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Classic Car Winter Storage

Since winter is approaching fast, it's time to prepare the weekend drivers for long-term storage. To make a classic car or any car last as long as possible it’s best to only drive it when it's dry and to always park it in a dry garage. When winterising a car, there are a couple of important points to consider in order to avoid a bad surprise when putting it into service again after months of standstill. With the following points, you prepare a car correctly for winter storage making sure it is ready when spring arrives and when temperatures rise again. The winterizing procedure normally takes half a day but it's worth it to protect the car from rusting and long-term idling damage.

Audis UFO Brake Drum
Classic car winter storage

Clean it up

The first thing to prepare a car for longtime storage is to thoroughly clean it up. Dead flies or bird droppings left on the car can damage the paint. Make sure to clean the wheels and undersides of the fenders to get rid of mud, grease or tar. Remove brake dust from the wheels. It is highly aggressive and will eat into aluminium rims. For added protection, give the car a coat of wax. Valet the car from the inside to remove any crumbs or food remaining in order to not attract ants and other bugs.

Car cleaning
Clean the car thoroughly

Garage Preparation

A car should be best parked in a dry and warm garage which is temperature and moisture controlled for long-term storage. The best conditions are dry room temperatures. It is recommended to get a dehumidifier to remove as much moisture from the air as possible. Water and humidity are the enemies of any car. It feeds mildew, mould and accelerates oxidation of metal parts. Upholstery loves to form mould if it's left in wet and damp places. You see this a lot with boats that are stored through the winter. Cushions and upholstery start to become really disgusting when damp. That's why many boat owners remove all the upholstery and bring it home to prevent it from getting mouldy and stinky. You can get air dehumidifiers which feature a granulate to place it inside of the car which keeps the interior dry. But the best is an electric dehumidifier placed in the garage which keeps moisture levels to a minimum.

Bigger surface area of the brake pads with the Inboard brake system
A mouldy car interior is the result of a damp and humid garage

Keep Critters Out

Rodents and bugs love to nest in engine bays. Get a couple of vermin traps/repellents to place around the car. Small animals love dark and hidden spaces such as exhaust pipes, air intakes and other cavities to set up camp. Rodents love to chew on cables, hoses, insulation and other soft materials. Try to cover any gaps where a mouse could enter. Steel wool works well for this. Spray the steel wool with some WD40 so it doesn't start rusting and leave ugly rust stains behind. Spread mothballs or cotton swabs dipped in peppermint oil along the perimeter of the vehicle. The smell will deter mice. You can lay down a few mousetraps and some rat poison too.

car engine keep critters out
Close all gaps and holes with steel wool soaked in WD40

Indoor Cover

When you have the car in a dry and warm garage, cover it with a light cotton blanket to protect it from dust and light. Also, leave the windows half open so the air can circulate inside the car. Only use a cover that is breathable and doesn't trap air or moisture. If you don't have the option to keep your car in a garage, you can get a high-quality cover that is breathable and water-resistant. Don't buy cheap plastic covers from DIY stores. You need a fabric cover that can withstand aggressive UV rays. Plastic covers deteriorate just after three months and get brittle. They will deteriorate quickly and trap moisture underneath.

Indoor Car Cover
Indoor Car Cover

Outdoor Cover

It's best to order a multi-laminate cover that is specifically made to protect cars from the elements. If you live in warm areas, you need to protect the car from heat and the sun. UV rays are extremely aggressive and will damage your clearcoat sooner or later. You can see this frequently with old cars in hot countries. The sun starts to peel off the clear coat. If you live in cold and wet climates, you want to protect the car from moisture, hailstones, snow and ice. Moss starts to grow everywhere in wet climates too. It usually starts at the window seals but quickly spreads all over the car. The moisture also creeps in all the cavities where it promotes rust and oxidation. Get a good, high-quality outdoor car cover that is breathable and has multiple protection layers. It should be specifically made for your climate conditions and cut to your car's shape. Unfortunately, outdoor car covers only last about 3 - 4 years. Even good quality ones will deteriorate after a couple of years because the sun and the elements wear them down eventually. But it's better to sacrifice the cover than live with a rusty and faded car.

