How to Winterise Petrol Garden Machinery: Fuel, Oil & Storage Guide (UK)

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How to Winterise Petrol Garden Machinery: Fuel, Oil & Storage Guide (UK)

By Jim Fellows, Garden Machinery Specialist · Updated 23 July 2026 · 10 min read

Every spring, workshops fill with machinery that "broke over winter". Almost none of it broke — it was stored badly, and the winter did what winter does to petrol, water and idle metal. Stale fuel gums carburettors, water freezes and cracks pumps, damp rusts blades and decks, flat batteries lock themselves out, and mice move into air filters. Every one of those is preventable in minutes.

This is the whole-shed checklist. Do it once, on one grey November afternoon, and the troubleshooting guides in this series become articles you read for interest rather than in desperation.

The Whole-Shed Checklist at a Glance

Job 1: The fuel decision — dry or stabilised

Petrol degrades within about a month, and modern E10 also absorbs moisture — untreated fuel left over winter is the single biggest cause of spring no-starts and gummed carburettors. Two valid strategies. Run dry: fuel tap off (or tank drained with a siphon pump), run the engine until it stalls, leaving tank and carb empty — the default for two-strokes, whose mix ages fastest. Stabilise: fill with fresh petrol dosed with fuel stabiliser and run for a minute so treated fuel reaches the carburettor — the better call for generators, which must stay ready to start. Either works; storing untreated fuel is the only wrong answer, and if you did that last year, our carburettor guide awaits. Store spare petrol in a proper sealed container, cool and out of the sun — and start spring with fresh fuel regardless.

Job 2: Change the oil before storage, not after

Used oil carries combustion acids and moisture, and five months of sitting lets them etch bearings from the inside. Four-stroke machines — mower, generator, tiller — go into storage on fresh oil, which is why the autumn timing of the annual service matters: same jobs, better sequence. Fold the plug, filter and blade work into the same afternoon and spring becomes a fuel-and-go.

Job 3: Batteries come indoors

Lithium packs hate a freezing shed and hate being flat even more — a pack stored at zero charge all winter can drop below its protection cut-off and never accept charge again. Every battery in the shed comes indoors at roughly half charge, gets a top-up every month or two, and never winters on the charger or in the tool. Generator starter batteries stay with the machine but live on a trickle maintainer. The full battery-care logic is in our cordless guide.

Job 4: Drain everything that holds water

Frost is the one winter fault that's genuinely terminal. Pressure washers are the classic victim — water freezes inside the pump head and cracks it — so disconnect hoses, pulse the trigger, run the machine two seconds to expel the last of it, and store frost-free (or run pump protector through, which lubricates and antifreezes in one). The same thinking applies to water pumps, hoses, sprayers and the water butt system: drained beats burst. Full frost detail lives in our pressure washer guide.

Job 5: Clean, lubricate, cover — and think like a mouse

Caked grass, sap and mud hold moisture against steel all winter: scrape decks, clean hedge trimmer and chainsaw blades and oil them (the ritual from our blade care guide), wipe bare metal with a light oil, and give cables and pivots a shot of silicone spray. Store everything dry, off the damp floor where possible, under breathable covers rather than sweating plastic sheets. And the veteran's check: mice adore air filter housings and recoil covers as winter homes — a nest of chewed foam in the airbox is a genuine spring classic, so a quick look before first start saves an engine-full of bedding.

The Spring Recommissioning Checklist

Come March: fresh fuel in (correct mix for two-strokes), oil on the dipstick mark, air filter checked for lodgers, batteries charged and seated, tyres and fasteners checked, blades inspected — then start each machine and let it run a few minutes before asking it to work. Machines winterised properly pass this list in ten minutes flat; the checklist exists for the ones that weren't.

Frequently Asked Questions

Should I drain petrol from my mower over winter?

Either drain and run it dry, or store it full of fresh, stabiliser-treated petrol run through to the carburettor. Both prevent the gumming that untreated fuel causes; leaving ordinary petrol sitting untreated is the only losing move.

How long does petrol last in storage?

Around a month before degradation starts affecting small engines — and E10 also absorbs moisture over time. Stabiliser extends storage life considerably; a sealed container, kept cool, helps further. Two-stroke mix ages fastest of all: mix small batches and start each season fresh.

Can I leave batteries in the shed over winter?

Best not. Cold storage and deep discharge both shorten lithium pack life, and a pack left completely flat for months can lock out permanently. Indoors, around half charged, topped up every month or two is the routine that doubles pack lifespan.

Why won't my pressure washer work after winter?

If it leaks from the body or can't hold pressure, water froze inside the pump and cracked it — the most common terminal winter fault in UK sheds. Prevention is draining the machine and storing it frost-free; once cracked, it's a repair-versus-replace calculation.

When should I winterise my garden machinery?

After the last serious use — typically late October to November for mowing kit, after leaf-fall for blowers, and after the final log session for saws and splitters. One combined afternoon covering the whole shed is the efficient way to do it.

Garden Review is reader-supported. As an Amazon Associate we earn from qualifying purchases made through links on this page, at no extra cost to you. This does not influence our advice. Always follow your machines' manuals; store fuel safely in approved containers and dispose of old fuel and oil at approved facilities.