That string trimmer sitting in your shed might look simple enough, but what you put in its tank can make the difference between years of reliable service and a costly paperweight. After seeing countless perfectly good trimmers ruined by fuel mistakes, I’ve compiled the most common blunders that even experienced users make. Avoid these, and your trimmer will thank you with smooth operation season after season.
1 Eyeballing the Mixture Instead of Measuring
We’ve all been there—in a rush to get the yard work done, squeezing some oil into the gas can and giving it a shake. “That looks about right,” you think. But here’s the brutal truth: your eyes are terrible measuring tools when it comes to precise ratios like 50:1 or 40:1.
This casual approach is a fast track to engine damage. Too little oil, and your engine components grind themselves to death without proper lubrication. Too much oil leads to carbon buildup, fouled spark plugs, and excessive smoke. I’ve seen both extremes ruin perfectly good equipment in a single afternoon.
Instead, use a proper measuring container or check a 2 stroke oil mix chart to get the exact amount needed for your specific ratio. These charts break down precisely how much oil you need per liter or gallon of fuel, eliminating the guesswork that kills engines.
2 Using the Wrong Ratio for Your Specific Trimmer
Not all string trimmers are created equal. While many modern models run on a 50:1 ratio (that’s 50 parts gas to 1 part oil), others might require 40:1, 32:1, or even 25:1. Using the wrong ratio is like feeding a dog cat food—it might eat it, but it won’t thrive.
I once helped a neighbor who couldn’t figure out why his new trimmer was running terribly. Turns out he was using the same 32:1 mix from his old trimmer, when the new one needed 50:1. The excess oil was causing all sorts of problems.
Always check your owner’s manual for the manufacturer’s recommended ratio. When in doubt, a quick online search with your trimmer’s make and model will usually turn up the answer.
3 Mixing Directly in the Fuel Tank
I’ve watched people pour gas into their trimmer tank, then add oil directly on top, assuming it will mix properly. This is about as effective as trying to mix oil and vinegar by pouring one on top of the other—it just doesn’t work.
The proper technique is to mix in a separate, clean container designed for fuel. Add the measured oil first, then the gas, seal it tight, and shake thoroughly. This ensures a proper mixture throughout the entire batch, protecting your engine from running on poorly mixed fuel.
4 Using Old or Contaminated Fuel
Gasoline starts to degrade after just 30 days, and the ethanol in most modern fuels attracts moisture from the air. That’s why that gas can that’s been sitting in your garage since last summer is your trimmer’s worst enemy.
I learned this lesson the hard way after my trimmer wouldn’t start after winter storage. The diagnosis? Gummed-up carburetor from stale fuel. The repair cost more than the trimmer was worth.
Always use fresh fuel, and only mix what you’ll use within a month. If you must store fuel, use a quality stabilizer and keep it in an airtight container.
5 Ignoring the Type of Oil Specified
That bargain-bin oil might save you a few bucks today, but it’ll cost you a new trimmer tomorrow. Two-stroke engines need specific oil formulated for air-cooled engines—not motor oil, not marine oil, and definitely not whatever random oil you have lying around.
Using the wrong type of oil can lead to poor lubrication, carbon buildup, and premature engine wear. Always use high-quality two-stroke oil that meets the specifications in your trimmer’s manual.
By avoiding these common mistakes, you’ll extend your string trimmer’s life significantly. Take the extra minute to measure properly, use the right materials, and mix correctly. Your trimmer will reward you with years of reliable service, and you’ll save money in the long run by not having to replace equipment prematurely.
