Intro
Hey, welcome back to Backyard Engine Pro. The mowing season is winding down and it’s tempting to just roll the mower into the garage and call it done until spring. But those few minutes you skip now have a way of turning into an hour of troubleshooting in April when the grass is already getting out of hand. Cold temperatures, old fuel, and sitting moisture do real damage to engines and fuel systems over a winter storage period.
The good news? Winterizing a lawn mower is simple, takes about 30 minutes, and virtually guarantees a smooth start to next season. Let’s walk through it.
Quick Overview
- Clean the mower thoroughly
- Handle the fuel (stabilize or drain)
- Change the oil
- Remove or maintain the battery
- Check the spark plug
- Store properly
Why Winterizing Matters
A lawn mower that goes into storage without proper preparation is essentially fighting against itself for the next several months. Fuel degrades and leaves varnish deposits in the carburetor. Old oil containing combustion acids corrodes engine internals. Moisture works into the fuel system and causes phase separation in ethanol-blended fuel. Grass and debris left under the deck trap moisture against metal surfaces and accelerate rust.
None of this happens overnight, which is why it’s easy to skip the prep and get away with it a time or two. But eventually the cumulative damage shows up as a carburetor that needs cleaning, an engine that won’t start, or components that have worn faster than they should have.
A few simple steps prevent all of it.
Step 1: Clean the Mower Thoroughly
Before you do anything to the engine or fuel system, get the mower clean. Grass clippings, dirt, and debris left on the mower over winter trap moisture against metal surfaces and actively promote rust and corrosion.
What to do:
- Disconnect the spark plug wire before working under or near the deck
- Tip the mower and scrape all grass clippings and caked debris from under the deck using a putty knife or deck scraper. This is the area that accumulates the most buildup and is the most prone to rust
- Clean the top of the deck, around the engine, and along the frame with a brush or damp cloth
- Clear debris from around the cooling fins on the engine since packed debris there traps heat during the first startup in spring
- Inspect the deck for any rust spots while you have it tipped. Light surface rust can be treated with a rust inhibitor spray before storage
A clean mower going into storage comes out in much better condition in spring.
Step 2: Handle the Fuel
This is the most important winterizing step and the one with the biggest impact on spring startup. You have two solid options and both work well when done correctly.
Option 1: Add Fuel Stabilizer (Easiest)
If you want to keep fuel in the system during storage, this is the right approach.
- Add a quality fuel stabilizer like Sta-Bil to the tank at the dose recommended on the label
- Run the engine for 10 minutes after adding the stabilizer. This circulates the treated fuel through the entire fuel system including the carburetor bowl and fuel lines. Stabilizer sitting only in the tank does not protect the carburetor
- Let the engine cool, then store. The stabilizer will keep the fuel viable for 12 to 24 months and prevent the varnish formation that causes spring carburetor clogs
Option 2: Drain the Fuel Completely (Most Reliable)
If you want maximum protection and don’t mind refueling in spring, draining the system entirely is the most reliable approach.
- Turn the fuel shutoff valve off if your mower has one, or use a hand siphon to remove fuel from the tank
- Run the engine until it stops from fuel starvation. This empties the carburetor bowl and fuel lines of any remaining fuel
- A completely dry fuel system cannot form varnish deposits, cannot suffer phase separation, and cannot corrode from moisture accumulation during storage
Either method works well. The one approach to absolutely avoid is leaving untreated, unstabilized fuel sitting in the system for a full winter.
Step 3: Change the Oil
Changing the oil before winter storage rather than just before spring startup is one of the most impactful habits you can build. Used oil contains combustion byproducts, acids, and metal particles that continue degrading engine surfaces during the months the engine sits. Fresh oil going into storage means clean, protective lubrication from the moment the engine is started again in spring.
