Car won't start in cold weather

Symptoms

• Slow, labored cranking in cold weather
• Starts fine once temperatures warm up
• Battery seems fine in warm weather
• May crank longer before catching

Likely causes

• CommonBattery capacity reduced by coldCold cuts a battery's effective cranking power significantly, exposing a marginal battery.
• CommonThickened engine oil increasing cranking resistanceThicker cold oil makes the engine harder to turn over, especially with old or wrong-weight oil.
• CommonWeak battery that was already near end of lifeCold often reveals a battery that was borderline all along.
• PossibleFuel system icing or condensation (older/diesel vehicles)Water in fuel or a diesel that hasn't been winterized can struggle in extreme cold.
• PossibleGlow plug issue on diesel enginesDiesels rely on glow plugs to warm cylinders before cold starts.

What to do

1. Turn off accessories like heated seats, headlights, and the radio before trying to start, to save battery power for cranking.
2. Try starting the car; if it cranks slowly but eventually catches, the battery is marginal and worth testing soon.
3. If it won't catch at all, try a jump-start from another vehicle or a jump pack rated for cold weather.
4. Check that you're using the correct oil viscosity for cold weather as listed in the owner's manual.
5. Have the battery load-tested; batteries typically weaken with age and cold exposes that weakness first.
6. For diesel engines, make sure winter-blend fuel was used and check that the glow plug light cycles normally before starting.
7. Consider a battery blanket, garage parking, or a trickle charger/battery tender for repeated cold-start trouble.
8. Replace a battery more than 3–5 years old before winter rather than waiting for it to fail.

Tools and parts

• Jumper cables or jump box
• Multimeter (optional)

When to call a pro

If a healthy, tested battery still won't crank the engine in the cold, have a shop check the starter and, on diesels, the glow plug system.

Safety