Winterizing your Classic Car

Last modified: 
06/21/2016 - 22:05

Winterizing your Classic Car
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Cars and trucks are meant to be driven regularly, so when collector vehicles are stored away for the winter months, they are more susceptible to problems. Trapped moisture can lead to mold and mildew in the interior and rust out metal. The corrosive elements of the fluids sitting in your fuel, brake, engine, transmission, and cooling systems for months can also wreak havoc. Because your collector car is likely old, systems may be even more fragile than a conventional daily driven vehicle. This detailed article will guide you through the steps necessary to properly store your classic car through its winter hibernation.

This is the time to detail clean your interior by vacuuming, cleaning out any spilt food (gasp – yes some classic car owners do eat food in their cars), and treating any leather or other delicate materials properly. By removing even the smallest bits of food, you greatly reduce the risk of attracting any rodents that may choose to make your car their home during the winter months. Believe me this does happen, and they will chew up your interior, among other things I will leave to your own imagination.

Closing all air vents is another good idea. In warmer climates, humidity can be a problem which causes mildew and mold. Mildew and mold is extremely damaging to your interior, and to your health. It can be nearly impossible to remove, including the smell. If mildew grows on any fabric or carpet, you will likely need to remove this material. Don’t let this happen to your unrestored beauty.

If you live in a more humid climate or know there's a chance for moisture to get in your vehicle during storage, you can add boxes of baking soda scattered throughout the interior. Taking the tops off tissue boxes or using shoe boxes work well as there is a lot of room and surface area. Baking soda will absorb any small amounts of moisture that may enter the vehicle.

Engine/Transmission/Cooling System:
Oil should be changed regularly, preferably yearly. Gasoline combustion creates byproducts, which combine to create sulfuric acid that condenses on internal engine parts. This is the leading cause of exhaust valve pitting. By changing your oil after it has warmed up by running for a few minutes, you will greatly reduce the engine and valve damage caused by the corrosive chemicals that will sit there all winter. Older cars built before the 1960’s may also not have oil filters at all, or be using a bypass system rather than a pass through system. These designs should definitely be changed yearly to preserve the engine.

Check your transmission fluid and coolant, topping it off or replacing if necessary. Most manufacturers suggest a ratio of 50/50 for antifreeze, but note that some coolant can be premixed and doesn’t require water. Make sure you use distilled water as tap water will leave mineral deposits behind. Flushing your radiator regularly is a good idea, I’m always surprised how much crud is actually in there. While the coolant system is flushed, it makes for a great time to check for any hoses and clamps that should be replaced. Flushing every few years, especially if you don't pile up miles each year, should be adequate.

Wheels, Brakes, and Suspension:
If you don’t ever replace your brake fluid like many collector car owners I know, I’d suggest making a schedule to replace it at least every few years. Glycol based brake fluid (DOT 3, DOT 4, DOT 5) is hygroscopic, which means it can absorb moisture easily which is very damaging to your brake system. Extensive heat from the brakes are already doing a number on the corrosive inhibitors built into the fluid, and water will make the issue worse. Vapor bubbles occur if the fluid boils, which can make the brakes very spongy and can be a hazard on the road. Moisture in the brake lines can easily enter through rubber lines, gaskets, etc.

If you have old brake parts or an old unrestored vehicle, you should make special note to check the moisture content a few times a year. There are test strips and electronic testers available for this, and can lead you to a bigger issue in your braking system if the fluid does not last long.

There is no hard rule on when the fluid should be changed. The testers available only show the moisture content, they do not test the corrosive inhibitive damage. Some owners I know rarely change it, others do it yearly. In a normal scenario I would suggest every 3 years or 5,000 miles, if you are putting on 2,000 to 3,000 miles a year as the average classic car owner drives. Bleeding and replacing the brake fluid could save you time and money down the road when you need to replace major components from damaging corrosion.

If you need to do a major overhaul of your brake system and will be replacing hoses, calipers, etc. you may want to look at converting to a silicone fluid based brake system. Silicone does not absorb moisture like glycol based fluids, and shouldn't need to be changed very often. DO NOT FLUSH your DOT fluid system and add silicone brake fluid, they cannot be mixed. Even the smallest amount of DOT fluid mixing with the silicone fluid will damage the entire system.