What to do:
- Warm the engine up for a few minutes to get the oil flowing freely, then shut it off and let it cool slightly
- Drain the old oil completely, tipping the mower to drain through the fill tube or using the drain plug if equipped
- Refill with the correct oil to the proper level on the dipstick. SAE 30 or 10W-30 as specified in your owner’s manual
- Dispose of the old oil properly at a recycling center or auto parts store
Step 4: Remove or Maintain the Battery
This step applies to riding mowers and walk-behind mowers with electric start systems.
What to do:
- Disconnect the battery from the mower. On most riding mowers this means removing the negative cable first, then the positive
- Store the battery in a cool, dry location away from freezing temperatures. A shelf in an attached garage or basement is ideal. Freezing temperatures can crack battery casings and permanently reduce capacity
- Connect the battery to a trickle charger or battery maintainer during storage. Lead-acid batteries self-discharge at roughly 3 to 5 percent per month, and a battery left fully discharged for months can sulfate and lose its ability to hold a charge permanently
- A $20 battery tender connected to the battery over winter eliminates dead battery problems entirely and is one of the best small investments you can make for electric-start equipment
Step 5: Check the Spark Plug
Winter storage is a natural time to inspect the spark plug and decide whether to replace it now or wait until spring.
What to do:
- Remove the spark plug and inspect the electrode
- If it looks lightly worn or has minor carbon deposits, it’ll likely be fine for one more season. Clean it with a wire brush and reinstall
- If the electrode is visibly worn, heavily fouled, corroded, or the porcelain is cracked, replace it now. Starting spring with a fresh plug means one less variable to chase if the mower is slow to start on the first pull
- Some people prefer to install a fresh plug every fall as a matter of routine, which is a perfectly reasonable approach given how inexpensive they are
Step 6: Store the Mower Properly
Where and how you store the mower during winter matters more than most people realize.
What to do:
- Store indoors whenever possible. A garage or shed protects the mower from freeze-thaw cycles, moisture, and UV exposure that degrade plastics and rubber components over time
- If storing in an unheated space, make sure the temperature doesn’t drop so low that it causes problems for the battery or fuel system
- Cover the mower with a breathable cover to keep dust and debris off while still allowing moisture to escape. A non-breathable plastic tarp can trap moisture against the mower and actually accelerate corrosion
- Store the mower on a flat, level surface. This keeps oil distributed properly in the crankcase and prevents fuel or oil from migrating to places it shouldn’t be
Optional: Replace the Air Filter
If the air filter is heavily soiled from the season’s use, replacing or cleaning it before storage means you’ll start spring with one less thing to address and the engine will be ready to go from the first startup.
What to do:
- Remove and inspect the filter. Tap paper filters clean or replace if heavily soiled
- Wash foam filters with warm soapy water, dry completely, lightly re-oil, and reinstall
- If the filter is brittle, falling apart, or heavily loaded with debris, replace it now with a fresh one ready for spring
Common Mistakes to Avoid
- Leaving untreated fuel in the tank and carburetor for the entire winter, which is the single most common cause of spring starting problems
- Skipping the oil change and storing with old degraded oil in the crankcase, which allows acids and contaminants to continue attacking engine surfaces all winter
- Storing in a damp area or directly on a concrete floor without protection. Concrete draws moisture and transfers it to the mower, accelerating rust on the deck and frame
- Forgetting about the battery and finding it dead and potentially unrecoverable in the spring
Pro Tip
Run the mower for at least 10 minutes after adding fuel stabilizer before shutting it down for storage. A lot of people add stabilizer to the tank and immediately put the mower away, which leaves untreated old fuel sitting in the carburetor while stabilized fuel sits in the tank. The engine run time is what circulates the treated fuel through the carb and lines where it actually does its job. Don’t skip it.
Final Thoughts
Winterizing your lawn mower is a 30-minute investment that pays dividends every spring. Clean the deck, handle the fuel, change the oil, take care of the battery, check the plug, and store it properly. Do those things consistently and you’ll come back every spring to a mower that starts on the first or second pull and runs strong all season.
Now go get that mower put away right. You’ve got this.