Great article from ClassicCars.com: https://news.classiccars.com/store-maintain-car-winter-months/
For the chillier parts of the United States, winter is here and your precious classic car is most likely laid up in the garage until the spring thaw. But storing a vehicle for months requires more than just pulling into its space, turning off the key and shutting the door. Storing and maintaining your car should be a top priority.
There are important preparations and preventive measures to ensure that your classic stays in the same great condition over the winter months, according to Rick Drewry, collector car claims specialist at American Modern Insurance Group. Drewry has more than 30 years experience in the collector car industry and has restored and maintained hundreds of cars and motorcycles.
“One of the main reasons is to protect your investment,” Drewry said. “Cars will deteriorate over time; the goal is to maintain the current condition for as long as possible. Another reason is that it is less work to maintain your car than to fix it, and also cheaper.”
Future reliability is a key consideration, he added and requires proper care of the fuel system, belts, tires, and hoses while keeping dampness to a minimum.
Drewry has Compiled the Following Checklist for Storing and Maintaining Your Car over Winter:
Fuel – Fill up your gas tank and mix fuel stabilizer with the gas. Run or drive the car with the fuel stabilizer until it is up to temperature. This way the stabilized fuel has been distributed throughout your entire fuel system.
Tires – Check the tire pressures. Treat the tires on both the outside and the inside with preservative to prevent the tires from drying out. To avoid flat spots, jack up the car and put it on jack stands.
Paint – Protect your classic vehicle from small scratches by applying a good coat of wax before covering it up.
Interior – Detail the interior so you start off the next season with a clean car. Treat the leather, vinyl, and dashboard.
Battery – Use a battery tender. Even if the battery holds a charge through the winter, you will shorten its life significantly if you do not use a battery tender.
Garage Area – Moisture is your enemy. Make sure the car is stored in a dry environment. A dehumidifier in the garage helps. Also, the heat from a light bulb or the air movement of a very small fan under the car will help reduce the moisture that can build up under the car cover. Always use a breathable car cover to allow moisture to escape.
Dampness and Condensation – If your garage is not heated, you can easily have a dampness issue. Anything metal will heat up and cool down, and when a car warms up after being very cold, it will build up condensation which can cause corrosion. Having a small fan set on low in the corner of the garage will keep the air from settling and will help mitigate corrosion caused by condensation. An incandescent shop light under the engine of a car can help, too.
Animal Infestation – Winter is the time when small animals are looking for places to hide and nest. Having rat or mouse poison or traps positioned in your garage will help. For larger animals (raccoons, squirrels, etc), make sure you address any areas around the garage that could give access to these animals.
Frozen Antifreeze – Poor-quality antifreeze can freeze and crack engine blocks, cylinder heads, radiators, etc. Check your antifreeze to make sure it is strong enough to withstand temperatures dipping down into the single digits or lower. Do not assume the antifreeze is OK without testing it or replacing it with new.
Drewry also has a list of common mistakes made by owners when they store their vehicles:
Inadequate air pressure – Tires that go flat and stay flat over a period of time can end up with damaged side walls. If your car is not up on stands, make sure tire pressure is maintained over the long haul.
The wrong stuff – Do not cover your car with a plastic tarp. All this does is trap moisture, and it is abrasive on exterior paint.
Unclean – Don’t put the car away dirty. Dirt has a tendency to stain over time. Also, putting a cover on a dirty car defeats the purpose and can cause scratches.