When good gas goes bad.

The fuel fueling your dirt bike or ATV doesn't last forever (one reason to ride!) but unless you have mathematical wizardry as a talent you likely end up with leftovers after the latest trip to the track or trails that might sit in the garage for the next few months.

Most people do not like throwing anything out that works or even remotely continues to function. A shirt with a hole in the arm pit? Perfectly fine. Rusted out lawn mower? As long as it cuts, no problem. OK, how about a gallon and a half of gasoline? You mean liquid gold? Actually, gas doesn't cost that much. Of course fueling a 20 gallon rig takes some dollars out of your wallet but the gas used for a day of riding probably ranks near the bottom in terms of all the expenses that add up.

Despite that, dumping perfectly fine fuel down the drain (relax - we mean this figuratively) borders on blasphemy for some people but using old gas in your dirt bike or ATV could do much more harm than losing the few bucks originally spent on the unused gas. But is old gas really that bad and just how old is old?

When Does Gas Go Bad?

First, gas indeed goes bad. The best part of fuel eventually evaporates making it burn less effectively in the engine. Therefore, old gas has lost some mojo, i.e. vital engine-running components, so bad gas, or old gas, affects performance. You could damage some parts running old gas but once burned off or even mixed with fresh gas you probably won't see any ill effects.

However, longer standing gas oxidizes and what was once gas no longer functions as gas. Eventually, the liquid fuel thickens and clogs up fuels lines and anything else gas flows through in the engine. Prevent this by draining the fuel tank or adding fuel stabilizer. But what about the plastic gas can sitting in the corner of the garage? Months after your last ride the jug of leftover fuel remains. It still sloshes around. A quick sniff offers a just filled smell.

So can you use it?

Since many factors determine how quickly gas goes bad including how fresh it was to begin with, the quality, ethanol content and how well sealed the container, the leftover gas from last season might fire your dirt bike right up. You'll know right away if it has oxidized but if you carry veteran rider status and follow the often repeated advice on the MotoSport blog you hopefully added fuel stabilizer to it before the longer winter break. If you added the stabilizer go ahead and use the gas.

At any rate, determine the validity of the older gas by comparing it with fresh gas. Old gas turns brown so if the old gas looks darker than the fresh gas you have an answer: The gas has started to turn if not turned already. Also, old gas smells more like turpentine than good ole 87 unleaded. Up to you on whether to ring it through your dirt bike's engine but perhaps the better choice finds you eating the cost and dumping the gas or at least using it in your lawn mower. That said, depending on the amount of gas remaining and the size of the fuel container, adding fresh gas might help rejuvenate the old gas enough to burn through it with little problem preventing you from figuring out where to dump the old gas and throw money down the drain.

The short answer to the question is no such time table exists for when gas goes bad but any gas left untouched for a year probably has at best started to turn.

Fuel Stabilizer

Don't think adding fuel stabilizer to the old gas creates a magic potion of fresh gas. It does not work. Add fuel stabilizer to fresh gas with the idea of long term storage. That means either you fill your dirt bike or ATV gas tank with fresh gas then add the stabilizer or add the stabilizer to the leftover can of fresh gas you don't want to lose. Fuel stabilizer slows down the aging process of gas but doesn't last forever. Stabilizer gets you a good year or more out of your stored fuel which easily covers the winter months.

Storing Gas

If you tend to forget, throw caution to the wind or years of experience have taught you that leftover gas from last summer works every time then might we suggest some storage tips to ensure the old gas you plan on using remains in its pure form or at least 98 percent pure. Don't use plastic jugs or cans. Plastic breaks down and allows light through. Hold a plastic can to the light, even a red one; you can see how much gas remains. Instead, use metal. Metal won't contaminate the gas like plastic nor does it allow light in. Leave your metal can filled with gas in a cool, dry and dark place in your garage.

Mechanic's Note: Many riders use plastic containers for hauling gas because of the ease of use and better price point. Granted you regularly burn through the fuel and don't leave gas sitting for an extended period, the plastic jugs or containers work fine.

When using this older gas, pour it through a fuel filter that fits under the gas cap to capture any crud or sediment for good measure.

Use Ethanol Free Gas

Ethanol likes water and ethanol-based gas draws moisture out of the air. The longer you leave ethanol based fuel sitting around the greater chance you end up with not only bad gas but bad gas mixed with water. Your options include:

  • Always using ethanol free gas which eliminates a host of issues but prevents early breakdown of leftover gas
  • Use ethanol-based gas (because you can't find anything else) but from a busy pump station which reduces the chance of moisture contamination
  • Use remaining fresh ethanol-based gas in your car or other gas-powered machine

Dispose of Old Gas

Outside of some performance issues and fouling a spark plug filling your dirt bike with the gas sitting in your garage from last riding season probably won't do much harm. If you'd rather not chance it, use the old gas in your lawn mower and refill with fresh gas for the more sensitive and temperamental engine in your dirt bike or ATV (especially those 2-strokes!). Outside of feeding your lawn mower or power washer, take the old gas to your local auto store or other recycle station that accepts fuel for disposal.

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Written By: AndrewT