Why Won't My Car Start When It Is Cold?

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On cold mornings, if a car does not start, the two most likely culprits are the battery and the choke on the carburetor. If the car has a fuel injection system, it is necessary to take the car to a professional for diagnosis.

According to Bill Hodges, a technician with AAA, many people go without having their batteries checked as long as their cars continue to start; however, extremely cold temperatures cause car batteries to age much more quickly. Batteries operate with a chemical reaction, and cold temperatures make that reaction slow down, hampering its ability to function correctly. Regularly checking battery terminal ends for corrosion helps keep a battery working longer.

If the problem lies within the carburetor, the choke must be able to close and open freely. By "choking" off the air supply to the carburetor, this piece makes the fuel/air mixture richer. This also builds low pressure within the throat of the carburetor, pulling more fuel through the central circuit. In extremely cold temperatures, it is sometimes necessary to change the temperatures at which the choke opens and closes, altering the richness of the fuel mixture. Turning the housing to build tension on the choke causes the housing to close at a higher temperature. Lessening the tension on the housing forces it to close at a lower temperature, leading to a leaner mixture. To find the right setting for a particular car requires experimentation to find the right setting.