Gas-powered lawn mowers and trimmers take their share of abuse during the warm months, so some lawn mower maintenance at the end of the season—or at the start of spring—is vital to keeping their parts in good working condition. Replacing the oil, spark plugs, and air filters on mowers and applying a bit of elbow grease to grimy recesses, preferably before storing them for the winter, will ensure that they rev up with a pull of the cord next year.
Audrey Meinking, owner of Mineola Bicycle, Fitness, and Mower in Mineola, New York, says the same process also works for other small gas-powered machines such as trimmers and snowblowers. "If you don't take an hour or two for maintenance or bring your machines to a pro for servicing," she says, "there's a big chance you'll be stuck watching the grass grow come spring."
Winterize a Lawn Mower in 7 Steps
Step 1: Empty the gas tank
Unused gas left in a mower over the winter can get stale, gumming up the carburetor and inviting rust.
- First, add fuel stabilizer to the tank, then run the mower to distribute it through the system.
- Turn the mower off and allow the engine to cool, then siphon excess gas into a clean can. (You can put this gas in your car, provided it hasn't been mixed with oil.)
- Restart the mower and run it until it stops; repeat until the engine no longer starts and the fuel lines are empty.
Step 2: Disconnect the spark plug
- Before continuing with the remaining maintenance steps, it's very important that you disconnect the spark plug to prevent the mower from kick-starting accidentally, which could lead to serious injury.
Step 3: Remove the blade
- To make it easier to change the oil and clean the underside of the mower, first detach the blade by unscrewing the bolts that hold it in place. Be sure to wear thick gloves when handling the blade.
- While the blade is off, take advantage of the opportunity to sharpen it (see How to Sharpen Mower Blades).
Step 4: Drain the oil
- If the mower has a 4-cycle engine, you'll need to change the oil. (Some mowers and most trimmers have 2-cycle engines, in which the oil is mixed with the gas.) Have a pan ready, and place a tarp under the mower to catch any oil that might spatter.
- Set the mower on its side with the air filter and carburetor facing up, so oil and residual gas don't spill into them.
- Remove the oil reservoir plug and slowly tilt the mower until the oil begins to drain into the pan.
- Replace the plug when all the oil has drained.
Step 5: Clean the undercarriage
- Use a putty knife and wire brush to scrape off the grass and mud caked on the mower deck. This prevents rust, clears the passageway to the discharge chute, and allows the aerodynamics of the deck to work as designed.
- With the deck cleaned, reattach the sharpened blade.
- Once you've finished and can turn the mower upright, fill the oil tank with fresh SAE 30 or 30-weight oil, and recycle the used oil at a service station. Don't use a thicker oil, such as 10W-40.
Step 6: Change the air filter
A dirty air filter keeps the engine from burning gas efficiently by restricting the air needed for combustion.
- If your mower has a paper filter, replace it with a new one, paper edges facing out. If it's an oil-soaked sponge filter, remove it, wash it out with soap and water, allow it to dry completely, and then add a bit of clean oil to it before putting it back.
- Clear the cooling fins of dirt and debris using a screwdriver or popsicle stick.
Step 7: Replace the spark plug
Remove and replace the spark plug, using a socket wrench with a spark-plug socket, which has a neoprene lining to protect the plug's porcelain casing. Even if the old spark plug is in good shape, for a couple of dollars a new one will perform better and ensure a smooth start come spring.
Step 8: Safely stow any combustibles
Always store gasoline in a detached garage or shed. Use only an approved container, and keep it at least 50 feet from any ignition source. Adding fuel stabilizer will keep it fresh for your generator or snow thrower for up to two years. Lithium-ion batteries lose their charge in the cold, and have been known to catch fire, so remove them from your lawn equipment and store them and their chargers, unplugged, at temperatures above 50 degrees F. Cold doesn’t degrade propane; store it above grade in a well-ventilated area.