How's Your Gas Mileage This Winter?

About a month ago, I noticed something terrible. As gas prices were going up, my mileage was plummeting.

It dropped from 25 miles a gallon to 17 (no hybrid here), enough to make me consider joining the modern age and getting rid of my 20-year-old car.

First, however, I tried everything I could to up the efficiency. I replaced the tires and spark plugs. I got it tuned up. But, no luck. The needle in the gas tank was dropping like the altimeter on a falling plane. 

So, I hit up my mechanic buddy, George Loughran, who had the answer right away.

“Five miles a gallon? That's the winter blend.”

Oh yeah, the gas we Californians put in our cars from November through March is dirtier and contains additives such as butane, which burn at a higher vapor pressure. They make the gas cheaper, but far less efficient than the summer gas, which burns at a much lower pressure and is more pure.

Butane, for example, would boil off as a gas in summer, but can help fill a tank in the winter.

The summer and winter switch isn't much thought about, but became an issue in October when Gov. Jerry Brown asked the Air Resources Board to allow the winter gas to be sold before Oct. 31, because gas prices were reaching record highs.

So, we get cheaper gas, but have to use more of it? I'm not sure how the math works here.

How is it working in your tank? Are you Prius and Volt owners feeling smug in the smog?

Should I take the plunge and get something more fuel efficient, as opposed to a car with no payments?

P.S.: California gas prices averaged just over $4 a gallon in 2012, a record, beating last year's high of $3.50 a gallon. Nationwide prices averaged $3.60 a gallon, according to this story in the Los Angeles Times.