Why Won’t My Car Start in the Cold?

Discovering your car won’t start on a freezing morning can quickly ruin your day. Of course, a dead battery is the most likely culprit when an engine can’t turn over, but there are other reasons why your car won’t start in the cold.

Here are the most common reasons, what to do if it happens and how to prevent cold-weather starting problems.

Dead Battery

Even a battery in good condition loses half its potential power at 0 F. At the same time, motor oil and other fluids thicken, requiring more battery power to start your vehicle than on a warm day. That’s why a dead battery is one of the most common reasons a car won’t start in the cold.

Safety first! Never attempt to jump start a frozen battery — it can explode. Car batteries contain sulfuric acid that can cause serious burns. Always wear gloves and eye protection when working around a battery or jump starting a car. If you come into contact with battery acid, flush with water and get medical attention immediately.

What to do:

• Jump the battery. Use a helper car with jumper cables or a portable jump starter to give the battery a boost.
• Service the battery terminals. Remove the terminals and clean corrosion from the posts and terminals with a wire brush. Clean, tight battery terminals provide solid electrical connections for maximum current flow.
• Clean the battery. Use a plastic brush and weak solution of one-quarter cup baking soda and one-quart clean warm water to scrub the top of the battery. Dry, then check and top off the battery fluid with distilled water if needed.
• Turn off unnecessary electrical devices to help the battery send all its starting power to the engine.

How to prevent:

• Install a battery blanket. A heated blanket keeps the battery from losing voltage and power in cold weather.
• Replace the battery. If your battery is more than three years old, replace it with the highest cold cranking amps (CCA) rating that will physically fit into your vehicle.

Thick Motor Oil

As temperatures drop, motor oil becomes thicker and harder to push through the engine. Contaminants and sludge buildup also thicken oil. Consider switching to full synthetic motor oil that has better cold-weather properties.

Always choose an oil with the vehicle manufacturer’s recommended viscosity rating. The two most common viscosities are SAE 5W-30 and SAE 10W-30. The lower the number, the thinner the oil, so it flows better at low temperatures. The “W” means the oil is suitable for winter driving.

What to do:

• Warm the engine. Install a self-stick warmer onto the oil pan. In extreme climates, have your repair shop install an in-the-block heater.

How to prevent:

Frozen Fuel System

Lower temperatures make it harder for gasoline to vaporize. And as temperatures fluctuate, condensation (water) can build up in the gas tank. Because water is heavier than gasoline, it collects on the bottom of the tank and eventually makes its way into the fuel lines. When temperatures drop below 32 F, the water can freeze, blocking the fuel lines or jamming the fuel pump.

Older carbureted vehicles face two problems. One is carburetor icing due to water vapor freezing onto the throttle valve, which hinders gasoline from vaporizing. The other is a frozen shut butterfly valve, preventing air from entering the combustion chamber.

What to do:

• Warm the fuel lines. Wrap warm towels around them and place a shallow bucket with hot water under the fuel tank.
• For carbureted engines only, use a spray carburetor cleaner or starter fluid to dissolve frost buildup in and on the carburetor. Always reinstall the air cleaner and let the spray dry before starting the engine.

How to prevent:

Defective Engine Sensors

Cold temperatures call for richer fuel mixture when starting your engine. A defective coolant temperature or malfunctioning air intake temperature sensor can cause a lean air/fuel mixture, making the engine difficult to start in cold weather.

What to do:

How to prevent:

Problem Alternator or Starter Motor

A weak or worn alternator or a slipping drive belt will drain the battery, especially if you’re using your headlights or other high-current-draw accessories. On a freezing day, worn starter motor brushes cannot conduct sufficient power from an already weakened battery to spin the engine, so the car won’t start.

What to do:

How to prevent:

• Check the alternator drive belt. The belt should not deflect more than a one-half inch when pressed with your thumb along its longest run between pulleys. Replace if there are any signs of wear.
• Check the charging/starting systems. Have your repair shop perform an alternator voltage output test and starter motor draw diagnostic test. Or invest in an inexpensive multimeter and DIY.
• Reduce stress on the charging system. When possible, turn off unnecessary electrical accessories and devices until the engine reaches operating temperature.

The Final Word

If you have access to a heated garage, use it. Consider a garage heater to take the chill. Winterizing your car is the best protection against being stranded.

Whether you DIY or have the pros service your car, change or flush your vehicles fluids, check all filters and make sure the heater and defrosters are working properly. Replace wiper squeegees and check that the battery, ignition, charging and starting systems are all in good shape before bitter cold weather sets in.