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Why your car won’t start when it’s cold—and how to fix it

car breakdown on the road

Stranded in the cold because your car won’t start? Cold weather can be especially hard on parts of a vehicle like the battery, alternator, fuel system, and engine oil.

This guide covers the four most common reasons a car won’t start in cold weather, how you can fix it, and ways to prevent it so you can stay on the road with your heat on full blast.

1. A weak or dead battery can keep your car from starting in the cold

A weak or dead battery is one of the most common reasons a car won’t start during the colder months. If your car’s battery is weak, the engine will turn over slowly when you try to start it. If it doesn’t start right away, it’ll eventually stop turning over altogether as the last of the energy is drained from the battery.

If the battery is completely dead, you might hear a clicking sound when you try to start it, but the engine won’t turn over.

Cold temperatures reduce a battery’s output by slowing down the chemical reaction taking place inside it, so less power is available to start the engine. Plus, engine oil gets thicker when it’s cold, making the engine harder to turn over, requiring more power from the battery.

The combination of these factors can cause a battery that was weak but still working fine in warmer weather to suddenly fail, leaving you stranded with a car that doesn’t start.

How do I fix a dead car battery in the cold?

To get your car running again—at least temporarily—you’ll likely just need a jump start. For that, you’ll either need a battery booster pack, or a set of jumper cables and a friend with a running car.

Check your owner’s manual for jump starting instructions. Following the proper procedure will help keep you safe and ensure you don’t damage your vehicle or anyone else’s in the process.

Once your car is started, keep it running for a bit so the alternator can recharge the battery. If your battery continues to die, it may need to be replaced.

How do I keep my car battery from dying in cold weather?

Since cold weather weakens car batteries, it’s a good idea to have yours tested before the weather drops below freezing. Take your car to an auto parts store or a mechanic—many places will test the battery for free. If the test shows your battery is on its last legs, you’ll want to replace it before cold weather arrives.

Keep in mind, car batteries typically only last three or four years. If yours is getting to that age (you can tell by looking at the date stamped on the top), you’ll want to have it tested more frequently to avoid being stranded, or simply replace it before the next cold season.

If testing shows that your car’s battery is fine but it continues to die, it may not be getting enough of a charge from the alternator. In that case, you’ll want to check the alternator next.

2. Can cold weather affect the alternator?

Yes. The alternator charges the battery anytime the engine is running. In cold weather, the alternator must work harder to keep the battery charged since the battery is weaker when it’s cold.

It may be time to have your alternator checked if:

  • Your battery is weak or dies again and again but tests show that it’s okay
  • You jump start your car but it immediately dies after the jumper cables are disconnected
  • The battery warning light on your dash comes on when the car is running

The same places that test your battery—mechanics and auto parts stores—should be able to test your alternator as well. If the test shows that it’s bad, you’ll need to have it replaced.

How to fix alternator problems in the cold

If you have your alternator tested and the results show that it’s bad, you’ll need to get a new one. Alternators are relatively easy to replace, but they’re connected to the car’s electrical system and are typically run by an engine belt, so it’s a good idea to have the job done by a professional mechanic.

Make sure your car’s alternator can handle the cold

Before the weather turns cold for the season, it’s a good idea to get your alternator tested. You can have this done at the same time you have your battery tested at a mechanic or auto parts store. If testing shows that your alternator needs to be replaced, you can have it done ahead of time to avoid being stranded in the cold.

3. There’s a problem with the fuel system

If the battery is good and the engine turns over but your car still won’t start, the fuel system may be to blame. Over time, water can build up in the fuel tank due to condensation. If this happens, the water can get into the fuel line and freeze, blocking fuel from getting to the engine.

How to fix a cold weather fuel system problem

The most surefire way to get your engine running again if the fuel line is frozen is to move the car inside to a heated space and let it warm up. This may be difficult if your car won’t start, though, so there are other options you can try first.

Buy a bottle of gas line antifreeze or fuel system conditioner—found at most auto parts stores, hardware stores, and gas stations for a few dollars per bottle—and add it to your gas tank. Fill the tank the rest of the way with high quality gasoline from a reputable gas station and try to start the car again.

You can also try heating your car from outside by placing a bucket or pan of hot water under the fuel line to try to thaw it out enough to get your car running.

If these methods don’t work, it’s time to call a tow truck and have your car moved into a heated garage.

Maintain your car’s fuel system in the cold

The easiest way to keep your car’s fuel system functioning properly in cold weather is to keep your gas tank full as much as you can. The more gas that’s in the tank, the less space there is for condensation to build up when temperatures fluctuate, keeping water content to a minimum.

If you drive a flex fuel vehicle that can run on E85 (85 percent ethanol, 15 percent gasoline), it’s a good idea to use regular gas when it’s cold out. While E85 is resistant to freezing, it’s harder to ignite in cold weather, so your engine may not start as easily when using it.

4. Cold engine oil can make it harder to start your car

When you try to start your car, the engine may turn over slowly and then stop. This could be because the battery is weak, but part of the problem might also be that the engine oil is too thick. If you have your battery and alternator tested and both are fine, engine oil could be the culprit.

Cold weather causes oil to thicken, making it harder to pump and causing additional strain on the starter and battery when trying to start the engine. This problem could be exacerbated if you use the wrong type of oil in your engine.

How to fix engine oil problems

If you suspect thickened engine oil is to blame for your car not starting in cold weather, the first thing you should do is check your oil and top it off if it’s low. While you’re checking it, see if it seems to be a normal consistency, or if it seems thick or sludgy.

If it seems too thick, or if you’re not sure if it’s right, take your car in for an oil change. If you’re the do-it-yourself type and want to save some money, you can get started performing maintenance at home.

What type of oil should I use in winter?

Whether you take it to a mechanic or change the oil yourself, make sure the right type of oil is used in your car’s engine. Engine oils vary by viscosity, or resistance to flow. The higher the viscosity, the harder it will be for your engine to pump the oil. Each engine is designed to run on certain oil viscosities, so check your owner’s manual to ensure you’re using the right one.

To keep yourself safe on the road during cold weather, try to prevent these issues before they arise so you won’t be stranded. There are steps you can take in the fall to make sure your vehicle is ready when cold weather hits.

Related links:

If your car leaves you stranded, you might not be close to home. Be prepared for anything by checking out the essential things to keep in your car at all times.

As the calendar flips from one year to another, it’s a good reminder to do a little car maintenance. Check out this new year checklist for your vehicle.

Now that you know how to make sure your car starts in the cold, make sure you have the right car insurance coverage, too.

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