When it comes to protecting the wheels, there are 2 main approaches collectors use. The easier option is to over inflate the tires a few lbs (USE CAUTION), so it doesn’t get as flat over the course of storage. This will also help if you are storing the car in a very cold environment. For better protection, I’d suggest lifting the car on jack stands, which removes the strain on the tires and suspension system, and prevents “flat spotting” the tires. This is probably more important if it will be a longer term storage nearing 6 months or more.

Fuel System:
Top off your gasoline tank and add a fuel stabilizer, driving for a few miles before storage so the stabilizer can work through the system. Better yet, equip your car with a gas shut off switch if you don’t have one. While the car is running, turn the switch off until the car dies so the carburetor and fuel lines do not have any gasoline in them. This is the absolute best way to protect the fuel delivery system.

The reason why you should fill the gas tank completely is to prevent condensation on the gas tank walls which can eventually rust out. However, today’s fuels contain ethanol which is good at absorbing moisture. It’s best to use the highest octane rating possible which has less ethanol in it.

Battery and Electrical System:
Batteries will self discharge over time, and I have read this can sometimes happen up to a rate of 1% per day under the right conditions. Not only may you have a problem starting up the car in the spring, but draining the battery can significantly shorten the life of it. Disconnect the battery terminals or remove the battery completely and store in a cool, dry place. Use a trickle charger to keep the battery fully charged during storage, or use a standard low rate charger once a month until it is fully charged.

Running the car so the exhaust system heats up before putting the car into storage will help remove any moisture in the system. Covering the tailpipe will prevent moisture from reentering where it can do serious damage while sitting for months, and keep rodents out.

Clean the exterior in detail and polish if necessary. When you cover your vehicle with a cover, you don't want to drag any dirt or sand over the paint job.

Storage Environment:
Damp garage floors can promote mold and moisture damage from the ground up. Park your car on tar paper or a plastic sheet to prevent moisture building up on the under carriage. Using a proper classic car cover is a must. Read more about selecting the proper car cover to use for your environment at .

Before you put your car cover on, you should tightly close all windows and air vents after the interior and exterior have thoroughly dried from your cleaning. Sealing the car will prevent moisture from getting in. Convertibles should always be stored with the top up to prevent wrinkles, cracks,and creases forming.

For added security, you should consider renting specialty secured storage facilities designed for automotive collectors. These are environmentally controlled buildings which also offer added security to your collector car.


I knew way back in the day, you were supposed to winterize vehicles to prevent the block from cracking due to freezing vehicle fluids, but these days that doesn't seem to be the case. I've ran many of my vehicles with and without winterizing them in the winter and I've had little to no issues. Then again, it's all about how much you care about the cars. I know some of my classic car collecting buddies are seriously into moisture controlled environments and all that jazz. I guess it's all about how far you want to go when winterizing your car.

Sad thing is, I take more caution when searching for a racing rivals hack than I do in winterizing my car. I guess it's all about how much you care about your vehicle.

Not that I don't care about my car - I DO. It's just, I don't think I care enough to go all out in winterizing it during the cold months.

Do you think that by not doing so, I'm causing permanent damage to my vehicles?

That's a good question, as I thought about that after I wrote and published this. I think if you have a vehicle that is not in tip top shape or nothing original, and you just enjoy cruising around a bit in the summer, then you are probably ok skipping some of the winterization steps.

At minimum, I would wash the exterior and use baking soda in the interior in case any moisture gets in or is trapped in the interior. Replacing engine parts and such is a big drag, but mold will completely destroy the interior, and will likely have to be replaced. And that can be a big deal, especially if it is all original.

Secondly, make sure you use fuel stabilizer with a full tank, and let it run for a bit so it gets into the gas lines and engine. You don't want sludgy fuel in your system in the springtime (nor anytime).

I still suggest changing the fluids yearly or 2, but this can also be done in the spring as well, BEFORE it is driven.