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Click & Clack the Tappit Brothers (MIT Alumni Tom and Ray Magliozzi) of the fabulous NPR Radio program "Car Talk" say it is normal to lose about 10% of your gas mileage in cold weather.

Car engines are like Human engines. It takes more fuel to warm you up to operating temperature and keep you there in the cold than in the heat.

The human body has a temperature management system located in the center of the hypothalamus that acts as a thermostat. Blood flowing through the gland is measured for heat and the gland detects changes in body temperature and sends signals to the rest of the body to keep it in this narrow range of optimum performance. Your car has an engine-management system that performs the same function for your fuel injectors to reach the optimum air to fuel ratio for any given demand.

The system does not even try to determine the most efficient fuel to air ratio until the engine is up to full temperature. In cold weather the computer relies on a program that measures coolant temperature, engine rpm, throttle position and airflow sensor volume and temperature readings.

At this point the system is not working off information coming from the oxygen sensor which is referred to as the "open loop" operation which is a richer air to fuel ratio than when the engine is fully warmed up and the engine management system takes over, making several adjustments a second for each injector.

Another factor is the density of winter air being greater than of the spring and summer months causing more air to be available in the same cubic space so the system adjusts by adding more fuel to the mixture.

For some of the most informative fun you can imagine with automobile issues I recommend that you go to CarTalk.Com and peruse the site and follow that up by listening to a one hour broadcast of Car Talk. My bet is that you will be hooked!

Learn more about this author, Derek R. Snow.
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