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Learning how to winterize a lawn mower takes about an hour, and it’s the difference between a mower that fires up on the first pull in April and one that sputters, smokes, or won’t start at all. Winterizing means getting your mower ready to sit unused for several months: treating or removing the fuel so it doesn’t gum up the engine, changing the oil, cleaning the deck, and storing it where moisture and cold can’t do damage.
This guide will walk you through how to winterize a lawn mower step by step.
Most spring mower problems start with gas left sitting in the tank all winter. This guide covers the full seven-step process for gas push mowers, what’s different for riding mowers and battery-powered mowers, and the common mistakes that turn a simple end-of-season job into a repair bill.
WHAT’S IN THIS GUIDE
- Why You Need to Winterize Your Mower
- When to Winterize a Lawn Mower
- What You’ll Need
- How to Winterize a Lawn Mower in 7 Steps
- Riding Mowers and Battery Mowers
- Common Winterizing Mistakes
- Getting Your Mower Ready in Spring
- Frequently Asked Questions
Why You Need to Winterize Your Mower
Gasoline starts breaking down within about a month. As it ages, it loses the parts that help it ignite and leaves behind a sticky, varnish-like residue. Over a long winter, that residue can clog the tiny passages in the carburetor, which is the most common reason a mower won’t start in spring. Most gas sold today also contains ethanol, which absorbs moisture from the air and speeds up corrosion inside the fuel system.
Old oil is the other problem. Used engine oil carries acids and dirt from a full season of mowing, and leaving it in the engine all winter lets those contaminants sit against metal parts. Grass caked under the deck holds moisture against the steel and rusts it from the inside out. Winterizing handles all three before they cause damage.
When to Winterize a Lawn Mower
Knowing how to winterize a lawn mower helps prevent common engine issues.
Winterize your mower right after your final mow of the season, once the grass has stopped growing. In most of the Midwest and Northeast, that lands somewhere between late October and mid-November. Don’t store your mower early, though. The last couple of mows of the fall are also when you’ll be mulching leaves into the lawn, and our guide on mulching leaves into your lawn covers the mower height and pass count that work best. Winterizing the mower can go on your fall yard cleanup checklist as the last item.
What You’ll Need
You’ll need a fuel stabilizer, a quart of fresh SAE 30 mower oil (or whatever oil your owner’s manual specifies), a new spark plug that matches your engine, and a pair of work gloves to protect your hands from the blade and hot engine parts.
An oil extractor pump makes the oil change much cleaner on mowers without a drain plug, since you can pull the old oil out through the fill tube instead of tipping the whole mower. For the deck and blade, grab a stiff wire brush, a lawn mower blade sharpener, and a socket wrench to remove the blade and spark plug.
How to Winterize a Lawn Mower in 7 Steps
Step 1: Disconnect the spark plug wire
Before you touch the blade or tip the mower, pull the rubber boot off the spark plug and tuck the wire away from the plug. This keeps the engine from accidentally starting while your hands are near the blade. Do this first, every time.
Step 2: Treat the fuel or run the tank dry
You have two good options, so check your owner’s manual to see which one your manufacturer recommends. The first is to add fuel stabilizer. Briggs & Stratton recommends adding stabilizer to your gas can, filling the mower’s tank with the treated fuel, and running the engine for a few minutes so the treated fuel circulates through the whole fuel system. A full tank also leaves less room for moisture to condense inside. Source: Briggs & Stratton — How to Properly Winterize Your Mower
The second option is to run the mower until it’s completely out of gas, so there’s no fuel left to go stale. Either method works. What doesn’t work is leaving untreated gas in the tank all winter.
Step 3: Change the oil
Run the engine for a few minutes first, since warm oil flows out faster and carries more of the dirt with it. Disconnect the spark plug wire again once the engine is off. If your mower has a drain plug, drain the oil into a pan. If it doesn’t, use an oil extractor pump through the fill tube, or tip the mower to drain it out of the fill tube (see Step 4 for which side to tip). Refill with fresh oil to the full mark on the dipstick, and take the old oil to an auto parts store or recycling center.
Step 4: Clean under the deck
Tip the mower on its side with the air filter and carburetor side facing up. Tipping it the other way can let oil and gas run into the air filter and carburetor, which causes smoking and hard starting. With the mower on its side, scrape off caked grass with a putty knife, then scrub the remaining buildup with a wire brush. If you use water, let the deck dry completely before storage so it doesn’t rust.
