How to Winterize a Lawn Mower: Complete Fall Prep Checklist

How to Winterize a Lawn Mower: Complete Fall Prep Checklist

Winterizing your lawn mower takes 30–45 minutes and prevents the most common spring startup problems — gummed carburetors, corroded fuel systems, and dead batteries. The number one cause of spring no-starts is stale ethanol-blended fuel left in the carburetor over winter. This checklist covers every winterization step for both gas and battery mowers so your equipment is ready to start on the first pull next spring. For a broader overview, see our lawn mower types guide.

What You’ll Need

• Fuel stabilizer (for the stabilize method) or fuel siphon (for the drain method)
• Fresh engine oil (check your manual for correct weight)
• New spark plug (same spec as current)
• Work gloves and safety glasses
• Wire brush and scraper (for deck cleaning)
• Battery tender/trickle charger (for riding mowers and battery mowers)
• WD-40 or light machine oil (for metal surface protection)

Safety Precautions

• Perform all fuel-related work outside or in a well-ventilated area — gasoline vapors are flammable.
• Let the engine cool completely before changing oil or touching the exhaust area.
• Disconnect the spark plug wire before any deck cleaning or blade work.
• Dispose of old gasoline at a local hazardous waste facility — do not pour it down drains or onto the ground.

Step 1: Fuel System — Stabilize or Drain

This is the most important winterization step. Ethanol-blended fuel (E10 gasoline, which is standard at most gas stations) absorbs water over time and degrades into a varnish-like substance that clogs carburetor jets. You have two options:

Option A: Fuel Stabilizer (Recommended for Riding Mowers)

1. Add a fuel stabilizer (STA-BIL, PRI-G, or similar) to a full tank of fresh fuel at the correct ratio (typically 1 oz per 2.5 gallons).
2. Run the mower for 5–10 minutes to distribute the stabilizer through the entire fuel system, including the carburetor.
3. Shut off the mower and store with the full stabilized tank. The stabilizer prevents fuel degradation for up to 24 months.

Option B: Empty the Fuel System (Recommended for Walk-Behind Mowers)

1. Run the mower until it uses all fuel and stops, OR
2. Siphon fuel from the tank using a fuel siphon pump into an approved fuel container.
3. Start the engine and run until it stalls from fuel starvation — this clears remaining fuel from the carburetor float bowl.
4. Turn the fuel shutoff valve (if equipped) to the closed position.

For more on how ethanol affects your fuel system over winter, see our lawn mower ethanol gas problems guide. For correct fuel type and mix ratios, see our lawn mower fuel type guide.

Step 2: Change the Engine Oil

Change the oil at the end of the season rather than the beginning of spring. Old oil contains combustion byproducts and moisture that accelerate internal corrosion during storage. Fresh oil goes in clean and protects the engine through the entire winter storage period.

1. With the engine warm (not hot), disconnect the spark plug wire.
2. Tip the mower to drain oil (for walk-behinds with drain plugs) or use an oil extractor pump through the dipstick tube (easier and cleaner).
3. Reinstall the drain plug and add fresh oil to the correct level — check your manual for oil type (most walk-behind mowers use SAE 30 in warm weather or 10W-30 for year-round use).

See our lawn mower maintenance schedule for complete oil change intervals and viscosity guidance.

Step 3: Replace or Inspect the Spark Plug

Replace the spark plug at the end of every season or every 100 hours of use, whichever comes first. A fresh plug ensures reliable ignition when you start up in spring. Even if the old plug still works, replacing it is inexpensive insurance.

1. Disconnect the spark plug wire.
2. Remove the plug with a spark plug wrench (usually 5/8″ or 13/16″).
3. Note the plug type from the existing plug or your owner’s manual — install the exact replacement.
4. Gap the new plug to the manufacturer’s specification (typically 0.030″–0.035″ for most small engines).
5. Install hand-tight plus 1/4 turn with the wrench — don’t overtighten.

For a detailed walkthrough, see our spark plug replacement guide.

Step 4: Clean and Inspect the Air Filter

A clogged air filter affects spring startup and early-season performance. Clean or replace the air filter at the end of the season:

• Paper filters: Tap gently against a flat surface to remove loose debris. If visibly dirty or damaged, replace — they’re typically $5–10 and not worth trying to wash.
• Foam filters: Wash with warm soapy water, rinse, let dry completely, then re-oil lightly with fresh motor oil before reinstalling.

