How to Winterize a Lawn Mower

The number one reason a mower won’t start in spring is fuel that was left to rot over winter. Modern gasoline—especially the ethanol blends sold at most pumps—breaks down in as little as 30 days, gumming up the carburetor and clogging tiny fuel passages. A proper winterizing routine takes under an hour and saves you a frustrating no-start, a carburetor cleaning, or a trip to the repair shop come April. This guide walks through the full off-season service step by step: handling the fuel, changing the oil, dealing with the spark plug and battery, sharpening the blade, cleaning the deck, and storing the machine so it fires up on the first pull next year.

Before You Start: Safety and Supplies

Work outdoors or in a well-ventilated area, and let the engine cool fully before touching it. Disconnect the spark plug wire first so the engine cannot accidentally start while your hands are near the blade—this is non-negotiable. Gather what you’ll need: fresh engine oil (check the manual for type and capacity), an oil-drain pan, a new spark plug, an air filter, fuel stabilizer, a socket or wrench set, a blade-sharpening file or grinder, work gloves, and shop rags. Most of this is a single inexpensive trip to the hardware store, and many of the parts are due for replacement anyway.

Step 1: Handle the Fuel

This is the most important step. You have two valid approaches—pick one.

Option A: Stabilize the fuel

1. Add a fuel stabilizer to the tank at the dose printed on the bottle (typically about one ounce per 2.5 gallons).
2. Top off the tank with fresh gas. A full tank leaves little air space for condensation to form.
3. Run the engine for 5 to 10 minutes so the treated fuel circulates through the entire fuel system and into the carburetor.

A quality fuel stabilizer keeps gas usable for up to a year or more, which is ideal if your mower has a sealed system or you’d rather not drain it.

Option B: Drain the fuel completely

1. Siphon the gas from the tank into an approved container, or run the mower until it sputters out.
2. Restart and let it run until it dies again to burn off fuel left in the carburetor bowl—dry is the goal.
3. If your carburetor has a drain screw, open it to empty the float bowl completely.

Draining is the surest protection against ethanol gumming. Either approach works; the cardinal sin is leaving untreated gas sitting in the system for months.

Step 2: Change the Oil

Used oil carries combustion acids and moisture that corrode internal parts if left to sit all winter. Changing it now—rather than in spring—means clean oil protects the engine through storage. Warm the engine briefly so the oil flows freely, then shut off and disconnect the spark plug. Drain the old oil into a pan via the drain plug, or tip the mower (carb and air-filter side up) and drain through the fill spout on small push mowers. Refill with fresh oil of the grade your manual specifies—commonly SAE 30 or a 10W-30 for varying temperatures—to the correct level on the dipstick. Take the used oil to an auto-parts store or recycling center; never pour it on the ground or in the trash.

Step 3: Spark Plug and Cylinder

With the plug wire already off, remove the spark plug and inspect it. A plug that’s heavily fouled, worn, or has a cracked insulator should simply be replaced—they’re cheap. To protect the cylinder over winter, pour about a teaspoon of fresh engine oil into the spark-plug hole, then slowly pull the starter cord two or three times to coat the cylinder wall and piston with a protective film (this is called fogging). Reinstall the spark plug, but leave the plug wire disconnected until you’re ready to use the mower in spring. This simple step prevents internal rust on engines that sit idle for months.

Step 4: Air Filter

A clogged air filter chokes the engine and makes it run rich. The off-season is the perfect time to deal with it. Replace a paper filter if it’s dirty—they’re inexpensive and you’ll be ready for spring. If your mower uses a foam filter, wash it in warm soapy water, let it dry completely, and work a little clean engine oil into it before reinstalling. Starting the season with a fresh filter means better fuel economy and a cleaner-running engine.

Step 5: Sharpen and Balance the Blade

A dull blade tears grass instead of cutting it, leaving a ragged, browned lawn that’s more prone to disease. Doing this now means you’re ready to mow the moment spring arrives. With the spark plug wire still off, tip the mower (carb side up), wedge a block of wood against the blade to stop it turning, and remove the blade bolt. Mark the blade’s orientation so you reinstall it the same way.

1. File or grind the cutting edge to restore a sharp bevel, following the existing angle—roughly 30 to 45 degrees. You don’t need a razor edge; a “butter-knife” sharpness cuts grass cleanly.
2. Sharpen both ends equally to keep the blade balanced.
3. Check balance by hanging the blade on a nail through the center hole—if one side dips, grind a little more off that heavier end until it hangs level.
4. Reinstall the blade in its original orientation (the lift wings face up toward the deck) and torque the bolt firmly.

If the blade is bent, deeply nicked, or worn thin, replace it—an unbalanced blade vibrates and can damage the crankshaft. A good blade sharpening kit makes this a five-minute job.

Step 6: Clean the Deck and Body

Caked grass clippings under the deck trap moisture and breed rust, and they restrict airflow that the mower needs to discharge clippings cleanly. With the blade off (or wire disconnected), scrape the underside of the deck with a putty knife and stiff brush until the metal is clear. Wipe it down, let it dry fully, and if the deck has bare or rusty spots, a light coat of paint or a spray of silicone protectant helps prevent corrosion over the damp winter months. Clean the top of the machine too, clearing debris from the engine’s cooling fins so it doesn’t overheat next season.

Step 7: Battery Care (Riding and Electric-Start Mowers)

If your mower has a battery, cold and disuse will drain and damage it. On a riding mower, disconnect the battery (negative terminal first) and store it in a cool, dry place off bare concrete, or leave it connected to a maintainer/trickle charger that keeps it topped up without overcharging. Clean any corrosion off the terminals with a baking-soda-and-water paste and a wire brush. For battery-powered electric mowers, charge the lithium battery to roughly half capacity, remove it from the tool, and store it indoors at room temperature—extreme cold shortens lithium battery life and storing at full or empty charge degrades it.

Step 8: Store It Right

Put the mower somewhere dry and protected—a garage, shed, or basement. Avoid storing it directly on bare concrete, which wicks moisture upward; set it on a wood pallet, scrap plywood, or a rubber mat. Cover it with a breathable mower cover or tarp to keep dust and rodents off, but don’t seal it in airtight plastic that traps condensation. Keep it away from any appliance with a pilot light or open flame if there’s any fuel left aboard. Stored this way, your mower will start easily and cut cleanly the first time you need it in spring.

With the mower handled, the off-season is also a good time to plan next year’s lawn care—our guide to the right lawn watering schedule pairs well with a freshly serviced machine, and you’ll find more seasonal maintenance how-tos on the Outdoor Living hub.