How much is good gas mileage worth? Consider that Ford Motor Co. sent my family $1,025 over the past year because our car doesn't get the fuel efficiency Ford had claimed.

Usually, the cost of gasoline pokes holes in your wallet one fill-up at a time, but seeing the dollar difference better efficiency would make all at once was an eye-opener.

Considering that gas prices are hovering close to $3.50 a gallon, even a small difference in efficiency can add up to real money, and cars last a long time. The average car on U.S. roads is more than 11 years old.

It's good to remember that simple things like low tire pressure, aggressive driving habits and keeping a roof rack on your vehicle can result in lower gas mileage and cost you money.

So, why did Ford send me $1,025?

The company is in the process of mailing checks to people who bought or leased a 2013 or 2014 hybrid or plug-in Fusion, C-Max, or Lincoln MKZ, or a 2014 Fiesta. Ford said it found "an error with fuel economy ratings for certain vehicles" and decided to send customers payments to make up for the difference.

Payments range from $125 to $1,050. If you own one of those models, no action is needed to get a check.

My family, which bought a 2013 C-Max hybrid, received a check for $475, but Ford also sent a check for $550 last year when the company first downgraded the car's mileage claim.

So, the combined city/highway gas mileage rating for our C-Max went from the advertised 47 mpg, down to 43 mpg last fall, and now to 40 mpg.

Let's do the math.

Most people drive about 12,000 miles per year, and we expect to own our car for at least 10 years. At 47 mpg, that works out to 2,553 gallons of gas over a decade, which at $3.50 per gallon would cost $8,936.

At 40 mpg, we would need another 447 gallons, and pay an additional $1,564 over 10 years (if the price of gas remained constant).

Buy a car that gets 20 mpg instead of 40, and you can add a whopping $10,500 in fuel expense - more than $1,000 a year - to the ownership cost over a decade.

Every mile-per-gallon is worth something, but the value increases with less-efficient cars. The difference between 24 and 26 mpg, for example, saves more gas and money than the difference between 38 and 40 mpg, because at lower efficiency the incremental gains are larger.

The average fuel efficiency for new cars and trucks in the U.S. is just under 24 mpg. Someone who gets 26 mpg instead would save $135 yearly.

That's a good incentive to keep tires properly inflated and go light on the pedal. It's also good math to keep in mind while car shopping.

Of course, if you're car shopping, it's good to remember that gas mileage also depends on how you drive and where you drive. Some hybrid models get better efficiency in city driving than on highways, for example, while conventional vehicles get better mileage on the highway.

On the interstate, my 10-year-old Honda Civic gets the same mileage as our 1-year-old hybrid. Of course, the Civic has the fuel-economy advantage of being smaller and lighter.

Sometimes people get better-than-advertised fuel economy, sometimes they get worse. The fuel ratings are more complicated for hybrids like our C-Max, because when you drive it just right, it runs on the electric motor and doesn't use any gas.

In my case, the good news was that Ford sent me those two checks - enough money to cover the dif-ference between advertised and revised fuel economy for nearly seven years.

By my math, another $514 and we would be even.

Contact David Slade at 937-5552.