Outdoor Car Cover
Outdoor Car Cover

The Battery

It is often recommended to disconnect the battery when storing a car through the winter. This will prevent the battery from being drained by the electronics such as the radio, clock and other consumers. Lead-acid and lithium-ion batteries don't like to be fully discharged because it reduces their life span drastically. If a lead-acid battery is stored over long periods of time at no or a very low charge, sulphate crystal deposits start to form inside of it which reduces the battery's capacity. This process can't be reversed and ultimately destroys the battery. There are many miracle cures out there that promise to reverse the sulphation and remove the crystals. The truth is that they can't be removed again by any household products or electronic devices. Prevention over cure is the key with car batteries. Lithium-ion batteries don't form sulphate crystals but they also don't like to be fully discharged. They will start to leak if fully discharged for long periods of time.

Crystallised and leaking car battery
Left: Crystallised lead-acid battery Right: Leaking li-ion battery in the BMW E30 instrument cluster

When storing or disconnecting a car battery for the winter, make sure it's fully charged. Always disconnect the minus (black) terminal first. You can leave the positive (red) post attached if the battery remains in the car. Disconnecting the negative post will prevent a possible short if the wrench accidentally touches the body of the car. It is not always recommended to remove or disconnect the car's battery for winter storage. For example with the BMW E30, there is a small lithium-ion cell mounted inside the instrument cluster whose purpose is to keep the memory alive. But if the battery gets drained completely, it starts leaking and will ultimately damage the circuit board. If your car has batteries built into its electronics, it's best to hook up a trickle charger. They will monitor the battery and keep it topped up. I recommend the CTEK chargers, which come with different settings for AGM and Lead-Acid batteries.

CTEK Trickle Battery Charger
CTEK Trickle Battery Charger

The Fuel

When you park a car over long periods of time (winterize), you should also top off the fuel tank. If the tank is empty, rust will start developing inside of it since the tank’s walls are bare metal. If you have a Gasoline tank, you probably won’t be able to use it anymore when you bring the car back into service. Gasoline expires after around 3-6 months and becomes unusable. The tank then needs to be drained and filled with new gasoline. But this is still better than replacing the fuel tank due to rust. With Diesel, fuel expiration is not a problem but microbial growth is. When you fill-up the tank with Diesel for winter storage, add a Biocide to prevent the Diesel bug from forming.

Rusty fuel tank
Left: Rusty fuel tank Middle: Diesel Bug Right: Biocide

The Tyres

Tyres are getting damaged when they are sitting for long periods of time on the same spot. The rubber starts to deform temporarily or permanently because the weight of the car is located on one single spot. The tyre gets a flat spot in the area where it was in contact with the ground. This is called "flat spotting" and when driving they will develop a slight ride disturbance or vibration. This usually disappears after a few miles of driving once the tyres have reached their operating temperature and if the car has not been parked for too long. A permanent flat-spotting can occur if the tyres have been standing still under vehicle load for a month or longer. Flat-spotting is intensified by long-standing times, especially in combination with high temperatures and low tyre pressure.

Audi 200
Flat Spotting

It is recommended to at least move the car a bit back or forth once a month to avoid tyre fatigue and deformation. With motorcycles, you would jack up the bike so that the tyres don't touch the ground anymore. You can do the same with a car but this is inconvenient. Moving the car once a month to rotate the tyres by 90 degrees is usually sufficient.

Tyre Rotation
Tyre Rotation

Alternatively, there are flat-spotting protectors available that increase the contact surface with the ground and distribute the load over a bigger tyre area. It is also important to maintain the correct tyre pressure to mitigate flat-spotting. I recommend slightly over-inflate the tyres by 0.2 bar or 3 psi to avoid under-inflation over time since tyres always lose some air.

Flat Spotting Protectors
Left: flat spotting protectors Right: Slightly over-inflate tyres

The Fluids

Keep the coolant system filled and make sure it's still in good shape and has enough antifreeze glycol in it. If temperatures drop below 0 degrees the coolant could freeze and damage the engine. Check the coolant for its antifreeze protection and its galvanic corrosion voltage. Do the same for the brake fluid. Some people recommend draining the coolant but I think that is a bad idea because it could trap moisture inside the system which would start oxidising engine parts. Coolant has antioxidants in it which protect the engine from pitting and corrosion. These additives normally wear down over 2-5 years (depending on what type of coolant) and should be changed after this time. Top up all other fluids such as the windscreen washer fluid and any reservoirs.

