How to Winterize Your Vehicle: The 7 Checks to Make Before the First Hard Freeze

Knowing how to winterize your vehicle is mostly knowing which handful of things actually change when it gets cold, and checking those before the weather forces the issue. It is not a long list and it is not expensive. It is just time sensitive, because every item on it gets harder to deal with once there is ice on the driveway.

The Federal Highway Administration puts the scale of winter driving in perspective. Averaged across 2019 to 2023, weather-related crashes ran 744,911 per year with 3,807 fatalities, and crashes involving freezing precipitation specifically accounted for 219,942 of those crashes and 407 of those deaths. FHWA also notes that over 70 percent of the nation's roads are in snowy regions averaging more than 5 inches of snow a year, and nearly 70 percent of the US population lives in them. Here are the seven checks, with the figures behind each one.

1. How much tire pressure do you lose in cold weather?

About 1 PSI for every 10 degree Fahrenheit drop. That figure comes from Case Western Reserve University, where Xiong Yu, chair of civil and environmental engineering, states that a drop of 10 degrees Fahrenheit can lead to a decrease in tire pressure of one pound per square inch. A US Air Force safety notice puts it a little wider, at 1 to 2 pounds per 10 degrees of temperature change.

NHTSA confirms the direction without publishing a number: as the outside temperature drops, so does tire inflation pressure. What NHTSA does give you is the procedure, and the part most people get wrong:

• Fill each tire to the vehicle manufacturer's recommended pressure, which is on the door-frame label or in the owner's manual.

• Do not inflate your tires to the pressure listed on the tire itself. That number is the tire's maximum, not your vehicle's target.

• Check when tires have not been driven on for at least three hours. A warm tire reads high.

• Check at least once a month, including the spare.

There is a fuel cost to ignoring this too. The Department of Energy says under-inflated tires lower gas mileage by about 0.2 percent for every 1 PSI drop in average pressure across all tires.

2. Do you have enough tread for winter?

NHTSA's line is clear: tires are not safe and should be replaced when the tread is worn down to 2/32 of an inch. The penny test is how you check without a gauge. Put a penny in the tread groove with Lincoln's head upside down and facing you. If you can see the top of Lincoln's head, the tire needs replacing.

Here is where I will be straight with you about sourcing. No federal agency recommends more tread for snow, and no federal agency publishes a temperature at which winter tires start outperforming all-seasons. Those numbers come from industry. AAA recommends replacing front winter tires at 4/32 inch and rear tires at 2/32, and suggests switching to winter tires when your local climate consistently drops below 45 degrees F. AAA also notes tires wear unevenly, so check at least three different grooves on each tire.

The one thing NHTSA will say about winter tires: they are more effective than all-season tires in deep snow. Take that as directional, and treat the 45 degree threshold and the 4/32 recommendation as the tire industry's judgment rather than a federal standard.

3. Will your battery start the engine at 10 degrees?

This is the check that prevents the most miserable mornings, and the physics is a pincer. AAA, which is an industry source rather than a government one, reports that a vehicle battery loses 35 percent of its capacity at 32 degrees F, while a cold engine requires up to 50 percent more energy to crank over. Less available power, more power needed, at the same moment.

NHTSA confirms the direction and gives the action: when the temperature drops, so does battery power, so have a mechanic check the battery, charging system and belts before winter.

A note on a number you will see everywhere: the widely repeated claim that a battery loses 60 percent of its power at 0 degrees F does not appear on any AAA, NHTSA or DOE page I could verify. Use the 32 degree figure, which is sourced, and treat the 0 degree claim as folklore.

AAA adds a practical threshold worth keeping: have the battery tested annually once it is three years old, and note that a 30-minute drive helps keep it charged. Short trips in cold weather do not fully recharge a battery, which is how a marginal battery survives all autumn and then dies in January.

4. Is your coolant mixed for the temperatures you actually get?

NHTSA's guidance is to make sure you have enough coolant meeting the manufacturer's specifications, and to check the cooling system for leaks, test the coolant, and drain or replace old coolant as needed.

