WITH THE COST of gas surpassing $4 a gallon, the prospect of embarking on an affordable family road trip has gotten a lot more daunting.

To help you avoid spending the majority of your vacation fund on fuel this summer, make sure your car is operating at peak fuel efficiency.

"There is no magic bullet for increasing your fuel economy," says Tony Molla, spokesperson for the National Institute for Automotive Service Excellence (ASE). "It's the combination of things that you do that will get you the best value of the gasoline you're buying."

The good news is that most of the things you can do are easy and affordable. Here are five inexpensive ways to make your car more fuel-efficient.

1) Ease off the gas pedal

Even if you use all the gas-saving tips in the book, you'll still waste gas if you don t lighten up your lead foot.

Driving aggressively think speeding, rapid acceleration and braking can lower your gas mileage by as much as 33%, wasting anywhere from 20 cents to $1.35 per gallon, according to the Department of Energy (DOE).

Keep in mind that cars are most fuel efficient when you're driving at around 55 miles per hour, says Jeff Bartlett, deputy editor online for ConsumerReports.org. According to a recent ConsumerReports.org study, when a Toyota Camry's speed increased to 65 miles per hour (mph) from 55, its fuel economy dropped by 5 miles per gallon (mpg). Another thing to consider: Chances are your pedal to the metal driving will leave you with costly speeding tickets. (Read our story.

One easy tip: Next time you hit the highway for a long drive, shift into cruise control, which "can be an effortless way to get more fuel economy," says Bartlett.

Read our story for more ways to reap gas savings.

2) Change Your Air Filter

A car's air filter prevents dirt and other matter from entering the engine's cylinders, where they can cause mechanical wear and hurt your car's performance.

Replacing a clogged air filter (on your own) costs around $20 and can improve your car's gas mileage by up to 10%, according to the DOE, leaving you with savings of up to 41 cents per gallon.

3) Properly Inflate Your Tires

"If you're driving around with underinflated tires you're using more fuel than you need to," says ASE's Molla. Keeping the right amount of air in your tires, improves gas mileage by around 3.3%, helping you save up to 12 cents per gallon of gas, according to the DOE.

Ideally, you should check your tire pressure at least once a month when your car has sat for at least one hour and the tires are cool, according to ConsumerReports.org. To find the proper tire pressure, look for a yellow or white sticker on either the driver's door jam or the inside of the door, which includes the tire pressure specification in pounds per square inch (psi), says Philip Reed, senior consumer advice editor at Edmunds.com. Most owners' manuals also state where to look on your car to find the recommended pressure.

Click here for other ways to save on gas.

4) Stick to the Right Oil

You may not be able to tell the difference by looking at it, but using the right type of oil can really help improve your car's fuel efficiency. According to the DOE, using the right oil can boost a car's gas mileage by up to 3%, saving you up to 12 cents per gallon.

To find out what grade of motor oil works best with your car, check the owner's manual, or - if you have a relatively new model - check the gas cap. "You don t want to go any lighter than what's recommend by the manufacturer because that could damage the engine and repairs would get costly," says Christie Hyde, a spokesperson for AAA.

Also, don't forget to change your oil regularly. Among other things, an oil change cools the car's engine and helps it run smoothly. Change your oil either every three months or 3,000 miles, whichever comes second, says Molla. Otherwise, your engine could start having problems or, even worse, break down.

5) Lighten the Load

One of the easiest ways to improve your car's fuel efficiency is by removing any excess weight. "If you're the person who always keeps the golf clubs in your car just because you may stop by the range, you're wasting gas," says AAA's Hyde.

According to the DOE, an extra 100 pounds inside your car can reduce its mileage per gallon (mpg) by up to 2%. Lighten your load and you'll save four to eight cents per gallon.

The car's roof rack can also weigh you down. A loaded roof rack can decrease fuel economy by 5%, according to the DOE. "[It] can really kill your fuel economy especially [on] highway travel," says Hyde. "It can dramatically increase the aerodynamic drag on the vehicle and cause your fuel efficiency to plummet."

If possible, try to put your luggage or fishing and camping gear inside the car.

Click here for more on lightening your load.

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