the gas. Unlike engines that have separate gas and oil reservoirs, a weed trimmer's engine runs on a mix. This keeps the engine lubricated at all times. You should never use straight gas in a two-cycle engine because that will ruin it within minutes.

The make and model of your weed trimmer will determine the correct fuel-to-oil mixture. Some models require a ratio of 32:1, 40:1 or even 50:1. Check your owner's manual to make sure you're mixing the proper ratio. Otherwise, you could harm the engine.

Once you've figured out the correct fuel-to-oil ratio, it's simple to calculate the amount of gasoline and the amount of oil you will need. If your fuel-to-oil mix ratio is 40:1, for example, you will use 40 parts of gasoline to 1 gallon of oil. There is 128 oz. in a gallon. Divide 128 oz. by the mix ratio of 40, which equals 3.2 ounces of gasoline.

Shake It Up

Mix 3.2 oz. of engine oil with 1 gallon of regular gasoline. Because the oil will separate from the gasoline over time, thoroughly shake your oil and gas mixture before refueling your weed trimmer. Be careful when you do this so as not to get the oil and gas all over the place.

Use the Right Types of Fuel and Oil

Make sure to buy regular unleaded gasoline and not a diesel fuel. It's all right to use gasoline that is blended with a maximum 10 percent alcohol. If you want to use alternative fuels, such as ethanol or methanol, just be sure they are made up of a 10:2 ratio.

However, do not store the unit with this mixture inside. Alcohol-blended fuels can attract moisture and form acids. That can damage the fuel system. Also, keep in mind that fuels with more than 10 percent alcohol won't work well with your weed trimmer. They can decrease the power of the engine, causing it to run erratically.


Heather Skyler is a journalist and novelist who has written for wide variety of publications, including, The New York Times and SKY magazine.

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