Most winter car advice is a list of things to buy. This is the version we would give a customer standing at the counter in November, in the order the Michigan winter actually breaks things, and with the parts you can check yourself separated from the parts you cannot.
Start with the battery, because cold is what exposes it
Cold does two things to a battery at once. It thickens the oil, so the starter has to work harder, and it slows the chemical reaction inside the battery, so there is less available current to do it with. A battery that has been quietly failing since August will start the car every day right up until the first morning below twenty degrees, and then it will not.
The tell is not a warning light. It is the sound: a starter that turns over a half-beat slower than it did last week, or headlights that dim noticeably while the engine cranks. If you have either, have the battery tested before the cold snap rather than after it. A load test takes a couple of minutes and gives you a number rather than an opinion.
Two other things worth knowing. Battery terminals corrode faster in winter because of the temperature cycling and the salt-laden air, and a furred terminal can look like a dead battery. And on most modern cars, a replacement battery has to be registered to the vehicle so the charging system runs the right profile for a new one rather than the profile it learned for the old one.
Tires: pressure first, tread second, age third
Tire pressure drops roughly one PSI for every ten degrees the temperature falls. A car set correctly at seventy-five degrees in September is meaningfully soft by the first hard freeze, and the tire pressure light usually comes on somewhere around twenty-five percent low, which is well past the point where handling and wear have already been affected.
Check the pressures cold, before the car has been driven, against the number on the sticker in the driver's door jamb and not the number on the tire sidewall. The sidewall figure is the tire's maximum, not the vehicle's specification.
On tread, the legal minimum is 2/32 of an inch, but wet and slush stopping distance falls off a cliff well before that. In a Michigan winter, 4/32 is the honest point to start planning replacement rather than the point at which you have to. And a tire has a date code on the sidewall, four digits giving the week and the year it was made. Rubber hardens with age whether the car is driven or parked, so a tire with deep tread and a code six or seven years old is still a tire to think about before winter, not after it.
Winter tires, honestly
Winter tires are a real upgrade and they are not necessary for everybody. The rubber compound stays pliable below about forty-five degrees where an all-season hardens, which is where most of the grip difference comes from rather than the tread pattern. If your commute includes hills, or you are out early before the plows, they earn their money. If you drive mostly cleared main roads in daylight, a good all-season with real tread depth is a defensible choice. What is not defensible is two winter tires on the front and two all-seasons on the back.
The fluids that actually matter in the cold
- Coolant. The concern is not the level, it is the mix. Coolant tested with a refractometer tells you the freeze point, and a system that has been topped up with water over the years can be a lot closer to freezing than anyone expects. A frozen block is not a repair, it is an engine.
- Washer fluid. Summer fluid freezes in the lines and in the reservoir, and it tends to do it on the first morning you need it behind a salt truck. Winter-rated fluid is a few dollars and the difference between seeing and not seeing.
- Oil. The viscosity your engine asks for already accounts for cold starting, which is what the W in 5W-30 means. What matters more is that the oil is not overdue, because oil that has sheared down takes longer to reach the top of the engine on a cold morning, and that is exactly when it is most needed.
Wipers and the things you only notice in weather
Wiper rubber hardens and takes a set over a summer of heat, and a blade that smeared a little in October will chatter and skip in freezing rain. Replace them before the season rather than during it. While you are there, lift each blade off the glass and look at the rubber edge: a blade that is torn or has a wavy edge is finished regardless of how old it is.
Two habits that cost nothing. Do not use the wipers to break ice off the windshield, because that is how the linkage strips and the motor burns out. And lift the blades off the glass overnight when freezing rain is forecast, so they are not frozen down in the morning.
Salt is the part that decides how long the car lasts
Everything above is about getting through a season. This is the one that decides whether the car is worth keeping in five years. Michigan road salt attacks the underside, and the parts that matter are structural rather than cosmetic: the subframe, the rocker panels, the brake lines and the fuel lines. Surface rust on a body panel is an appearance problem. A pitted brake line is a failure waiting for the first hard stop.
The single most useful habit is washing the underside, not just the paint. Any car wash with an undercarriage spray is doing more for the car's life than any wax. Do it after a thaw rather than during a freeze, so the water drains rather than sitting.
What is worth having somebody look at
You can check pressures, tread, wipers and washer fluid in your own driveway in ten minutes. What is worth a lift is the part you cannot see: the condition of the brake and fuel lines, whether the exhaust has started rotting at the low points where winter condensate pools, whether the coolant will actually take the temperatures forecast, and whether the battery has the capacity the label claims.
That is a multi-point inspection, and at First Call it is free with any visit. Come in for the oil change you are due anyway in October or November and you get the winter check as part of it, with a written green, amber and red report rather than a verbal list. Knowing in November what needs doing in January is the whole point.