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Stale Gas Could Be Killing Your Small Engine

Updated: Jul. 02, 2018

Small-engine mechanics tell us that stale gas is what keeps them employed and busy.

FH14JAU_KILLER_01-2Family Handyman
Stale gas causes the vast majority of starting problems, which usually lead to a carburetor rebuild or replacement ($100). But if you follow a few simple rules, you can avoid hard-starting hassles and repair costs. Here's how.

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Buy smaller quantities

Buy smaller quantities

As with any product that has a limited shelf life, you should buy only what you need for the near future. If you buy ethanol (oxygenated) gas, buy only enough gas to last for 30 days. If you buy non-oxygenated gas, limit your purchase to a 60-day supply. To find a source for non-oxygenated gas near you, go to

With either type of gas, use a container that’s sized for the amount you’ll buy. Storing 2 gallons in a 5-gallon container leaves you with 3 gallons of air, causing the gas to spoil faster – even if it’s been treated with fuel stabilizer. Add the old gas in small quantities to your car or take it to the recycling center.

Add stabilizer every time you fill

Add stabilizer every time you fill

Many people add gasoline stabilizer only when they put the mower away for the winter. That’s a good idea, but that’s not the only time you should use stabilizer. Stabilizer works best when it’s added to fresh gas right at the pump. That way it can start working immediately to prevent trouble. And, since small-engine gas tanks are vented, adding pre-stabilized gas to the tank can reduce the effects of water accumulation and slow the loss of volatile vapors. Look for a stabilizer product that includes antioxidant protection, corrosion inhibitors, detergent and metal deactivators (Briggs & Stratton Advanced Formula Fuel Treatment & Stabilizer and STA-BIL are two examples.) If you have a two-stroke engine, buy oil with built-in stabilizer.

Get a new gas container

Get a new gas container

If your gas container doesn’t seal properly, you’re going to have gas problems. As the air temperature rises and falls, a poorly sealed container emits gas vapors and pulls in moisture. So you lose the most volatile ingredients in the gas – the ones you need most to start a cold engine. Also, the humidity that gets sucked in condenses on the container walls and falls to the bottom. As you reach the gas at the bottom, you’re literally pouring in a blend of old gas and water. If your old container is missing caps, buy a new one.

Filling and storage tips

Let the engine cool after use and then refill the tank to 90 percent. That will reduce moisture condensation and oxidation.

Consult your owner’s manual for off-season storage recommendations. Most manuals specify ‘dry storage,’ which involves draining the tank and running the engine until it dies. Then pull the cord until you get no signs of life from the engine. If the manual recommends ‘wet’ storage, fill the tank to 90 percent with fresh stabilized gas.

Use the right kind of gas

Never use E-85 or E-15 gas in your small engine. Those fuels can cause catastrophic damage.

Most small engines operate best with 87-octane fuel (85-octane in high altitudes). Unless specifically recommended by the manufacturer, never use a higher octane fuel in your small engine.

Choose long-life gas for occasional use

Choose long-life gas for occasional use

If you use less than a gallon of gas during a season, long-life gas in quart cans may be your best option. It’s non-oxygenated gas with stabilizer and specially formulated to keep its volatility and fire up right away, even after two years. Long-life gas is pricey but worth it if it saves you just one repair bill. It’s available at most home centers and small-engine shops.

Is ethanol why your engine won’t start?

Everybody blames oxygenated fuel (gas with ethanol) for carburetor failures. But guess what caused the problems before we started adding ethanol? Yup-stale gas. We’re not saying that gas with ethanol is the perfect fuel. It’s not. But the truth is, whether you buy oxygenated or non-oxygenated gas, operator error is really the root cause of carburetor corrosion and gunk buildup. Gasoline simply goes bad, and it goes bad faster if it’s improperly handled and stored. You can avoid all gasoline-related starting problems by following these simple buying, storing and usage tips.