Why Won’t My Car Start in the Cold?

Cold weather is one of the most difficult things any car will have to deal with. Fluids get thicker, tolerances get tighter, friction increases, and certain parts don't handle the cold as well as others. It all makes for a major question mark whenever you hop in the driver's seat and turn the key.

Sometimes, your car just won't go, leaving you wondering what's gone wrong this time. It could be one of many reasons, and it's not always easy to figure out what the cause is. It might not cost a thing to fix, and other times it could be hundreds or even thousands to repair. 

Here are some of the reasons your car won't start in the cold, and what you can do about it.

Dead battery

One of the most common reasons a car won’t start in the cold is because the battery is dead. A car’s battery provides the electrical current needed to start the engine, and if it’s too weak, the engine won’t turn over. This is especially common in older cars with weaker batteries. If your car is having trouble starting in the cold, it’s a good idea to get your battery tested to see if it needs to be replaced. 

A good battery will have cranking health, or cold cranking amps, that meet or exceed the battery’s rating. The reserve capacity should also be at least what the battery is rated for or your engine might not start if you need to crank it over several times to fire up. And if your battery fails a test or the decision shows it’s weak, don’t delay. For $100 to $230, it’s not worth getting stuck out in the cold.

Fuel restriction

Another reason your car might not be starting is that the fuel isn’t reaching the engine. In very cold weather, fuel can actually freeze in the lines leading from the tank to the engine. This prevents it from getting where it needs to go and results in a no-start situation. The fix for this is usually pretty simple –just let your car thaw out for a bit and try starting it again. 

However, a restriction in the fuel can be caused by exacerbated by a dirty fuel filter or dirty fuel injectors. Thickened fuel or ice particles can get jammed up, preventing fuel flow. Fuel system cleaner is a great product to use in the fall to clean injectors, and a replaceable fuel filter should be changed annually.

Frozen starter

Another possibility is that the starter itself is frozen. The starter is responsible for getting the engine going by receiving a major electrical current from the battery, and if it’s frozen, it can’t do its job. This is usually caused by moisture getting into the starter. 

Sometimes, warming your car is all it takes to get it going again. Other times, the water droplets can freeze, expand, and cause permanent issues – even corrosion. Or, the solenoid can burn out on the starter. If heat doesn’t do the trick, your vehicle might need a starter replacement. 

Oil is too thick

Another starting issue has to do with oil. In sub-zero temperatures, engine oil can get so thick that it won’t flow through the engine properly. That can cause all sorts of problems, from decreased fuel efficiency to complete engine failure. 

The solution here is also relatively easy – just make sure you’re using the right type of oil for your car and the conditions you drive in. Some vehicles recommend a thinner oil viscosity for winter conditions, which helps prevent excessive resistance to cranking. It’s particularly important for turbocharged engines since oil starvation can quickly cause them to overheat – an ironic problem in the cold.

Coolant frozen in engine

Thickened oil isn’t the only fluid-related starting issue, either. Cold weather can also cause your coolant to freeze, which will prevent it from circulating through your engine and keeping it at the proper temperature. This can lead to all sorts of problems, so it’s important to keep an eye on your coolant levels and condition and make sure they’re correct before winter hits.

Normally, coolant should be a 50/50 mix with distilled water. If the coolant mixture is more water than coolant, then the protection against freeze-up is compromised. For instance, if your coolant is only good to 0F but it drops to -20 or -30F, it can freeze and crack the radiator, the water pump, the thermostat housing, or even the engine block itself as the water expands. It can range from minimal damage to catastrophic.

Other issues

Of course, there are other potential reasons why your car might not be starting in the cold weather, and it might not be related to the temperature at all. It could be something as simple as a loose wire or a bad connection somewhere in the electrical system. Or, it could be a more serious problem like a blown head gasket or a seized engine. The same issues that prevent your engine from starting in the hot weather can occur in the cold.

Don’t let the cold weather keep you from getting where you need to go. With a little bit of knowledge and preparation, you can make sure your car is ready to face the elements. And if worst comes to worst, you know where to turn for help.

AutoZone has everything you need for your car to dominate the cold weather. Find your winter fluids, parts, and accessories in stock in-store or online. 

Helpful Winter Resources

FAQ/People Also Ask

How do I fix my car if it won’t start in the cold?

The repair depends on why your car won’t start. In some cases, you’ll need a new part installed like the battery, while other times it’s simply a matter of warming the car. 

Why won’t my car start in the winter?

Cold weather can wreak havoc on cars. Common starting issues range from a dead battery or frozen starter to the wrong engine oil or coolant strength, and a mechanic may need to diagnose the issue.

How do you warm up a car that won’t start?

You may be able to shroud your car with a tarp and put a heater underneath to warm it, or installing a magnetic oil pan heater can help.  Sometimes, it needs to be towed to a warm garage to thaw out.

How do you unfreeze a car engine?

If the engine oil is too cold, a block heater can unfreeze it. If it’s the engine coolant that has frozen, the car usually needs to be brought to a warm garage to get it going again.

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