How to Winterize a Riding Mower
To winterize a riding mower, add fuel stabilizer and run the engine for 10 minutes to circulate it, change the oil while the engine is warm, clean or replace the air filter, remove the battery and store it indoors on a trickle charger, clean the mower deck, and cover the mower in a dry location.
- Time
- 30 min
- Frequency
- every fall (before last mow)
- Difficulty
- easy
- Cost
- $10
What you'll need
- Oil drain pan
- Socket wrench set
- Battery terminal wrench
- Shop rags
The steps
- 1
Add fuel stabilizer and run the engine for 10 minutes
Pour fuel stabilizer into the gas tank according to the product's dosage instructions. Start the mower and let it run for at least 10 minutes. This ensures treated fuel reaches the carburetor and fuel lines, not just the tank. Stabilized fuel stays fresh through the winter and prevents the varnish buildup that clogs carburetors.
- 2
Change the oil while the engine is warm
Shut off the engine after the 10-minute run. The oil is now warm and drains faster. Locate the drain plug, place a pan underneath, and drain the old oil completely. Replace the oil filter if your mower has one. Refill with fresh oil to the dipstick line. Storing a mower with clean oil prevents acids in old oil from corroding engine internals over winter.
- 3
Clean or replace the air filter
Remove the air filter cover and inspect the filter. Replace paper filters. Wash foam filters with soapy water, let them dry completely, apply a light coat of clean oil, and reinstall. A clean filter is ready to go in spring and prevents you from forgetting this step when you are eager to start mowing.
- 4
Remove the battery and store indoors on a trickle charger
Disconnect the negative terminal first, then the positive. Lift the battery out and bring it inside to a dry, temperature-stable location like a garage or basement. Connect it to a trickle charger or battery maintainer. Cold temperatures drain lead-acid batteries, and a dead battery that sits discharged all winter may not recover.
- 5
Clean the mower deck of grass buildup
Raise the deck to the highest position. Use a putty knife or plastic scraper to remove caked-on grass from the underside of the deck. Grass buildup traps moisture against the metal, causing rust and corrosion over winter. Spray the cleaned deck with a light coat of WD-40 or silicone spray to protect it.
- 6
Cover and store in a dry location
Park the mower in a shed, garage, or under a carport. If outdoor storage is your only option, use a fitted mower cover to keep moisture off. Leave the cover loose enough for air circulation to prevent condensation. Block the wheels so the mower cannot roll.
Why winterizing matters
The single most expensive consequence of skipping winterization is a gummed-up carburetor. Ethanol-blended fuel breaks down in as little as 30 days, and over a 4 to 6 month winter, it leaves a sticky varnish inside the carburetor's tiny passages. The result is a mower that cranks but will not start, or starts but dies under load. Carburetor cleaning at a shop costs $100 to $200. A replacement carb costs $50 to $150 plus labor. A bottle of fuel stabilizer costs $10.
Beyond the carburetor, old oil sitting in the engine all winter contains acids and combustion byproducts that slowly corrode bearings and cylinder walls. A dead battery that freezes while discharged can crack its case and leak acid. Grass buildup on the deck holds moisture against bare metal for months. Every one of these problems is preventable with a 30-minute fall routine.
Fuel stabilizer is the number one step
If you only do one thing, add fuel stabilizer. Pour it into the tank, fill the tank to reduce the air space where condensation forms, and run the engine for at least 10 minutes. Running the engine is critical — stabilizer sitting in the tank does not protect the fuel that is already in the carburetor bowl and fuel lines. The engine needs to pull treated fuel through the entire system.
STA-BIL, Sea Foam, and similar products keep fuel stable for 12 to 24 months. Follow the dosage on the bottle. More is not better — overdosing will not hurt the engine, but it wastes product.
Battery storage
Lead-acid batteries self-discharge over time, and cold accelerates the process. A fully charged battery can survive freezing temperatures. A partially discharged battery cannot — the electrolyte has a higher water content when discharged, and water freezes at a higher temperature than acid. A frozen battery is ruined.
Remove the battery and store it in a location that stays above freezing. Connect it to a trickle charger or float charger that maintains full charge without overcharging. If you do not own a charger, check the battery voltage once a month with a multimeter and recharge it if it drops below 12.4 volts.
Clean the battery terminals with a wire brush or terminal cleaner before storage. Corrosion on the terminals increases resistance and can prevent the charger from maintaining a proper connection.
Deck cleaning prevents rust
Flip the deck height to max and look underneath. Months of mowing leave layers of compacted grass, dirt, and moisture on the underside of the deck. Over winter, that moisture sits against bare metal and causes rust. Heavy rust weakens the deck and creates rough surfaces that grass sticks to even more the following season.
Scrape the deck clean with a putty knife, plastic scraper, or pressure washer. Once clean and dry, spray a thin coat of silicone lubricant or WD-40 on the underside to create a moisture barrier. This also makes the deck easier to clean next season because grass will not stick as aggressively to the slick surface.
Frequently asked questions
- Should I drain the gas or add stabilizer?
- Add stabilizer. Running the tank dry sounds logical, but it leaves residual fuel in the carburetor bowl and fuel lines that will still gum up. Stabilized fuel protects the entire fuel system. The only time draining makes sense is if the fuel is already old and degraded — in that case, drain it, add fresh fuel with stabilizer, and run the engine for 10 minutes.
- What happens if I skip winterizing?
- The most common result is a mower that will not start in spring. Old fuel varnishes the carburetor jets, which costs $100 to $200 to clean or replace at a shop. A dead battery that sat discharged all winter may need replacement ($30-$60). Old oil left in the engine corrodes bearings and cylinder walls. All of this is preventable with 30 minutes in the fall.
- Do I need a trickle charger for the battery?
- A basic trickle charger or battery maintainer costs $15 to $25 and keeps the battery at full charge all winter without overcharging. If you do not have one, at minimum bring the battery indoors where temperatures stay above freezing. A fully charged battery survives cold better than a partially discharged one, but a maintainer is the safest approach.
- When should I winterize — first frost or last mow?
- Winterize after your last mow of the season, which is usually late October to mid-November depending on your climate. Do not wait for the first frost — by then the mower may have been sitting with stale fuel for weeks. Mow, winterize, and store on the same day if possible.
Products you'll need
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STA-BIL Fuel Stabilizer (32oz)
Add to fuel tank before storage to prevent gumming
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