For the actual numbers you have to go to a manufacturer, which is worth saying out loud. Ford's Motorcraft technical reference gives a 50/50 ethylene glycol mix freeze protection down to minus 34 degrees F and boil protection to 265 degrees F with a sound pressure cap, and warns not to let the concentration fall below 40 percent or exceed 60 percent.

So: 50/50 is the target, and more antifreeze is not better past 60 percent. Test it with a cheap hydrometer rather than guessing. If you topped off with water in August, you have diluted it.

5. What does cold do to your fuel economy or EV range?

More than most people expect, and the Department of Energy's figures are the best sourced numbers in this whole article.

For conventional gasoline vehicles:

• Fuel economy is roughly 15 percent lower at 20 degrees F than at 77 degrees F in city driving.

• It can drop as much as 24 percent on short trips of 3 to 4 miles.

• Expected ranges: 10 to 20 percent loss in city driving, 15 to 33 percent on short trips.

For hybrids, the typical drop is about 30 to 34 percent, reaching 20 to 40 percent in city driving and 25 to 45 percent on short trips.

For electric vehicles, DOE reports fuel economy can drop roughly 39 percent in mixed driving and range can drop by 41 percent at 20 degrees versus 75 degrees. About two thirds of the extra energy goes to heating the cabin. Without using the cabin heater, the figures fall to 8 percent lower economy and about 12 percent lower range. DOE is transparent that those EV estimates come from a 2019 AAA study rather than DOE's own testing, which is worth knowing.

What to do about it, per DOE: precondition the cabin while the vehicle is still plugged in, use seat warmers instead of the cabin heater where you can, minimize idling to warm the car up and instead drive off gently after about 30 seconds, and keep tire pressure correct because it changes with temperature. DOE's blunt framing on warm-up: idling gets 0 miles per gallon.

One habit from the National Weather Service that costs nothing: keep your gas tank near full to avoid ice in the tank and fuel lines.

6. Did you clear the tailpipe?

This is the check that is genuinely about staying alive rather than staying comfortable, and it takes thirty seconds.

CDC's guidance is direct: before you drive after a winter storm, check that your vehicle's tailpipe is clear of snow, because if it is blocked, carbon monoxide can build up quickly inside the vehicle and poison anyone inside. CDC reports more than 400 Americans die each year from unintentional carbon monoxide poisoning not linked to fires, more than 100,000 visit an emergency department, and more than 14,000 are hospitalized.

The related rules from CDC, all of which apply in winter more than any other season:

• Never run your car or truck inside a garage attached to a house, even with the garage door open.

• Always open the door of a detached garage for fresh air when running a vehicle inside.

• If the tailgate is open, open the vents or windows too, because with only the tailgate open, exhaust gets pulled into the vehicle.

• Have a mechanic check your exhaust system every year. A small leak can let carbon monoxide build up inside the car.

CDC lists the symptoms as headache, dizziness, weakness, upset stomach, vomiting, chest pain and confusion, and notes they are often described as flu-like. The reason that matters in a stranded car is that everyone in it feels cold, tired and slightly unwell anyway.

If you do get stuck in snow, NHTSA says to clear any snow from the exhaust pipe and run the car only sporadically, just long enough to stay warm, and not for long periods with the windows up or in an enclosed space. The Wisconsin Department of Health Services puts a number on it: run your heat for 10 minutes every hour, remove snow from around the tailpipe, and crack a window for ventilation. That 10 minute figure is state guidance, not NHTSA's, and NHTSA deliberately says only "sporadically." Either way, the tailpipe gets cleared first.

7. Is the kit in the car, not in the garage?

The National Weather Service publishes the fullest winter vehicle kit list of any federal source, and it is worth copying whole:

• Mobile phone, charger, batteries

• Blankets or sleeping bags

• Flashlight with extra batteries

• First aid kit

• Knife

• High-calorie, non-perishable food

• Spare dry clothing

• A large empty can as an emergency toilet, plus tissues and paper towels

• A small can and waterproof matches, to melt snow for drinking water

• A sack of sand or cat litter for traction

• Shovel, windshield scraper and brush

• Tool kit, tow rope, jumper cables

• Water container

• Candle and matches, for light and in an emergency, lifesaving heat

• Compass and road maps, because, in the NWS's words, you should not depend on mobile devices with limited battery life

NHTSA's shorter list adds one item worth noticing: a first aid kit including a tourniquet, plus personal medicines. If the car does not have one yet, you can assemble it from affordable first aid supplies rather than buying a pre-made kit.