Check the cars fluid for storage
Left: Check antifreeze protection Right: Check galvanic corrosion risk

The Brakes

It's usually a good idea to use the parking brake, but don't engage it when leaving the car in storage for an extended time. If the brake pads make contact with the rotors for too long, there is a chance that they might fuse. Unfortunately, there is nothing you can do about the brake disc rotors to start rusting. The rotors are usually made of cast iron which rusts when exposed to air and water. It is a very bad idea to spray them with any kind of lubricant or rust preventer because it will damage the brake pads and it will render the brakes ineffective. The only thing you can do to prevent rusting is to keep the car in a dry environment. In order to prevent rusty rotors, the car would need to be driven at least once a month to brush off surface rust. It's also possible to disassemble the brakes but this requires a lot of time and effort.

Rusty brake disc
Surface rust on brake disc

Change Engine Oil

Engine oils become more and more acidic as they get worn down. Foreign substances such as water, carbon particles, fuel and acids start to build up in the oil and contaminate it over time. Acidic engine oil can damage seals, gaskets and other bare metal engine parts. Before putting the car away in storage, change the engine oil. Warm-up and circulate the oil thoroughly throughout the engine before shutting it down for the season. You can also change the oil filter at the same time which will remove the contaminants and old oil from the filter housing. In spring the new oil is still good and the car is ready to go.

engine oil change
Change engine oil and filter

Spray Bare Metal Surfaces

In order to avoid rust and oxidation, spray or rub all bare metal parts with WD40 but avoid spraying belts, hoses and braking surfaces. WD is not primarily a lubricant but a "water displacement" spray, hence the name WD40. It acts as a rust preventative, penetrant and moisture displacer as well as a lubricant. The manufacturer even promotes spraying WD40 on engine parts on its website. WD40 can also be used to drive moisture away from spark plugs. Use a silicone spray on belts, collars and hoses to prolong their lifetime. The undercarriage should be covered with underbody protection sealant and cavities should be treated with cavity sealing to prevent rusting.

engine bare metal surface
Left: Spray bare metal surfaces with WD40 Right: Seal cavities

Combustion Chambers

Over time the engine oil drains away from cylinder walls, piston rings, and other critical engine components. If the ambient temperature and humidity fluctuate, air vapour can condensate within the combustion chamber and corrosion can develop after 30 days already. The piston and piston rings can get stuck and seize in the cylinders. This is often an issue with engines that are only used seasonally. It leads to seized pistons and the engine won’t crank over anymore. Good prevention to avoid rusty combustion chambers is the application of fogging oil. It is an aerosol petroleum spray for long-term storage and corrosion protection. The oil forms a thin film on metal components that remains intact, unlike WD40 which dissipates over time. It can be used on any 2-stroke or 4-stroke engines. The application of fogging oil is simple and I recommend the following process:

  1. Start the engine and remove the air filter

  2. While the engine is running, spray fogging oil into the air intake of each cylinder

  3. After 10 seconds, shut off the engine

  4. Remove the spark plugs or glow plugs

  5. Deactivate the fuel supply (Pull EFI fuse or press shutoff lever at the injection pump)

  6. Spray fogging oil into each cylinder for 5 - 10 seconds

  7. Turn over the engine by hand or starter motor (Pull EFI fuse or press shutoff lever at the injection pump if you turn over the engine with the starter motor)

  8. Install the spark plugs or glow plugs

Fogging the combustion chambers
Fogging the combustion chambers

You want to keep the combustion chambers sealed off and as dry as possible. Additionally, you can add a desiccant granulate or a sock filled with dry rice into the air filter which will keep the moisture out. Afterwards, seal the air intake with tape to avoid any moisture entering the chambers. The engine will be ready to fire up when spring arrives and pistons won’t be seized in the cylinders. This procedure is not just great for winter storage but many professional garages and classic car restorers use it to store a car and seal an engine over years.

Silica Dry Pack
Left: Dry Pack Right: Sock filled with rice

If you want to learn more about classic car mechanics, consider buying the book: "The Ultimate Classic Car Guide - How to Buy, Maintain and Repair Classic Cars".

Nils Willner

Nils is a Swiss-German engineer who is obsessed with old cars and engines. He is the author of "The Ultimate Classic Car Guide - How to Buy, Maintain & Repair Classic Cars" and the founder of EVC. His passion has always been with old cars and everything with wheels and engines.


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