It's often said that keeping your car well maintained will get you better gas mileage, but some steps have a quicker payback than others. The government's fuel economy website has a rundown of the usual checklist and the savings you can expect—if your car needs the maintenance—at the current average gasoline price of $3.23 per gallon.
An engine tuneup, for example, could enhance an out-of-tune car's mileage by 4 percent, or the equivalent of about 13 cents per gallon. But my neighborhood mechanic says the cost of a tuneup for our old 1994 Saturn would be about $300. We'd earn back that cash outlay only after purchasing more than 2,300 gallons of gasoline at today's prices. And since our car gets about 27 mpg, we'd have to drive 64,000 miles. I don't think that car, which already has nearly 100,000 miles on it, will make it that far. If we found a mechanic who could do a tuneup for about $100, then it would take a little over a year and a half—assuming we drove about 12,500 miles per year.
However, replacing a clogged air filter has almost an immediate payback at today's gasoline prices. The government studies show that's like saving up to 32 cents per gallon, and air filters for many models can be bought for $20 or less. You'd have to buy only about 60 gallons of gasoline to break even on the investment in a new air filter, if you need one.