How often should you winterize a lawn mower?
Updated July 2026
Winterize a gas lawn mower every fall, once, before it sits through the roughly 4 to 6 months of the off-season. The whole job takes about 30 minutes and prevents the single most common spring failure: a carburetor gummed shut by stale fuel. Pump gas today runs up to 10% ethanol, which pulls in water and turns to varnish in weeks, and a carburetor rebuild or replacement runs $75–150 at a shop. Stabilize or drain the fuel, change the oil, and clean the deck, and the mower fires on the first pull in April.
What changes the interval
| Your situation | Interval | Why |
|---|---|---|
| Fuel (the big one) | Stabilize or run dry | Ethanol gas gums the carburetor within weeks and blocks the tiny jets |
| Engine oil | Change every fall | Fresh oil keeps acids and grit out of the engine over winter storage |
| Spark plug | Replace every 1–2 seasons | A $3–8 plug is the difference between a first-pull start and a dead mower |
| Air filter | Clean or replace | A clogged paper filter chokes the engine and washes fuel past the rings |
| Mower deck | Scrape and rinse | Caked wet clippings rust the deck and choke airflow all next season |
| Battery (riding mowers) | Trickle-charge or remove | A lead-acid battery left in the cold self-discharges and sulfates dead |
| Blade | Sharpen or note for spring | Fall is a free chance to pull and sharpen a season-dulled blade |
The cost of skipping it
What skipping it costs: leave ethanol gas in the tank and the odds are high the mower will not start in spring. The varnish plugs the carburetor's jets, and the fix is a $75–150 carburetor clean or rebuild at a shop, often more than a cheap push mower is worth. Old oil left to sit lets acids etch the bearings, and a rusted deck and a dead battery pile on. Against all that, winterizing costs a $5 bottle of stabilizer, a $5–10 quart of oil, and half an hour. Neglect turns a $10 chore into a $150 shop ticket, or a new mower.
How to do it (30 minutes · DIY, basic tools)
- Run the engine, then add fuel stabilizer to a full tank and run it 5–10 minutes so treated fuel reaches the carburetor, or run the tank completely dry instead.
- While the engine is still warm, drain the old oil and refill with fresh oil to the mark on the dipstick.
- Pull the spark plug, check its gap and color, and replace it if it is dark, worn, or more than a season or two old.
- Clean or replace the air filter, and scrape and rinse the caked clippings off the underside of the deck with the plug wire removed first.
- On riding mowers, put the battery on a trickle charger or bring it indoors, and store the mower somewhere dry.
Knowing the interval is the easy half. OnOtto reminds you at the right interval, and it won't let you snooze it into next year. Tasks persist until they're done, and completing mower winterizing schedules the next one automatically.
Put this on autopilot, free for 30 daysFrequently asked questions
Should I run the tank dry or add fuel stabilizer for storage?
Both work; pick one and commit. Adding fuel stabilizer to a full tank and running the engine 5 to 10 minutes keeps the carburetor wet with treated fuel and stops rust in a full tank, the easier route for most owners. Running the tank completely dry leaves nothing to varnish but can dry out gaskets over a long winter. What you should not do is leave untreated pump gas sitting: at up to 10% ethanol, it absorbs water and gums the jets within a couple of months.
Why will my mower not start in spring even after sitting all winter?
Nine times out of ten it is the fuel. Stale, ethanol-blended gas breaks down and leaves a varnish that plugs the carburetor's tiny jets, so the engine cranks but never catches. Before paying a shop $75–150 for a carburetor clean, try the cheap fixes: drain the old gas, add fresh fuel, drop in a new $3–8 spark plug, and clean the air filter. If it still will not fire, the carburetor bowl likely needs pulling and cleaning, which is why draining or stabilizing the fuel in fall is worth the ten minutes.
Do I really need to change the oil before winter instead of spring?
Fall is the better time. Used oil carries combustion acids and moisture that, left to sit for 4 to 6 months, slowly corrode the bearings and cylinder walls. Draining it while the engine is still warm from a final run gets the contaminants out and leaves clean oil protecting the metal all winter. Most walk-behind mowers hold about 15 to 20 ounces and take a $5–10 quart, and many have no filter, so an oil change is a five-minute drain-and-fill. Doing it in fall also clears one chore from the spring rush.