How to Winterize a Lawn Mower Before It Sits All Season

Fuel is the single biggest reason mowers fail to start in spring, so it is worth doing this step properly rather than quickly.

Almost all petrol sold at forecourts now contains ethanol, usually ten percent. Ethanol is hygroscopic, meaning it pulls moisture out of the surrounding air and holds it in suspension. In a car this is harmless because the tank is sealed and the fuel turns over every week. In a vented mower tank sitting through six months of temperature swings, the water separates out and settles at the bottom, which is exactly where the fuel pickup sits.

You have two good options and one bad one.

1. Run the tank completely dry. Let the engine run until it stops on its own, then try to restart it once to clear the carburettor bowl
2. Fill the tank and add stabiliser. Fill to about ninety percent, add the stabiliser at the dose on the bottle, then run the engine for five minutes so treated fuel reaches the carburettor

The bad option is leaving the tank half full, which is what most people do by accident. The air space above the fuel is where the moisture comes from, so a half empty tank is the worst of both approaches.

This catches people out because it feels backwards. Surely you change the oil when you start using the machine again?

Used oil is contaminated with combustion by products and is mildly acidic. Leaving it sitting against bearing surfaces and seals for six months causes corrosion that fresh oil would have prevented. Drain it while the engine is still warm, refill to the mark on the dipstick, and the machine sleeps on clean oil.

Which oil to use is worth getting right rather than guessing, and we have covered the whole question in our guide to choosing the right oil for your small engine.

Grass clippings packed under the deck hold moisture against bare metal for months. That is how decks rust through from the inside while looking perfectly fine from above.

Disconnect the spark plug cap, tip the machine with the air filter facing upward, and scrape the underside back to metal. A putty knife and a stiff brush are enough. Let it dry completely before the machine goes away.

While you are under there, look at the blade. If it needs attention, autumn is a far better time to deal with it than the first sunny Saturday in April.

An engine that sits unused develops surface rust on the cylinder wall, because the oil film drains away over time and leaves bare metal exposed to damp air.

The fix takes two minutes. Remove the spark plug, add roughly a teaspoon of clean engine oil into the plug hole, then pull the starter cord slowly two or three times to spread it around the bore. Fit a new plug while you are there, since spark plugs are cheap and a fresh one removes one variable from spring starting.

This applies to ride on mowers and electric start models. A lead acid battery left in an unheated shed through winter will discharge, and a discharged battery sulphates and loses capacity permanently.

Take it out, bring it somewhere frost free, and put it on a trickle charger or a maintainer. Lithium packs on cordless machines prefer to be stored at around half charge rather than full or empty.

Ventilation beats warmth every time. A cold airy shed is kinder to a machine than a sealed container.

When the season comes round again, the list is short. Refit the battery, check the oil level, confirm the air filter is clean, fill with fresh fuel and start.

If it fires on the second or third pull, the winterising worked. If it does not, the fuel system is the first place to look rather than the engine itself, and most of what can go wrong is fixable at home. We have covered the ones that are not in our guide to the signs your mower needs a professional repair.

The same principles apply to any small engine that spends months idle, including standby power equipment. If you have one, our guide on how to store a generator so it starts when you need it covers the differences that matter.