For a detailed guide, see our lawn mower air filter replacement guide.

Step 5: Clean the Mowing Deck

Grass clippings left on the deck over winter trap moisture and cause rust. Clean the underside of the deck before storage:

1. Disconnect the spark plug wire.
2. Tip the mower on its side (air filter side up) or use a deck wash port if equipped.
3. Scrape compacted grass from the underside with a plastic scraper or stiff brush — metal scrapers can scratch protective deck coatings.
4. Hose down the underside and let dry completely before storage.
5. Once dry, apply a thin coat of WD-40 or a deck spray to the clean underside to inhibit rust.

Step 6: Inspect and Sharpen or Replace the Blade

End-of-season blade inspection is the best time to sharpen or replace — so the mower is ready for the first cut in spring. A dull blade tears grass rather than cutting it, creating brown tips and reducing turf health. See our guide on when to change lawn mower blades for inspection criteria.

Step 7: Battery Care

For riding mowers and battery-powered equipment:

• Riding mowers: Fully charge the battery and connect a battery tender (trickle charger) set to maintenance mode. A battery left uncharged over winter often can’t be recovered. See our riding mower battery guide for battery maintenance details.
• Battery-powered walk-behind mowers: Charge the battery to 40–60% (not full — lithium-ion batteries store best at partial charge) and store in a temperature-controlled environment above freezing. Extreme cold permanently reduces lithium battery capacity.

Step 8: Storage Location

• Store in a covered, dry location — a garage or shed. Outdoor storage under a tarp allows moisture condensation and accelerates corrosion.
• Avoid storing near water heaters or furnaces — pilot light ignition sources near gasoline are a fire risk.
• If storing multiple seasons, prop the mower up on blocks to relieve tire pressure — tires can flat-spot if stationary for more than 6 months.

Winterization Checklist Summary

Frequently Asked Questions

Is it better to drain fuel or add stabilizer for winter storage?

Both work when done correctly. Draining is more reliable for walk-behind mowers because small carburetors have tiny passages that are easy to varnish. Stabilizer is more practical for riding mowers with larger fuel systems where draining is more complex. If you add stabilizer, run the engine for 5–10 minutes afterward to distribute it through the carburetor — otherwise the unstabilized fuel in the carburetor still varnishes.

Do I need to change oil if the mower is only 6 months old?

If the mower is new and the oil has been in for less than 50 hours of use, changing at winter storage is optional but still good practice. Fresh oil in storage is always better than oil that’s sat for 6+ months. The cost of an oil change ($5–8 in oil) is minimal insurance against accelerated internal wear.

Can I skip winterization if my winters are mild?

Even in mild climates, fuel degradation still occurs if the mower sits for 2+ months without use. Ethanol-blended fuel begins to phase-separate in as little as 30 days. If your mower sits any longer than 30 days without being run, stabilizer or fuel system draining is still recommended.

What happens if I skip winterization?

The most common result is a no-start in spring due to a varnished carburetor. Carburetor cleaning or rebuild is typically $40–100 at a service center — much more than the cost of a fuel stabilizer. Skipped oil changes lead to increased bearing wear; skipped battery maintenance leads to permanent battery failure.

Should I store the battery in the house or leave it in the mower?

For riding mower lead-acid batteries, connecting a trickle charger and leaving the battery in the mower works fine in a garage that stays above freezing. If the garage gets below 20°F for extended periods, bringing the battery inside extends its life significantly. Never bring gasoline-powered equipment indoors — only remove the battery.

Conclusion

Winterizing your lawn mower is the single best way to guarantee a trouble-free spring startup. The full process — fuel treatment, oil change, spark plug, air filter, deck cleaning, blade inspection, and battery care — takes less than an hour and prevents the most common and frustrating spring maintenance problems. Do it this fall and your mower will be ready to run on the first pull when grass-cutting season returns.

Related guides:

• How to Store a Lawn Mower
• Lawn Mower Maintenance Schedule
• Lawn Mower Fuel Type Guide
• Lawn Mower Ethanol Gas Problems
• Riding Mower Battery Replacement