Car maintenance in winter: what to check before the cold

What does a winter car maintenance checklist include?

A winter car maintenance checklist covers the parts that cold, snow and salt attack: the battery, the tyres, the coolant, the wipers and washer fluid, the oil, the lights, the fuel tank and the underbody. Most of the work is a single visit in October or early November, before overnight temperatures settle at 7°C (45°F). The salt wash and the tank level carry on all winter.

The table below lists each check, when to do it and why it matters in the cold. Every row has its own section further down with the figures and sources behind it, so a reader looking for one item can jump straight to it.

Sources: AAA (battery), AAA (road salt), Consumer Reports, ready.gov, fueleconomy.gov.

Why does a car battery fail in cold weather?

A car battery fails in cold weather because the chemical reaction that produces its current slows down as the temperature drops, while the engine asks for more. The AAA Automotive Research Center reports that a battery loses about 35% of its strength at 0°C (32°F) and about 60% at -18°C (0°F), and that a cold engine can need up to twice the normal current to start.

Cranking power is the current a battery can deliver to turn the starter. Consumer Reports puts it the same way: at about -18°C (0°F) a battery has roughly half the cranking power it has at 27°C (80°F). A battery that started the car without trouble in September can leave it silent on the first frozen morning.

AAA gives average car battery life as three to five years and treats a battery older than three years as a warning sign. Have it load tested before winter, which most parts shops and garages do in a few minutes, and clean any white or green crust off the terminals so the current reaches the starter.

When should you switch to winter tyres?

Switch to winter tyres once night-time and early-morning temperatures are at 7°C (45°F) or below most days. American Tire Distributors calls this the 45-degree switch: a winter tyre's rubber compound stays flexible in freezing temperatures and grips better than all-season rubber below 7°C (45°F). A winter compound is the soft rubber blend used in winter tread.

The 7-7 rule says the same thing in Celsius. CAA North & East Ontario advises fitting winter tyres once the temperature has stayed at or below 7°C (45°F) for seven days in a row, and taking them off when it stays at or above 7°C for seven days. Above that point a soft winter tread wears quickly on warm, dry roads.

Consumer Reports recommends dedicated winter tyres on steel wheels where snow and ice are constant, and says it is safest to replace all four tyres at once. Cold also lowers the pressure in every tyre, so check it after each cold snap; the details are in how much tyre pressure drops in cold weather.

Is your antifreeze ready for winter?

Antifreeze is ready for winter when the coolant is the type your manual specifies and mixed at the right ratio. Consumer Reports recommends a 50/50 mix of antifreeze and water; very cold climates can call for 60% antifreeze and 40% water, or 70% and 30%, and never a richer mix than that.

Freeze protection printed on a bottle assumes the mix is exactly right, so test the coolant in the reservoir with an inexpensive hydrometer or test strips rather than trusting the label. Check the level with the engine cold, and look at the hoses for cracks or soft spots. How often the coolant itself needs replacing depends on its type: see how often to change coolant.

Wipers, washer fluid and lights: what to replace before winter?

Replace wiper blades that streak or chatter before the first snow. Consumer Reports found that blades can lose effectiveness in as little as six months and suggests replacing them as often as twice a year. A blade that has spent a summer in the sun is usually the one that smears salt across the glass in December.

Fill the washer reservoir with a winter-blend fluid that contains an antifreeze agent, as Consumer Reports advises. Summer fluid can freeze in the reservoir or on the windscreen, and road salt means the washers run far more often in winter than in any other season.

Check every bulb, headlights, brake lights, indicators and fog lights, and clean the lenses. Ready.gov lists the wiper equipment and the washer fluid level among the checks to have done before an emergency, alongside the antifreeze, the battery and the ignition system.

What oil should you use in winter?

Use the oil grade your owner's manual lists for cold weather, which for most modern engines is a multi-viscosity oil. A multi-viscosity oil is rated for two temperatures, and the number before the W is its winter rating: the lower it is, the more easily the oil flows at a cold start. Consumer Reports recommends a W-rated oil and checking the manual first.

Fueleconomy.gov gives the reason it matters beyond starting: cold engine oil and cold drive-line fluids raise friction, and the engine takes longer to reach its efficient temperature. If the oil change interval runs out within a few hundred miles of winter, doing it in autumn puts fresh oil of the right grade in the engine for the coldest months.

Should you keep your fuel tank full in winter?

Keep the fuel tank full or close to it through the winter. Ready.gov advises a full tank in case of evacuation or a power outage, and notes that a full tank also keeps the fuel line from freezing. This works because less empty space in the tank leaves less room for moist air to condense into water.

A full tank also matters if the car is stuck in snow or a long closure, because the engine may be the only source of heat. Run it only in short spells and keep the exhaust pipe clear of snow, so exhaust gas does not collect inside the cabin.

