While the average American still replaces his or her car every three years, there's plenty of reasons to hold onto the keys a lot longer. Modern cars are built to last well beyond 100,000 miles, if properly maintained, and can cost very little in maintenance and repairs over that period.

Whether finances are tight or you just aren't ready to get a new set of wheels, follow these four tips to help ensure your used car lasts longer without expensive repairs.

Stay on schedule: All cars require regular maintenance, and you'll make an old car last longer if you stay on top of the manufacturer's recommendations. Follow the maintenance schedule that's listed in your owner's manual to keep your used car in tiptop shape. For most drivers, it's not necessary to increase the frequency of the maintenance (such as more frequent oil changes). Nor is it critical to have other services performed that are not on the manufacturer's list of recommendations for that specific mileage. Doing either is often a waste of money.

Give it a once-over: At least once a week, spend a few minutes walking all the way around the car to make sure all the lights and turn signals are working. Check the tires for uneven wear and other damage. Lift the hood, checking the battery connections for corrosion and the hoses for cracks or wear. Check the fluid levels.

Watch the tires: Your car's tires are the only part of your car that actually touches the ground, and those four patches of rubber need to be in top-notch shape in order to provide optimum safety as well as fuel economy. In addition to inspecting tires regularly, check tire pressure once a month and add air as necessary. The proper tire pressure (written in pounds per square inch, or psi) is listed in the car owner's manual as well as on a label on the driver's side doorjamb. Maintaining proper tire pressure will help prevent issues that could require expensive repairs, such as excessive wear on suspension components or blowouts that can result in accidents. It will also help your fuel economy -- a nice bonus with today's rising gas prices.

Drive wisely: Your driving style can affect an old car's life span. Leaving a traffic light like you're in a race, jamming on the brakes at a stop sign and taking turns at high speed are all very hard on your car's engine, brakes, tires and suspension system. This type of driving can lead to excessive wear and tear on these parts of your used car, requiring pricey repairs or replacement. While you don't need to drive like an old lady, taking a bit more care will help increase the life span of your car without expensive repairs that hurt your wallet.