Dear Car Talk:
My mileage drops in the winter. I understand this has something to do with winter, but my question is: What is it about winter that makes mileage drop? — Mary
A bunch of things, Mary. Some mechanical, some behavioral.
When it’s cold out, you may spend more time warming up your car. Even if you don’t sit in the driveway and let it warm up, it takes the engine longer to get to full operating temperature, where it runs most efficiently. Then it cools down more quickly between trips.
In the winter, you may drive places to which you’d ordinarily walk. If you go to a store and need to stop at another store four blocks away, you’d probably enjoy the walk in the summertime. When it’s 25 degrees out, you might drive. And short trips produce poorer mileage.
For every 10 degrees Fahrenheit the temperature drops, your tire pressure drops about 1 PSI. Even if it doesn’t drop enough to turn on the tire pressure warning light, a drop of 2 or 3 PSI will lower your mileage a bit.
When the car is cold, your oil and other engine fluids are harder to move around, which creates more internal engine friction. That also reduces your mileage.
You may be using heated seats, front and rear defrosters, and other accessories that use power. When you use more power, your mileage takes a hit.
Your battery is less efficient in cold weather, forcing the alternator to work harder to keep it charged up.
And finally, in many parts of the U.S., winter blends of gasoline have slightly less energy per gallon than summer blends.
Add it all up, and mileage drops noticeably in cold weather.
What can you do? 1. Overinflate your tires a little bit. If they call for 32 PSI, set them at 35. No harm will be done, and when their pressures drop due to temperature, they’ll be closer to where they should be.
2. Minimize warm up. Unless it’s subfreezing, start the car and go. If it’s 20 F out, let the car warm up for 30 seconds. But skip the unnecessary three-minute warm up, and especially the remote, 20-minute warmup while you wolf down two scrambled eggs and a stack of pancakes.
3. Relocate to Arizona. That’d be my choice.
Got a question about cars? Write to Car Talk write to Ray in care of King Features, 628 Virginia Drive, Orlando, FL 32803, or email by visiting the Car Talk website at www.cartalk.com.
