How do you winterize a lawn mower for storage?

Winterizing a lawn mower takes about twenty minutes and saves the frustration of a machine that won't start in spring. Stale fuel left in the carburettor over winter is the single biggest cause of spring no-starts, so the fuel is where you start. Everything else, from the oil to the blade, is about putting the mower away clean and ready to run.

Work through it in order:

  1. Deal with the fuel: either run the tank dry, or fill with fresh fuel treated with a stabiliser and run the engine a few minutes so the treated mix reaches the carburettor.
  2. Change the oil while the engine is still warm, so old, acidic oil does not sit in the crankcase all winter.
  3. Disconnect the spark plug wire, then clean clippings and caked grass off the deck underside.
  4. Sharpen and balance the blade so it is ready for the first cut of spring.
  5. Wipe the mower down, and store any battery at a partial charge in a cool, dry place indoors.
  6. Store the mower in a dry place away from children and ignition sources.

Should you run the tank dry or store it with stabilised fuel?

Both methods work; choose one and do it properly. Running the tank dry leaves no fuel to varnish the carburettor, which suits mowers stored for a long off-season, though a little fuel can still linger in the bowl. Storing with stabilised fuel keeps the seals and carburettor wet and protected, which suits shorter storage, provided the stabiliser is mixed into fresh fuel and run through the engine.
  • Run-dry: no fuel left to go stale; best for long winter layups.
  • Stabilised full tank: protects the internals from moisture and rust; best for shorter storage.

What you must never do is leave the mower on untreated pump fuel, because that is exactly what varnishes the carburettor and causes the spring no-start you are trying to avoid.

Why change the oil and sharpen the blade before storage?

Change the oil before storage because used oil holds acids and moisture from combustion that slowly corrode the engine internals over months of standing. Fresh oil in the crankcase over winter means the engine is protected while it sits and ready to run in spring.

Sharpening the blade before storage simply means the mower is ready for the first cut, and it is easier to sharpen an accessible blade at the bench in the off-season than in a hurry in spring. While the blade is off, clean and dry the deck so damp clippings do not rust it over winter. Store any battery pack indoors at a partial charge, never flat and never in a freezing or baking shed.

How do you protect the cylinder for a long layup?

Fogging the cylinder for a long winter layup adds a film of oil that stops the bore and piston rings rusting while the mower stands idle. It is optional for a few months in a dry shed, but worth doing for a damp garage or for storage over a full off-season.
  1. With the engine warm and stopped, disconnect the spark plug wire and remove the plug.
  2. Spray a short burst of fogging oil, or add a teaspoon of clean engine oil, into the plug hole.
  3. Pull the starter cord slowly two or three times to spread the oil around the cylinder.
  4. Refit the plug, but leave the wire off until spring, and note to check the oil before the first start.

Also inflate any pneumatic tyres, and stand the mower off a cold concrete floor on a board where you can, so damp does not wick up into it over the winter.

A worked example of putting a mower away for winter

On the last mow of the season, run the tank low, then top it with fresh stabilised fuel and mow for a few minutes so the treated fuel reaches the carburettor. Back in the shed, change the warm oil, disconnect the plug wire, tip the mower filter-side up, and scrape the deck. Sharpen and balance the blade, refit it, wipe the machine down, and stand it in a dry corner. Bring any battery pack indoors.

Come spring, reconnect the plug, check the oil, and the mower should start within a pull or two. A fuel stabiliser is cheap insurance, and our best lawn mower maintenance picks cover stabilisers, oil, and blades. Dry storage options are in our outdoor tool storage guide, and the wider routine is in our lawn mower maintenance guide. This is general guidance, not a substitute for your mower's manual.