How To Tune Up Your Lawn Mower

Regular tune-ups extend the lifespan of your mower and optimize its performance. In this guide, we cover all of the steps needed to maintain and tune up your lawn mower. In the video above, you can see many of these insights and other tips shared by This Old House landscape contractor Roger Cook.

*Unless otherwise noted, costs in this article reflect an average of prices that our team found from hardware stores like Lowes and Home Depot, and on Amazon.com.

Check and Change the Oil of Your Lawn Mower

Routine oil checks and changes prevent engine wear and improve lawn mower performance.

To check the oil level of your lawn mower:

1. Position the mower on level ground for an accurate reading.
2. Locate and remove the dipstick, which is usually found near the engine.
3. Clean the dipstick with a rag to clear any old oil residue.
4. Fully reinsert the dipstick. Then, remove it again to check the current oil level.

If the oil doesn’t need to be changed but the oil level is below the “full” line on the dipstick, you can add new oil. Go slowly so you don’t overfill the tank. 

You should change the oil if it appears dirty or darker than usual. If you’re not sure how to tell, Cook compares new oil and dirty oil in the video. You can change it by following these steps:

1. Gently tip the mower onto its side. Make sure the air filter is facing upward to prevent contamination.
2. Drain the used oil into a container with a secure lid.
3. Safely recycle the old oil at designated centers, including service stations or auto shops.
4. Pour in new oil gradually, monitoring the levels with the dipstick to avoid overfilling.

Pro Tip: Roger Cook, This Old House landscape contractor, advises checking oil while the engine is cold: “When the engine’s cold, all the oil is drained down. You’re getting a proper reading. If you check it when it’s hot, some of that oil could still be up in the engine. You could actually overfill the oil.” He adds that the worst scenario is running an engine with low oil: “You could actually seize the engine, blow it up.”

Replace the Lawn Mower Air Filter

The air filter should be replaced at least annually or more frequently in dusty environments. Check it regularly, and if it appears dirty or clogged, it needs to be changed:

1. Locate the air filter housing. It’s typically found on the side of the mower’s engine.
2. Remove the cover to access the old filter.
3. Clean the housing to eliminate any trapped debris or dust.
4. Insert the new filter, making sure it fits snugly within the housing.
5. Re-secure the cover to protect the new filter.

Not all air filters are the same. According to This Old House Magazine, if your mower has a paper filter, replace it with a new one with the 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. Also, clear the cooling fins of dirt and debris using a screwdriver or Popsicle stick.

Pro Tip: When troubleshooting a mower that won’t start, Lee, a small-engine repair expert featured on This Old House, recommends checking the air filter first: “The engine has to breathe,” he explains. A brand-new filter should look clean and white—after a season or two, “it’s gonna be gray, it’s gonna be dirt.” His advice: “Just blow it out, you could, if you want it, or you could just get a new one.”

Change the Lawn Mower Spark Plug

Manufacturers recommend replacing a lawn mower’s spark plug every 25 to 50 hours of use, at the beginning of each season, or when you notice engine trouble, whichever comes first. 

1. For safety, disconnect the spark plug wire to prevent unintended ignition.
2. Unscrew the old plug using a deep socket wrench.
3. Check and adjust the gap on the new plug according to the manufacturer’s instructions.
4. Begin threading the new plug by hand to avoid cross-threading.
5. Securely tighten it using the wrench, making sure not to over-tighten.
6. Reconnect the spark plug wire.

Sharpen the Lawn Mower Blade

A sharp blade is needed for a clean cut and a healthy lawn. Dull blades can tear grass, which can lead to browning and make the grass prone to disease.

To sharpen the blade: 

1. Disconnect the spark plug wire to prevent accidental starting.
2. Tilt the mower with the air filter facing upward to access the blade.
3. Use a wrench to remove the blade from the mower.
4. Sharpen the blade on each end with a metal file or grinder, following the original bevel angle for consistency.
5. Balance the blade using a balancer; an unbalanced blade can strain the engine.
6. If needed, file the heavier side to achieve balance before reinstalling the blade on the mower.

Pro Tip: This Old House landscape contractor Roger Cook advises: “You let the lawn tell you when to sharpen. You take a piece of grass after you cut it and you look at it. If it’s a nice clean cut on the top of a piece of grass, then your blade is great. If it’s all ragged on the edge, that’s not good.” A ragged cut can invite disease and give your lawn a brown cast two or three days after mowing.

Use Fresh Gasoline in Your Lawn Mower

Most types of gasoline use ethanol, which can damage a lawn mower’s engine over time. You should only purchase the amount of gas you’ll need within a month to prevent it from going stale. Fuel additives can help to extend the life of gasoline; you should add a fuel stabilizer if you’re not planning to use the mower in the next 30 days. If possible, purchase ethanol-free gas.

If you’re storing the mower for an extended period, run the engine dry or empty the fuel tank.

Pro Tip: Craig Murray, owner of Liffco Power Equipment in Mineola, N.Y., advises: “Don’t leave cans of gasoline sitting around, because the fuel will absorb water, which makes motors run rough. Funnel whatever’s left into your car’s tank, then buy fresh gas come springtime.”

Additional Lawn Mower Tune-Up Tips

In addition to these five tasks, there are several other maintenance practices to keep your mower in top condition:

• Regularly clean the mower deck to prevent grass and debris buildup.
• Check and tighten all bolts and screws to avoid any loose components.
• Lubricate moving parts as per the manufacturer’s guide.
• For riding mowers, check the tire pressure regularly for even cutting and fuel efficiency.
• Store the mower in a dry area protected from the elements to prevent rust and deterioration.

Our Conclusion

To keep your lawn mower in top shape, it’s important to perform these tune-up tasks regularly. Staying on top of the maintenance can help you avoid costly repairs or the need to purchase a new mower earlier than expected.

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