How to Winterize a Lawn Mower: Step-by-Step Guide for 2026
TL;DR
- Winterizing a gas-powered lawn mower takes 45-60 minutes and costs $15-$40 in supplies
- The single biggest mistake is leaving old gas in the tank – it degrades in 30 days and gums up the carburetor by spring
- You need fuel stabilizer or a fuel drain, fresh oil, a new spark plug, and a clean deck before storage
- Do this when nighttime temps consistently drop below 40°F, typically October or November in most U.S. regions
- Skipping winterization is the number one reason mowers fail to start in spring (Briggs & Stratton, 2023)
What You Need Before You Start
Credit: https://hitchesguide.com/
Tools:
- Socket wrench or spark plug wrench
- Oil drain pan
- Wire brush or putty knife
- Garden hose
- Rags or shop towels
Parts and supplies:
- SAE 30 motor oil for most single-cylinder 4-stroke engines (check your manual – some Kawasaki and Kohler engines specify 10W-30)
- Fresh spark plug matched to your engine (NGK or Champion are the standard fits for Honda GCV160 and Briggs & Stratton 675exi)
- Fuel stabilizer such as STA-BIL 360 if you plan to keep gas in the tank
- Fogging oil for long-term cylinder protection (optional but worth it in humid climates)
Safety steps:
- Disconnect the spark plug wire before any blade or deck work – this is not optional
- Let the engine cool completely before draining oil or handling fuel
- Work outdoors or in a well-ventilated space when handling gasoline
Step 1: Run the Mower Low on Fuel or Add Stabilizer
Old gasoline is the number one cause of spring no-starts. Ethanol-blended fuel (the standard E10 at most U.S. pumps) begins to degrade in as little as 30 days and leaves a varnish residue inside the carburetor that clogs the jets over winter.
You have two options. The first is to run the tank as low as possible, then use the choke to run the engine until it dies from fuel starvation – this removes most of the fuel from the carb and bowl. The second is to add a full dose of STA-BIL 360 or Sea Foam to a full tank, run the mower for 5-10 minutes to circulate the stabilizer through the fuel system, then shut it down. Either method works. The worst option is leaving a half-tank of untreated gas sitting for five months.
Step 2: Change the Engine Oil
Credit: https://landscapeunite.com/
Drain the old oil while the engine is still slightly warm – it flows out faster and carries more contaminants with it. Tip the mower toward the drain plug side, remove the plug, and let it drain fully into a pan.
Refill with fresh SAE 30 for most push mowers and walk-behinds running a Briggs & Stratton or Honda engine. Check the dipstick after filling to confirm the level. Used oil contains combustion acids that corrode engine internals if left sitting through winter – a $6 oil change prevents that.
Step 3: Replace the Spark Plug
A spark plug costs $3-$8 and takes five minutes to swap. After a full season of mowing, the electrode gap widens and the tip accumulates carbon deposits. Starting a cold engine in spring on a worn plug is harder than it needs to be.
Remove the old plug with a spark plug wrench, check the gap on the new one against your manual spec (typically 0.030 inches for most Briggs & Stratton and Honda engines), and thread it in by hand first before tightening with the wrench. Do not overtighten – the threads in aluminum heads strip easily.
Step 4: Clean the Cutting Deck
Disconnect the spark plug wire before touching the blade or flipping the mower. Grass clippings compacted under the deck hold moisture against the metal all winter and accelerate rust. Scrape the underside with a putty knife, then rinse with a garden hose and let it dry completely before storage.
While you’re under there, inspect the blade. A blade that is nicked, cracked, or bent should be replaced before spring rather than after – sharpening a damaged blade is not safe. Oregon and Arnold both make direct-fit replacement blades for most Toro, Craftsman, and Husqvarna decks for $15-$25.
Step 5: Check and Clean the Air Filter
A foam pre-filter can be washed with warm soapy water, dried, and lightly oiled before reinstalling. A paper cartridge filter that is grey, crushed, or clogged should be replaced – they run $5-$12 for most standard engines. A clean filter means the engine is ready to breathe on the first pull in spring rather than struggling through six months of accumulated dust.
Step 6: Store the Mower Properly
Store the mower in a dry space – a garage, shed, or covered area. Avoid leaving it on bare concrete for months if possible; a piece of plywood or a rubber mat underneath reduces moisture transfer to the deck. If you live in a humid climate, a light spray of fogging oil into the cylinder (through the spark plug hole, before reinstalling the plug) protects the cylinder walls from rust through winter.
Cover the mower with a breathable cover rather than a plastic tarp. Plastic traps condensation. A fabric mower cover allows air circulation and prevents moisture buildup.
What to Do If Something Goes Wrong
| Problem | Likely Cause | Fix |
|---|---|---|
| Engine won’t drain all fuel | Float bowl still holding gas | Remove the bowl drain screw under the carb and drain separately |
| Oil won’t drain freely | Engine too cold | Warm the engine for 2 minutes first, then drain |
| Spark plug won’t thread in | Cross-threaded on install | Remove, start by hand, go slowly – do not force it |
| Deck rusting after cleaning | Not dried before storage | Sand lightly, apply rust-inhibiting spray paint, store in dry location |
| Blade wobbles on reinstall | Blade adapter worn or bent | Replace the adapter – do not run a wobbling blade |
Frequently Asked Questions
When should you winterize a lawn mower?
Winterize your mower when you are done mowing for the season and nighttime temperatures are consistently dropping below 40°F. In most U.S. regions, that is October or early November. Do not wait until December – by then, any remaining fuel has already started to degrade.
How long does winterizing a lawn mower take?
The full process takes 45-60 minutes for most homeowners doing it for the first time. Once you have done it once, you can move through all six steps in 30-40 minutes.
Do you have to drain the gas or can you just add stabilizer?
Both approaches work if done correctly. Draining is more thorough and the better choice if you are storing the mower for more than four months. Stabilizer is fine for three to four months of storage, provided you run the engine long enough after adding it to circulate it through the carburetor.
What happens if you skip winterizing your lawn mower?
The most common result is a no-start in spring caused by a varnished carburetor from degraded fuel. Cleaning or rebuilding a carburetor costs $50-$100 at a small engine shop (Angi, 2024). The oil and spark plug issues cause slower damage – worn bearings, harder starts, and reduced engine life over multiple seasons.
Can you winterize a lawn mower without changing the oil?
You can, but you should not. Used engine oil contains combustion byproducts and acids that continue corroding internal surfaces during storage. An oil change takes ten minutes and costs less than $10. It is the cheapest insurance you can buy for an engine that might run for 10-15 seasons with basic care.
Quick Recap
- Drain or stabilize the fuel to prevent carburetor varnish
- Change the oil while it is still warm to remove contaminants
- Replace the spark plug for a clean start in spring
- Scrape and rinse the deck, then let it dry fully before storage
- Store in a dry, covered space with a breathable cover – not a plastic tarp