Step 5: Sharpen or replace the blade
With the mower still tipped, remove the blade bolt and take the blade off. Note which side faces down so it goes back on the same way. Sharpen the cutting edges with a file or blade sharpener, keeping the original angle, and check that the blade is balanced by hanging it on a nail through the center hole. If it’s bent, cracked, or badly worn, replace it instead. Doing this in the fall means your mower is ready to cut cleanly on the first mow of spring.
Step 6: Replace the spark plug and check the air filter
Remove the old spark plug with a spark plug socket and install a new one that matches the part number in your owner’s manual. Spark plugs are cheap, and a fresh one is one of the easiest ways to guarantee an easy spring start. Then check the air filter. Tap out a paper filter or wash a foam one according to the manual’s instructions, and replace it if it’s torn, oily, or clogged.
Step 7: Store it in a dry place
Store the mower in a dry garage or shed, off bare dirt if possible. Leave the spark plug wire disconnected until spring. A lawn mower cover keeps dust, moisture, and critters out over the winter. Avoid storing it next to a furnace, water heater, or anything with a pilot light, since gas fumes from the tank can ignite.
Riding Mowers and Battery Mowers
Riding mowers
Riding mowers follow the same steps for fuel, oil, air filter, and blades, with one addition: the battery. Disconnect the negative cable first, then the positive, and store the battery somewhere cool and dry. A battery that sits connected all winter can drain completely and may not recover. A battery maintainer or trickle charger keeps it topped off until spring. Don’t tip a riding mower to clean the deck. Use the deck wash port if yours has one, or lift the deck according to the owner’s manual. Source: Briggs & Stratton — How to Properly Winterize Your Mower
Battery-powered mowers
Battery mowers are much simpler: no fuel, oil, or spark plug. Clean the deck, sharpen the blade, and store the mower dry. The key step is the battery. Remove it and store it indoors, somewhere that stays above freezing, rather than in a cold garage or shed. Check your manual for the recommended storage charge level, since leaving a lithium battery fully drained or fully charged for months can shorten its life.
Common Winterizing Mistakes
These are the mistakes most likely to leave you with a mower that won’t start in spring:
- Leaving untreated gas in the tank all winter
- Adding fuel stabilizer to the tank but not running the engine afterward, so the treated fuel never reaches the carburetor
- Tipping the mower with the air filter side down, which floods the filter and carburetor with oil and gas
- Working on the blade without disconnecting the spark plug wire
- Storing the mower wet, which lets the deck rust
- Leaving a riding mower battery connected all winter
Getting Your Mower Ready in Spring
If you winterized properly, spring startup takes five minutes. Reconnect the spark plug wire, check the oil level, and fill the tank with fresh gas if you ran it dry. Prime the engine if your mower has a primer bulb, and it should start within a few pulls. If you used stabilizer and your mower starts rough, run it for a few minutes to burn through the treated fuel. Once it’s running, you’re ready for the first mow, and if your lawn needs help after winter, our guide on how to overseed a lawn covers the next step.
Frequently Asked Questions About Winterizing a Lawn Mower
Is it better to drain the gas or use fuel stabilizer?
Both work, and the right answer depends on your mower’s manufacturer. Briggs & Stratton recommends a full tank of stabilized fuel, run through the engine for a few minutes. Some other manufacturers recommend running the tank dry. Check your owner’s manual and follow what it says. The only wrong choice is leaving untreated gas in the tank.
Which way do you tip a lawn mower?
Tip a push mower so the air filter and carburetor face up. On most mowers, that means the spark plug side faces up. Tipping it the other way lets oil and gas run into the air filter and carburetor, which can cause heavy smoke and hard starting.
Can I leave my lawn mower outside in winter?
It’s not recommended. Snow, rain, and freeze-thaw cycles speed up rust on the deck and can let moisture into the engine and fuel system. If you have no garage or shed space, at least use a waterproof mower cover and keep it off the ground.
Do I need to change the oil before storing my mower?
Yes. Used oil contains acids and debris from a full season of mowing, and letting it sit in the engine all winter can damage internal parts. Fresh oil protects the engine while it sits and means your mower is ready to go in spring.
What happens if you don’t winterize a lawn mower?
The most common result is a mower that won’t start in spring because stale gas has gummed up the carburetor. That usually means a carburetor cleaning or replacement. You may also find a rusted deck, a dead battery on a riding mower, or a dull blade that tears the grass on your first mow.