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How to Tell if Your Lawn Mower's Gas has Gone Bad

How to Tell if Your Lawn Mower's Gas Has Gone Bad


Lawn mower gasoline

Whether you've stored your lawn mower away for the offseason or just haven't mowed in a while, you should always take proper steps to get it back into top shape. One of the first things you should do is check the gasoline, especially if the mower doesn't use fuel stabilizer. Gas typically has a shelf life of three months when not treated. Here are a few things to look for when checking the condition of your push or riding mower's fuel.

Common Symptoms of Bad Gasoline

Using bad gas can sometimes present as other problems with your mower. When using expired fuel, these are some key signs:

  • Mower has difficulty starting
  • Lawn mower doesn't start at all
  • Thumping noise coming from the engine

Before you take your mower in for maintenance, check the gasoline, and make sure it's still good. You might only need to put in a fresh tank of gas, which costs less than a trip to the mechanic.

checking mower

What to Look for

Fill mower with fresh gasoline

Do the Smell Test

Gasoline has a very distinctive odor that everyone knows. A simple way to check the status of your gas is with a quick smell. Move your mower outdoors and away from your cars so the gas and oil smells don't confuse your nose. Open the gas cap and waft towards your nose. If the smell is stale or sour, the gas has gone south.

Look at Its Appearance

Fresh gasoline looks much different than spoiled fuel. Gas that is still good will have a clear color and is free of clumping. If you have a push mower, you'll need to get a tin pan or other collection receptacle and empty the tank. Unplug the spark plug and tilt the mower on its side to empty the tank.

Riding mowers typically require a siphon pump to remove the fuel. If the gas that you remove has clumps or is dark in color, then the gas has turned. It's helpful to have fresh gas in a gas can to compare to the gas in question. This way you have a control subject to check against your observations.

Need more help with your mower? Here are some easy mower troubleshooting tips to diagnose the problem.