How to how do you winterize lawn mowers: A Step-by-Step Guide

Quick Answer / TL;DR: To winterize a lawn mower, stabilize or drain the fuel, change the engine oil, clean or replace the spark plug, and scrape and wash the deck before storing it in a dry, protected space. This prevents fuel gum, internal corrosion, and spring starting failures — and takes under an hour with basic tools.

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What You Need

Having everything ready before you start makes the process smooth and efficient. Here’s the complete list I use in my own shop every fall.

Before you begin: Let the engine cool completely if you’ve just mowed, disconnect the spark plug wire so the mower can’t start accidentally, and work in a well-ventilated area away from any open flames or ignition sources.

Step-by-Step Guide: How to Winterize Lawn Mowers

Step 1: Stabilize or Drain the Fuel System

Prevent the number one cause of spring starting problems: degraded gasoline. Fuel begins breaking down in as little as 30 days, leaving sticky varnish deposits that clog the carburetor and fuel lines. You have two options.

Option A (recommended for most users): Use a fuel stabilizer.

1. Add stabilizer to a nearly full tank. Follow the product’s dosage instructions. A full tank minimizes air space, which reduces condensation inside the tank.
2. Run the engine for 5–10 minutes. This circulates the treated fuel through the entire system, from the tank to the carburetor.
3. Turn off the engine. The mower is now ready for storage with stabilized fuel inside.

Option B: Drain the fuel completely.

1. Siphon the fuel from the tank into an approved fuel-safe container using a siphon pump.
2. Run the engine until it stalls to burn off the remaining fuel in the lines and carburetor bowl.
3. Swirl in a splash of fresh stabilizer-treated fuel, run for a minute to coat internal components, then drain again. This is more involved but the most thorough method.

💡 Pro Tip: Stabilized fuel is only good for about 12 months. If your gas is already a season old, drain it and start fresh — stabilizer can’t revive fuel that has already degraded.

Step 2: Change the Engine Oil

Removing old, acidic oil prevents internal engine corrosion during months of inactivity. Used oil contains combustion byproducts and moisture that can etch metal parts over winter.

1. Run the engine for a few minutes to warm the oil — warm oil drains faster and carries out more contaminants.
2. Locate the oil drain plug (check your owner’s manual) and place a drain pan underneath.
3. Remove the plug and let the oil drain completely, then reinstall the plug securely.
4. Refill with fresh oil to the correct level using a funnel, and replace the filter if your model has one.

⚠️ Warning: Never tilt the mower with the spark plug facing down or the air filter side down — oil can flood the cylinder and air filter. If you must tilt it, tip it with the carburetor and air filter facing upward.

💡 Pro Tip: Pour the used oil into a sealed container and take it to an auto parts store or recycling center — most accept it free.

Step 3: Service the Spark Plug

1. Remove the spark plug with a socket wrench or spark plug wrench.
2. Inspect it: light tan or gray deposits are normal; black, oily, or cracked porcelain means replace it.
3. If it’s in good shape, clean the electrode with a wire brush, gap it to spec (usually 0.020–0.030″), and reinstall finger-tight, then a quarter turn with the wrench.

💡 Pro Tip: Many technicians pour a teaspoon of engine oil into the cylinder through the spark plug hole, then pull the starter rope slowly a few times to coat the cylinder wall before reinstalling the plug. This adds rust protection for storage.

Step 4: Clean the Deck and Undercarriage

1. Scrape the underside of the deck with a putty knife to remove caked-on grass clippings, which hold moisture and promote rust.
2. Hose down the deck and exterior, then scrub stubborn spots with a stiff brush.
3. Let everything dry completely — storing a damp mower invites corrosion.
4. Blow out debris from the engine cooling fins and air filter area with compressed air if available.

Step 5: Store It Properly

1. Choose a dry, protected location — a garage, shed, or basement is ideal. Avoid direct contact with concrete floors if possible; place cardboard or a board underneath.
2. Cover the mower with a breathable mower cover or tarp. Never seal it in plastic, which traps condensation.
3. Remove the battery on electric-start models and store it in a cool, dry place on a trickle charger.

Common Mistakes & Troubleshooting

• Mistake 1: Leaving untreated fuel in the tank all winter. This is the #1 cause of “mower won’t start in spring” repairs I see. The fix is a carburetor cleaning at best, a carb replacement at worst. Prevention: stabilize or drain before the last mow of the season.
• Mistake 2: Skipping the oil change. Acidic used oil slowly corrodes internal bearings and the cylinder wall during storage. If you skipped it, change the oil before the first spring mow — don’t wait for the next scheduled change.
• Mistake 3: Storing the mower on a damp concrete floor uncovered. Moisture wicks into the deck and promotes rust. Fix it by elevating the mower on wood and using a breathable cover.
• Mistake 4: Washing the deck and storing it wet. Trapped moisture under the cover accelerates corrosion on the deck and blade. Always let the mower air-dry fully before covering it.
• Mistake 5: Forgetting the mower won’t start in spring anyway. Before panicking, check the spark plug wire is seated, the fuel is fresh, and the air filter isn’t clogged — these three solve most spring no-start cases without a shop visit.

When to Replace / Gear Consideration

If your mower needed multiple repairs last season, has a rusted-through deck, or the engine smokes and burns oil, winterizing may not be worth it — replacement can be the smarter spend. A fuel stabilizer, fresh oil, and a quality spark plug cost little and often buy you a few more reliable seasons on an otherwise healthy machine.

Frequently Asked Questions

Should I drain the gas or use fuel stabilizer?

For most homeowners, fuel stabilizer in a nearly full tank is easier and just as effective. Draining is the better choice if your fuel is already old, your mower will sit for more than a year, or you’re storing it somewhere with extreme temperature swings.

Can I use regular car oil in my lawn mower?

Yes — most 4-cycle mower engines accept SAE 30 or 10W-30, the same grades used in cars. Always verify the grade and capacity in your owner’s manual, and never use 2-cycle oil in a 4-cycle engine or vice versa.

Is it OK to leave my lawn mower outside all winter?

It’s not recommended. Even under a tarp, outdoor storage exposes the mower to moisture cycles that rust the deck, corrode electrical connections, and degrade the air filter. If you have no other option, use a fully waterproof cover secured against wind and elevate the mower off the ground.

How do I winterize an electric or battery-powered mower?

Electric mowers need no fuel or oil work. Charge the battery to about 50–60%, remove it from the mower, and store it indoors in a cool, dry place (not on a cold concrete floor). Clean the deck and undercarriage, then store the unit dry and covered.

When should I winterize my lawn mower?

After your final mow of the season — typically late October to mid-November in most northern climates, once grass growth has stopped for the year. Winterizing too early means the stabilizer-treated fuel sits unused even longer.

What should I do when I take the mower out in spring?

Check the oil level, inspect the air filter, reconnect the battery if removed, fill with fresh fuel (or confirm the stabilized fuel is under 12 months old), and reconnect the spark plug wire. If it still won’t start after a few pulls, see our troubleshooting list above before hauling it to a shop.