Classic car winter storage: the complete professional checklist

Why winter storage should be prepared as a service in its own right

A collector car that stands still for several months does not wear from driving, but it does age: the battery discharges, the tyres deform where they bear the weight, humidity attacks metal and trim, petrol degrades and rodents find an ideal shelter. For a storage professional, winter storage is therefore not mere parking. It is a service that engages the operator’s liability and that the owner must be able to verify.

The safest method is to treat every vehicle with the same checklist at check-in, to record what has been done, and then to follow a care plan throughout the storage period. The recommendations of the manufacturer, the service book or a marque specialist always take precedence over a general rule: a 1960 engine and a recent sports car do not have the same needs.

On arrival: document before you touch

Before any work, carry out a full check-in condition report: photos of every side, the wheels and the interior, mileage, fuel level, existing damage, keys and accessories handed over. This condition report serves as the reference at check-out and protects the owner as much as the operator. Also note the owner’s specific instructions: whether engine starts are wanted or not, products not to be used, contact details of the garage that usually services the car.

The battery: keep it charged

A lead-acid battery that discharges deeply can be permanently damaged. Two options are common:

• A battery maintainer (smart charger with automatic regulation) connected permanently, suited to the battery technology (flooded lead-acid, AGM, gel, lithium);
• Removing or disconnecting the battery, stored in a dry place and recharged periodically, when the vehicle has no electronics sensitive to a power cut.

On recent vehicles, disconnecting the battery can erase settings or trigger alarms; check with the owner or the marque specialist. In every case, measure and record the voltage at regular intervals: it is the best indicator of an emerging problem.

Tyres: avoid flat spots

A tyre that carries the vehicle’s weight at the same spot for months can deform. The usual practices are:

• inflate the tyres to the pressure recommended by the manufacturer, or slightly above for the storage period if the tyre manufacturer allows it, noting the initial pressure;
• move the car a few dozen centimetres at regular intervals to change the contact point;
• use storage cradles or cushions, or place the vehicle on axle stands at the designated jacking points to relieve the tyres and suspension.

Avoid leaving the handbrake applied all winter: the linings can stick to the discs or drums. Chock the wheels and engage a gear if the owner agrees.

Fluids and fuel

Oil and coolant

Used oil contains acidic residues. Many specialists therefore recommend changing the oil before winter storage rather than after. Check that the coolant protects against frost for the temperatures possible in your building, and check the brake fluid, which absorbs moisture over time.

The fuel tank

Two schools coexist: a full tank to limit condensation and oxidation in metal tanks, or an almost empty tank to limit the volume of fuel stored. Adding a fuel stabiliser is common for long storage. The choice depends on the vehicle, the fuel used and the fire safety rules of your building: check them with your insurer and the competent authorities, and always note the level at check-in and check-out.

Humidity, ventilation and cleanliness

Humidity is the main enemy of a stored car: corrosion, mould on leather and soft tops, oxidised electrical contacts. A dry, ventilated room is preferable to a heated but confined one. Measure relative humidity with a hygrometer, record the readings and use a dehumidifier if necessary. Some operators offer ventilated storage bubbles for the most sensitive vehicles.

Wash and dry the car thoroughly before covering it: dirt and droppings retain moisture and can mark the paint. Clean the interior, remove food waste and leave the intended vents partly open.

Cover and rodent protection

Use a breathable indoor cover suited to the shape of the vehicle. A waterproof plastic sheet traps moisture and can damage the lacquer. Never cover a car that is still damp.

Rodents attack wiring looms, insulation and trim. Block the air intakes and the exhaust with visible plugs (and flag them on the steering wheel so they are not forgotten at start-up), regularly check for signs of activity and call in a pest control provider for the building if needed.

To start or not to start: the periodic start-up debate

Running the engine regularly during winter divides specialists. Supporters see it as a way to lubricate the engine, keep the seals working and detect a fault early. Opponents point out that a short start, without reaching full operating temperature, produces condensation in the engine and exhaust without clearing it, and draws on the battery.

The most reasonable position for a professional is not to impose a single rule: agree the policy with each owner and write it into the vehicle’s care plan. If a start is planned, it must allow the engine to reach operating temperature, in a ventilated room, under supervision, and be recorded. If no start is planned, checking the battery and moving the vehicle remain necessary.

Insurance and documents

Check the vehicle’s cover during storage with the owner and their insurer, as well as your own professional liability as custodian. Guarantees, excesses and the conditions for suspending insurance vary between contracts and countries: do not give legal advice, refer to the insurer. Keep a copy of the relevant documents on file (registration certificate, proof of insurance if needed, signed storage contract) and specify the storage location and the contact person.

During winter: a recorded care plan

A care plan lists, for each vehicle, the tasks and their frequency: battery check and charge, tyre pressure, anti-flat-spot rolling, humidity check, dusting, possible engine start. Each task must be dated, assigned to an operator and accompanied by the measurement taken (voltage, pressure, humidity). A periodic report sent to the owner adds value to the service and avoids worried phone calls.

The return-to-road check

Before handing the car back, reverse the preparation: remove the plugs and the cover, return the tyres to their normal pressure, check the fluid levels, the battery, the brakes (the first braking may be less effective if the discs have oxidised), the lights and the absence of rodent traces under the bonnet. Then carry out a check-out condition report compared with the check-in one, signed by the owner or their representative.