Here's Why Your Car Won't Start in Cold Weather

By: Sascha Bos  | 
Wide view of heavy snow covered street with lots of parked, snow-covered cars.
Before you assume that your car's battery is dead, check for these issues that commonly occur when trying to start a car in frigid temperatures. zhengshun tang / Getty Images

The whole "car won't start in the cold" thing can be a big problem for people who live up north, and especially for people who live in really cold places like Alaska, where the temperature drops below freezing. There are a few possible reasons why your car won't start in cold weather.


Condensation in the Fuel System Accumulates

Moisture can build up in your fuel system over time, but you might not notice it until cold weather hits, when water trapped in your fuel lines or fuel pump can freeze. Though, if you're fortunate enough to have a heated garage, you may not encounter this buildup at all.

To prevent frozen water droplets in your fuel lines, use winter fuel and keep your fuel tank as full as possible, so there's less room in the gas tank for condensation to build.


Gasoline Evaporates Less

Gasoline, like any other liquid, evaporates less when it is cold. You have seen this; if you pour water onto a hot sidewalk, it will evaporate a lot faster than it will from a cooler place like a shady sidewalk.

When it gets really cold, gasoline evaporates slowly so it is harder to burn it (the gasoline must be vaporized to burn). Sometimes you will see people spray ether into their engines in cold weather to help them start (ether evaporates better than gasoline in cold weather).


Oil Thickens

Oil gets a lot thicker in cold weather. You probably know that cold pancake syrup or honey from the refrigerator is a lot thicker than warm syrup or honey.

Engine oil does the same thing. So when you try to start a cold engine, the car engine has to push around the cold, gooey oil and that makes it harder for the engine to spin.


In really cold places people must use synthetic motor oils because these oils stay liquid in cold temperatures.

Batteries Struggle

Car batteries have problems in cold weather, too. A battery is essentially a can full of chemicals that produce electrons.

The chemical reactions inside of batteries take place more slowly when the car battery is cold, so the battery produces fewer electrons. The car's starter motor therefore has less energy to work with when it tries to start the engine, and this causes the engine to crank slowly.


All three of these problems ­can trick you into thinking you have a dead battery and make it impossible to start an engine in really cold weather.

To get around this, people either keep their cars in heated garages or use something like a "battery blanket" or "block heater." A block heater is a little electric heater that you plug into the wall to keep the engine warm.