Can I leave gas in my lawn mower over winter?

There’s an ongoing debate about the correct way to prepare your lawnmower for winter.

Lawnmower Fuel

Some say that emptying the gas tank can cause damage to the engine, others say that the tank should be empty come winter to avoid gas going stale.

The truth is that almost all gasoline now has up to 10% ethanol in it, which can harm the engine’s fuel system.

The worst thing you can do is to leave fuel in an engine for long periods of storage.

Water from condensation combines with ethanol producing a varnish-like substance that creates clogs and corrosion.

At the end of winter, you could be in need of an expensive carburettor cleaning to get your mower running again.

There are two paths you can take to protect your mower over the winter. Either empty the gas tank or add fuel stabilizer and fill up the tank.

Keep in mind that, whichever option you choose, you should always follow the manufacturer’s recommendations and product instructions.

How should I empty the tank?

Just running the engine dry and then storing your mower will not be the correct way to prepare it for winter. First, you need to know what kind of engine your lawnmower has. Either a two-stroke engine or a four-stroke engine.

Two-stroke engine

Run the engine dry or pour the gas from the tank into a container. Then, in a clean gas can mix high-octane gas and oil, in a 50:1 ratio, and a small amount of fuel stabilizer.

Prepare only a few ounces to make the engine run for around four minutes. Close the gas can and shake the mixture for a few seconds. Pour the fuel mix into the mower’s empty gas tank.

You need to start the engine and keep it going until it runs out of fuel and stops. Then pull the chord a few times to make sure that the engine burns off residual fuel.

Now, remove the spark plug from the engine and put a bit of motor oil in the spark plug hole. Lubricate the cylinder by pulling the starter cord to make it spin and reinstall the spark plug.

Four-stroke engine

As with a two-stroke engine, you must empty the gas tank by running the engine or pouring the gas into a container. Then, pour high-octane fuel and a small amount of fuel stabilizer into the tank.

Run the engine for ten minutes and then shut it off. Wait around 20 minutes to let the stabilizer dissolve ethanol residue inside the engine.

Start the engine and let it run out of gas and drain leftover gas in the carburettor’s fuel bowl. Twist the plug open or remove the bowl if it doesn’t have a plug.

What if I don’t want to empty the gas tank?

Maybe you’re concerned that moisture build-up in an empty gas tank will flood it with water during winter. Perhaps you want your mower ready to go come springtime. Or you don’t have anywhere to store fuel other than your mower’s gas tank.

Some people worry that rubber and plastic parts in a fuel system may dehydrate and become brittle if the gas tank is empty. Whatever your situation is, the good news is that you can leave your lawn mower filled with gas over the winter.

You will need to buy fuel stabilizer and fresh fuel, though.

Fuel stabilizer prevents fuel from degrading further, but if you have old fuel in your gas tank, it may already have broken down. Fill your tank 95% full with fresh fuel mixed with fuel stabilizer.

Then, run the engine for a few minutes to ensure that the treated fuel circulates throughout the entire fuel system.  That’s all the process if you don’t want to empty the gas tank. The fuel stabilizer will preserve the fuel for months.

When preparing your mower for winter, there’s much more to it than its fuel system. Regardless of the method you choose, always follow your manufacturer’s recommendations and read product instructions.

If you want your mower to last for decades, perform preventive maintenance during the fall. It doesn’t matter if you have an electric or gas-powered mower, always remove the battery to prolong its lifespan. And tend to all the components of your mower according to the maintenance manual.