Why does my car's fuel efficiency change so much between summer and winter?

Dear Car Talk

Dear Car Talk | Jan 01, 2000

Dear Tom and Ray:

I have a 1988 Chevy Nova with 115,000 miles on it. It is well-maintained. During
the summer, it gets a decent 34 miles per gallon, but in the winter, it gets only
about 29 mpg on the same highway with the same driver. Why? -- Brian

TOM: 'Cause it's cold out, Brian baby! Look at my brother. He eats 11 pink-
frosted doughnuts on the average winter morning instead of his usual eight during
July and August.

RAY: The reason cars run less efficiently in cold weather is because gasoline
doesn't vaporize as well. The carburetor sends vaporized fuel into the cylinders,
and in cold weather, some of it condenses and turns back into liquid gasoline.
That portion doesn't burn and is essentially wasted. And that accounts for most
of your 15 percent reduction in mileage.

TOM: Most cars spend more time warming up and idling in the winter, and in some
areas, there's more wind resistance as well. But the loss of efficiency in
gasoline combustion due to cold weather accounts for the vast majority of the
lost mileage.

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