How does road salt damage a car, and how do you prevent it?

Road salt and liquid de-icers speed up rust on the underbody, the brake lines, the fuel tank, the exhaust, electrical connections and any chip in the paint. A 2017 AAA survey estimated that US drivers paid $15.4 billion in rust repairs over five years, about $3 billion a year, averaging almost $500 per repair, and that 22 million drivers had rust damage in that period. These are US figures, not UK ones.

AAA's prevention advice is practical. Wash and wax the car before winter, touch up chips and scratches that expose bare metal, wash it often during the salt season with special attention to the undercarriage, use a car wash soap rather than washing-up liquid, and avoid driving right before, during and after storms, when the chemicals on the road are most concentrated. In spring, clean the underbody thoroughly once more.

Are cars less efficient in winter?

Cars are less efficient in winter, and short trips suffer most. Fueleconomy.gov reports that a petrol car's city fuel economy is roughly 15% lower at -7°C (20°F) than at 25°C (77°F) and can drop as much as 24% on trips of 3 to 4 miles. The causes are thicker cold oil, a longer warm-up, lower tyre pressure, denser air, winter petrol blends with slightly less energy, and the heater and defrosters.

As an example calculation, a car rated at 30 MPG (imperial) in city driving would return about 25.5 MPG at -7°C (20°F) (30 × 0.85) and about 22.8 MPG on 3 to 4 mile trips (30 × 0.76). Idling to warm up makes it worse, since idling gets 0 MPG: fueleconomy.gov says most manufacturers recommend driving off gently after about 30 seconds. To see the winter dip in your own numbers, read tank-to-tank fuel economy across the seasons.

Source: fueleconomy.gov, Fuel Economy in Cold Weather.

How do you prepare an electric car or hybrid for winter?

Prepare an electric car for winter by heating it while it is still plugged in. Fueleconomy.gov reports that at -7°C (20°F) an EV's range can drop by 41% with the cabin heater on, that about two thirds of the extra energy goes into heating the cabin, and that without the heater the range loss is about 12%. Preheating on the charger takes that heat from the grid instead of the battery. How much range EVs lose at each temperature, in lab tests and in real driving, is compared in electric cars in cold weather.

Seat heaters warm the driver for less energy than heating the whole cabin, which fueleconomy.gov also recommends. A hybrid loses about 30% to 34% of its fuel economy in the cold, so the same habits help it: combine short trips and park in a garage when you can. Cold-weather range loss is temporary and different from long-term wear, covered in how long EV batteries last.

An electric car still has a 12-volt battery that powers its computers and locks, and it can fail in the cold like any other car battery. Test it at the same visit as the tyres and wipers.

What should be in a winter car emergency kit?

A winter car emergency kit should let you clear the car, get traction and stay warm while you wait. Ready.gov lists an ice scraper and cat litter or sand for traction, and a fuller winter kit includes a snow brush, a small shovel, warm blankets, gloves, a torch, jump leads, water, snacks and a phone charger.

Keep the kit in the car from the first snow until spring rather than packing it before a trip. For a longer drive in winter, the road trip car checklist covers the full kit and the checks to make before leaving.

What does a sample winter maintenance plan look like?

This sample plan is for a petrol car in a region with regular snow, driven daily and parked outside. Shift the dates to your own climate: the trigger is the temperature, not the calendar. WrenchTime, a car and motorcycle maintenance app for iPhone, has a Winter Prep kit that logs the tyre change, tyre pressure check, battery check, coolant flush and wiper blades as one entry, and it can repeat every year with a reminder before the date.

• Early October Book the winter tyre fitting before the garages fill up, and do the autumn oil change if one is due.
• Before the first freeze Have the battery load tested, test the antifreeze mix, replace streaking wipers, fill the washer with winter fluid and check every bulb.
• When nights stay at 7°C (45°F) Fit the winter tyres, set the pressure cold to the door placard and put the emergency kit in the boot.
• Every week or two of salt Wash the car and the underbody, and keep the tank close to full.
• After each cold snap Check the tyre pressure again, since every drop in temperature takes a little more.
• Spring, when days stay above 7°C (45°F) Swap back to all-season tyres, wash the underbody thoroughly and refill the washer.

Put winter prep on a yearly reminder

Set Winter Prep, or a Seasonal Tyre Change, as a yearly recurring job in WrenchTime and the reminder arrives before the cold does; the completed entry keeps the date, the odometer, the cost and the invoice, and the next one is already scheduled. It is one of 12 maintenance kits, and the steps are in how to schedule maintenance and reminders. The free version covers 1 vehicle with 2 maintenance entries per month, and WrenchTime Pro removes the limits.