How to store a classic or supercar over winter

The short version

• Air. Dry and steady. Condensation is the enemy, and it forms when the temperature swings.
• Battery. A conditioner on all winter, matched to the battery type. Lithium needs a lithium charger or mode.
• Fuel. Follow the handbook. For older cars, avoid leaving E10 in the system over winter.
• Tyres. Set the pressure the maker gives, then take the weight off on stands or move the car each month.
• Brakes. Put the car away dry, handbrake off, wheels chocked, on private land.
• Cover. Breathable, never plastic sheeting.
• Paperwork. SORN if it stays off the road, and keep fire and theft cover in place.

The printable checklist below turns all of this into three short lists: before, monthly and spring.

Humidity: the number that matters most

Moisture is described as arguably the biggest killer of stored classic cars by a storage specialist quoted in a classic car insurer's winter guide. Metal, leather, fuel and oils all degrade with long exposure to damp air.

The same guide's dehumidifier specialist suggests bringing relative humidity down to around 55%, with a unit that extracts about 20 litres a day. Treat that as a ceiling to stay under, not a target to swing around.

Stability matters as much as the level. Mild days followed by cold nights push the air past its dew point, and water condenses on the car. That is worst in autumn and spring.

The AA suggests sealing the garage and running a dehumidifier instead of ventilating it. It warns that a dehumidifier needs a low-temperature cut-out, because dehumidifiers cannot work below about 4C. If you suspect damp, lift or remove the carpets and dry them thoroughly.

Museums measure rather than guess. The Haynes Motor Museum checks relative humidity, light levels and pest traps every month. A cheap hygrometer in the garage lets you do the same.

Temperature

Cold itself is not the main problem. The AA notes that corrosion is not a concern in very cold weather, provided the car is dry and free of road salt. Swings are the problem, because each swing can bring condensation.

So aim for steady, not warm. Insulate the garage, stop the draughts and keep the door shut. If you can, put the car away after a dry drive, while it is still warm, so it goes into storage free of water.

The battery: lead-acid and lithium are not the same

A battery left alone runs down. Even a disconnected one self-discharges, and a modern car's electronics draw current all the time. OptiMate gives an example: a typical 10 milliamp draw costs 1.7 amp hours every seven days.

The RAC says to check that your charger suits your battery type, and whether it can be left connected indefinitely. Charge in a dry, well-ventilated space, because charging can release a flammable gas. On modern cars, use the connection points the handbook specifies. Connecting to the battery negative can bypass the battery management sensor.

Lithium batteries

Lead-acid and lithium batteries need different maintenance charging in storage, OptiMate says. A lithium starter battery usually has less capacity than the lead-acid one it replaces, so standing drain empties it sooner. Use a charger with a lithium mode, or a dedicated lithium charger. Never assume an old lead-acid conditioner is safe on lithium.

Follow the maker

Some makers are explicit. Ferrari's LaFerrari Owner's Manual and Warranty Booklet say the car must be connected to its battery conditioner at all times when not in use. Ferrari's bulletin tells owners to use the conditioner supplied with the car.

Porsche's published storage instructions for the electric Taycan say its 12 volt battery is kept charged from the traction battery. Owners are told to leave the car connected to its AC charging equipment, not a separate maintainer.

If your car came with a conditioner, use that one. If the handbook names a charging point or a mode, follow it.

Fuel: full tank, empty tank, or stabiliser?

This is where the advice genuinely splits.

• The AA says that unless you can guarantee a dry, stable environment, store the car with a full tank, to leave less space for water to condense.
• The RAC says that for long storage you should either drain the tank or use a fuel stabiliser.
• A restoration specialist quoted in an insurer's winter guide says he has yet to find a stabiliser that works. He stores cars with very little fuel and adds fresh fuel in spring.

For older cars, ethanol settles the question. The FBHVC warns that storing petrol with ethanol over a winter can corrode historic fuel systems. For a long lay-up it recommends replacing E10 with ethanol-free petrol. It also says not to leave fuel systems dry, because seals and gaskets shrink and crack.

E10 has been the standard petrol in Great Britain since September 2021. The government says some classic, cherished and older vehicles are not compatible. If your car is not listed as compatible, it advises using E5 super grade. The FBHVC recommends Super E5 for all vehicles built before 2000.

Our reading: for a modern supercar, follow the handbook. For a classic, avoid ethanol over winter and never leave the system dry.

Tyres: flat spots, pressure and stands

A tyre that stands in one place for months can develop a flat spot. Most recover once warm, but not all.

On pressure, the sources disagree. The RAC, and a tyre specialist quoted in an insurer's guide, say inflate to the maximum recommended pressure before storage. Michelin says the opposite: keep tyres at placard pressure, not higher, because over-inflation can make flat spots worse. Porsche's Taycan storage instructions give a specific storage pressure of 3.5 to 4.0 bar.

The way through is simple. Use the figure your car's maker gives for storage. If it gives none, use the normal placard pressure, and reset it before the first drive.

Taking the weight off avoids the argument. The AA suggests raising the car on blocks or stands so the wheels clear the ground. The US National Park Service, writing for museum collections, puts stands under the suspension and says the suspension will not be fatigued by it. Michelin says it has no data to show tyre cradles help.