NWS also recommends two habits that cost nothing: fully check and winterize the vehicle before the season begins, and let someone know your timetable plus your primary and alternate routes. Picking those alternate routes is a job of its own, and evacuation route planning technology covers which tools still work when the roads close.

And if you are stranded, NHTSA says stay with the vehicle, avoid overexertion, put bright markers on the antenna or windows, and keep the interior dome light on. One more thing if children ride in this car: the trunk kit needs a few items an adult kit does not, which is what first aid kit essentials for children walks through.

What about washer fluid and wipers?

NHTSA says to make sure the reservoir is full of high-quality winter fluid with de-icer before winter weather hits, and warns that you can go through a lot of washer fluid in a single snowstorm. That is as specific as any authoritative source gets.

I looked for an official freeze point for winter washer fluid and could not find one from any government or standards body. Product labels run roughly from plus 20 degrees F down to minus 35. Buy one rated below the coldest temperature you actually see, and carry a spare jug. Summer fluid freezing in the lines in December is a genuinely dangerous way to lose your windshield.

Frequently asked questions

How much tire pressure do you lose in cold weather?
About 1 PSI for every 10 degree Fahrenheit drop in temperature, according to Case Western Reserve University. NHTSA confirms that tire inflation pressure falls as outside temperature drops, and says to fill each tire to the pressure on the vehicle's door-frame label or owner's manual, not the number molded into the tire sidewall.

What tread depth do you need for winter driving?
NHTSA says tires are not safe and should be replaced when tread is worn to 2/32 of an inch. Use the penny test: place a penny in the tread with Lincoln's head upside down, and if you can see the top of his head, replace the tires. AAA, an industry source, recommends replacing front winter tires at 4/32 inch.

How much battery power do you lose in the cold?
AAA, an industry source rather than a government one, says a vehicle battery loses 35 percent of its capacity at 32 degrees F, and that a cold engine requires up to 50 percent more energy to crank. NHTSA confirms the direction without a figure: when the temperature drops, so does battery power.

How much does cold weather hurt gas mileage?
The Department of Energy says gas mileage is roughly 15 percent lower at 20 degrees F than at 77 degrees F in city driving, and can drop as much as 24 percent on short 3 to 4 mile trips. Electric vehicle range can fall about 41 percent at 20 degrees versus 75 degrees.

Why do you need to clear snow from your tailpipe?
Because a blocked exhaust pushes carbon monoxide into the cabin. CDC says that if the tailpipe is blocked, carbon monoxide can build up quickly inside the vehicle and poison anyone inside. CDC reports more than 400 Americans die each year from unintentional carbon monoxide poisoning not linked to fires.

Should you warm up your car before driving in winter?
Not for long. The Department of Energy recommends minimizing idling to warm the car up and driving off gently after about 30 seconds, noting that idling gets 0 miles per gallon. For an electric vehicle, DOE recommends preheating the cabin while the car is still plugged into the charger, which extends range.

None of this takes a mechanic except the battery test and the exhaust check, and both of those are quick appointments. Do the tires and the tailpipe this weekend. The rest can follow. You never know, but you can always be ready.

Sources: NHTSA, Winter Driving Tips · NHTSA, Tires · US Department of Energy and EPA, Fuel Economy in Cold Weather · US Department of Energy, Keeping Your Vehicle in Shape · CDC, About Carbon Monoxide Poisoning · CDC, Clear Snow from Tailpipes · NOAA National Weather Service, Winter Weather Preparedness · Federal Highway Administration, How Do Weather Events Impact Roads? · Wisconsin Department of Health Services, Winter Weather Safety · Case Western Reserve University, Temperature Drop and Tire Pressure · AAA Northeast, Battery and Winter (industry source) · AAA, When Should You Replace Your Tires for Winter (industry source) · Ford Motorcraft, Ethylene Glycol Coolant Quick Reference (manufacturer source)