Winterizing a Gas Mower and Trimmer: Fuel, Oil and Blade Checklist

To put a gas mower and string trimmer away for winter, settle the fuel (treat it with stabilizer or run the engine dry, depending on your manual), change the oil, check the spark plug and air filter, deal with the blade, clean the machine and store it dry. Buy the supplies first, so the job is one afternoon and not three trips to the store. Illinois Extension names stale fuel and gummed carburetors as the most common cause of spring starting problems and a bad spark plug as the second most common, so most of the checklist protects against those.

Buy the Supplies First

Every item below is specific to your machine, so take the manual or the model number with you. The manual is the authority on oil type, plug type and fuel mix.

Step 1: Decide Your Fuel Plan

Fuel is the most debated step, and the sources disagree on method, so read your manual. Briggs & Stratton advises adding stabilizer to the fuel can, filling the tank with treated fuel and running the engine for a few minutes so it circulates. It warns that fuel can degrade in as little as 30 days. University of Illinois Extension says that for 2-cycle and 4-cycle engines, you can drain the gas and run the engine until it stops, which clears fuel from the carburetor, and that 4-cycle engines can alternatively be stored with stabilizer in a full tank of fresh gas.

So there are two valid routes: treated fuel in a full tank, or an empty tank. A 2-cycle string trimmer runs on mixed fuel, so check how its manual wants you to store it. Whichever you choose, do not leave untreated fuel in the machine for months. Store spare fuel in an approved container, away from flame and heat sources, as your manual directs.

Step 2: Oil, Spark Plug and Air Filter

• Oil. Briggs & Stratton says to warm the engine slightly, drain the old oil and refill with fresh oil that meets the manual's specifications. Illinois Extension says changing oil leaves the engine sitting in clean oil, free of contaminants that can damage internal parts. Dispose of used oil as your local rules direct.
• Spark plug. Illinois Extension names a bad plug as the second most common cause of hard starting or no start. Inspect it and clean or replace it, and make sure the plug cap fits correctly. Use the plug type your manual lists.
• Air filter. Briggs & Stratton says to inspect the filter and, if it is dirty, clean it as the maker instructs or replace it.

Do the plug and filter now rather than in spring, so the machine is ready to start on the first mild day.

Step 3: The Blade

Mower blades dull and chip during the season, so winter is the time to sharpen or replace them. Illinois Extension and Briggs & Stratton both recommend checking the blade and sharpening or replacing it. Follow your manual's blade-removal procedure, which will include steps to make sure the engine cannot start, and the manual will also tell you whether and which way to tip the mower, which you should follow exactly.

If you plan to sharpen at home, a file or a dedicated sharpener will do, but check your manual about balancing the blade afterwards, and let a dealer or sharpening shop do it if you are unsure. Our tool sharpeners guide covers files and sharpeners for garden tools; confirm that a tool is suited to mower blades before using it. If you are replacing it, get the part number from the manual or the deck label. Mower blades are not universal.

Step 4: The String Trimmer

A trimmer is simpler. Apply the same fuel decision, inspect the spark plug and air filter, and check the head and shaft for damage. Take off old line and let the head dry. Line can dry out and turn brittle in storage, so many people load a fresh spool in spring. Our trimmer line guide explains how to choose the right diameter and style, and spare line is best kept somewhere cool. If you are weighing a switch from gas, see our electric vs gas trimmers comparison and our guide to cordless trimmers.

Step 5: Clean and Store

1. Clean the machine. Scrape grass off the underside of the deck and wipe the engine. Check the manual before using water around the engine.
2. Lightly oil bare metal. Illinois Extension suggests a light coat of oil on metal surfaces to prevent rust over winter.
3. Battery, if it has one. Briggs & Stratton says to disconnect the negative cable first, then the positive, clean the terminals and store the battery in a cool, dry spot away from heat. Our winter battery storage guide covers cordless packs.
4. Cover and shelter it. Briggs & Stratton says to cover the mower to protect it from dust and moisture, or store it in a shed or garage if you have no cover. Keep the area dry to prevent rust.
5. Write a note. Record what you changed and when, and keep spare parts with the machine.

Related maintenance for hand tools is covered in how to maintain your garden tools.

Spring Restart Notes

When you take the machine out again, check the oil level, look over the spark plug cap and air filter, and confirm the blade is tight, using the manual's steps. If the fuel in the tank or container is old, replace it with fresh fuel as the manual directs, since Briggs & Stratton warns that fuel can degrade in as little as 30 days. Keep the notes you wrote in the fall with the machine. They tell you what you changed, and they make the spring start faster.