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The gas to oil mix ratio for a gas powered trimmer

By: Leon Rhodes

Modern gas powered grass trimmers with 2-stroke engines require a small amount of oil to be mixed with the fuel to prevent engine failure. If you add too much oil to the fuel the engine will billow clouds of smoke from the exhaust. If you add too little oil to the fuel the engine will overheat and, eventually, seize. Here's how to get the oil to gas mixture ratio right every time.

Trimmer Gas and Oil Mix Ratio

Important: 4-stroke grass trimmers do not need oil added to the fuel because they have a built in oiling system. Only add oil to two stroke engines that do not have a separate oil reservoir. If your trimmer has an oil reservoir you'll need to change the oil periodically, but never need to add oil to the fuel.

The proper gas/oil mix ratio for modern 2-stoke grass trimmers is 40 parts fuel to 1 part oil(40/1). You can purchase 2-stroke oil and mix it with regular gasoline yourself or buy pre-mixed 40-1 gas/oil anywhere that sells trimmers.

Save a little money by mixing it yourself

If you prefer buying pre-mixed fuel that's perfectly fine but it tends to be a little more expensive than mixing it yourself. I prefer to mix it myself because I can also control the octane of the fuel and limit the amount of small engine carb clogging ethanol in the mix. Here's how to properly mix it yourself.

  1. Get a clean fuel container that has markings on the side to tell you how full it is.

  2. Fill the fuel container with the gasoline of your choice EXACTLY to a gallon mark.

  3. A 40/1 ratio requires 113ml(3.2 ounces) of 2-stroke oil PER GALLON OF FUEL.

  4. That means if you have a full 2 gallon fuel container you will add 226ml(6.4 ounces) of oil

  5. For you Canadians using a container measured in liters the proper ratio is 25ml per liter

Important gas/oil mixing tips

Common gas/oil mix related questions

Which ratio has more oil? (40 or 50 to 1): A 40 to 1 fuel/oil mixture contains more oil than a 50 to 1 mixture. "1" represents the oil unit so the higher the other number the more diluted the oil is.

Is 2-stroke and 2-cycle the same thing?: Yes, both terms refer to the number of piston strokes per complete combustion cycle(one up for compression and one down for combustion), they mean the same thing.

Can I use 50 to 1 fuel/oil in a 40 to 1 engine?: Yes but it's not recommended. While it's better to use 50 to 1 fuel/oil if no 40 to 1 mix is available, instead of straight gas, over time increased engine wear will occur.

How long can 2 stroke fuel be kept?: 2 stroke oil has a shelf life of 5 years while unopened and 2 years once unsealed. After mixing 2 stroke oil with fuel the fuel can be safely stored for 2-3 months before it begins to degrade.

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