If the car stays on its wheels, roll it a short way every month so the tyres rest on a new patch. Check the date code too. Michelin UK and specialist suppliers advise replacing tyres at ten years old, whatever the tread looks like.

Brakes and the handbrake

A handbrake left on all winter can seize, the AA warns. Its advice is to leave it off only on private land, with the wheels securely chocked.

Wet brakes make it worse. Putting a car away wet with the handbrake on can etch a pad-shaped patch of corrosion into the disc. Dry the brakes with a short drive first.

Cars with an electric parking brake follow the same logic. Porsche's Taycan instructions say to select Park, switch the electric parking brake off and block the wheels.

Oil and fluids

For storage beyond three months, the AA advises checking the oil and arranging an oil and filter service. A lubricant specialist quoted in an insurer's guide says it matters less whether the change comes before or after storage, as long as it is not skipped.

The AA also suggests slackening auxiliary drive belts, such as the alternator and air conditioning belts, but never the camshaft drive belt. Lift the wiper arms so the blades do not rest on the glass. Check every fluid level again before the first start in spring.

Pests

A car left for months can attract rodents and insects, the RAC notes. One owner's published account describes mice chewing through a fuel line and a wiring loom.

The National Park Service's museum guidance suggests keeping the doors closed, sealing the air intake, and placing a sticky trap under a seat to show whether anything has got in. Set traps around the car too, and check them monthly, as museum conservators do.

If you block the intake or the exhaust, write it down. The AA advises leaving a note in the car of everything you have done to it, so nothing is missed in spring.

Covers: breathable, never plastic

A cover keeps dust off, but it must let moisture out. The National Park Service specifies a breathable, water-resistant cover for stored vehicles. Published insurer guidance also calls for breathable covers, against dust, moisture and pests.

That rules out plastic sheeting. It traps the very damp the cover is meant to keep away, and holds it against the paint. Use an indoor cover indoors, fitted to the car, and clean and wax the car before it goes on.

Security

A car that sits for months is a known target. Secured by Design, the police crime prevention initiative, says relay theft of a keyless car can take as little as 60 seconds.

• Keep keys in a signal-blocking pouch, or in a key safe or locked cabinet.
• Fit a steering lock or wheel clamp as a visible deterrent.
• Keep any tracker subscription up to date over the winter.
• Alarm the garage, and fit secure garage doors.
• Cover any garage windows so the cars cannot be seen from outside.

Our car gallery security guide sets out how a private collection is protected in layers.

Insurance and the law while laid up

These notes are general. Check your own policy and tell your insurer before you change anything.

• SORN. If the car stays off the road, you can tell the DVLA with a Statutory Off Road Notification, for example when it is kept in a garage. You get a refund of any full months of tax left. You cannot use the car on the road until you tax it again.
• Insurance. Continuous insurance enforcement means a car declared SORN and kept off the road does not legally need insuring. That is not the same as being safe to leave uninsured. Fire and theft risks remain. The AA notes you may be able to reduce cover to fire and theft only.
• Where the car is kept. Published insurer guidance asks owners to check that the policy covers the car at a storage facility away from home, and to keep the valuation up to date, ideally on agreed value terms.
• MOT. If the MOT lapses over winter, you can only drive the car to a pre-booked MOT or a repair.
• Historic vehicles. A car built or first registered more than 40 years ago, without substantial changes, does not need an MOT. It must still be kept roadworthy.

Should you start the engine during storage?

Only if you will run it properly. The RAC says to avoid starting an engine only to switch it off again shortly after. A lubricant specialist quoted in an insurer's guide agrees: if you start it, warm the engine and ideally the whole car through thoroughly. Most wear happens at start-up, and a full warm-up drives water vapour out of the engine.

Never run an engine in a closed garage, because the exhaust fumes are toxic, as Goodwood's own lay-up advice warns. If the car cannot be driven and fully warmed, leave it still and keep the battery on a conditioner.

A monthly routine

The Haynes Motor Museum checks pest traps, humidity and light every month, and the condition of every vehicle once a year. A private garage can follow the same rhythm.

1. Read the hygrometer and empty or check the dehumidifier.
2. Check the conditioner is on and showing a healthy charge.
3. Look under the car for drips, and under the bonnet for nests or chewing.
4. Check the traps.
5. Check tyre pressures, or roll the car a short way if it is on its wheels.
6. Lift the cover and look at the paint, the leather and the glass for damp or mould.

Waking the car in spring

The AA's order works well.

1. Check the MOT and tax are current. Taxing the car cancels the SORN.
2. Read your own note. Remove any intake or exhaust blocks, and refit the wiper arms.
3. Check nothing is nesting under the bonnet and no pipes or hoses are chewed.
4. Set the tyres back to road pressure.
5. Check all fluid levels before starting the engine.
6. Check the brakes, including the handbrake, which may have seized.
7. Drive gently, and use the brakes over the first few miles to clean off surface corrosion.
8. After a long lay-up, book a full service.

When a garage is not enough

Everything above is a workaround for a room that was never built for a car. A dehumidifier fights the weather, a conditioner fights the drain, and you check both by hand.

A collection that matters, or a car that cannot be replaced, deserves a space designed for it. A BELOW gallery holds humidity in a steady band all year, keeps the power on through a cut, and reports every reading to your phone. Our air and climate guide explains how the air is managed, and our car vault guide explains what a secure, climate-controlled vault needs.