Fuel efficiency can be a difficult metric to track, as the difference between 38 miles per gallon and 40 miles per gallon isn't exactly obvious to most drivers. While those extra few miles per gallon could save drivers hundreds of dollars over time, most just assume that the rating given to the car will be the same for the life of the vehicle.

In reality, the EPA fuel economy ratings are actually just estimates. Driving style and the condition of the car can have major effects on fuel economy, but most drivers will likely not notice this. If you've been hitting the gas station more often than you would like to, however, it's possible that doing a little maintenance work could help you improve your fuel economy - and save you money in the long run.

If you really feel like you've been going to the gas station on a very frequent basis, the first potential culprit you should investigate is the oxygen sensor. Modern vehicles with electronic fuel injection systems need to ensure that the car has the right mixture of oxygen and fuel. If the oxygen sensor is faulty or not working correctly, however, the car could be giving your engine way more fuel than it actually needs.

According to the Department of Energy, this part causes the biggest swings in fuel economy from a mechanical perspective. Fixing your oxygen sensor could improve your fuel economy by as much as 40 percent. Thus, it should be a priority every time you take your car into the shop or work on it yourself. Nobody wants their 40 MPG compact to suddenly drop down to 26 MPGs just because they have been lax on their maintenance. In most cases, repairing an oxygen sensor will pay for itself. Even if the oxygen sensor is not at fault, it pays to look at the fuel-injection system in general, including any sensors in the actual gas tank, as any one of these parts not working properly can kill efficiency.

Regular tune-ups can also help improve your fuel economy. Essentially a tune-up will eliminate any inefficiencies in your car's emissions system, which will reduce the amount of fuel you have to use. This is more of a minor boost in efficiency, but repairing an engine that is really out of tune can improve MPGs by approximately 4 percent, according to the news source.

Tune-ups are among the easiest forms of maintenance for amateur mechanics to perform on their own, but while you're working on the car, you might want to take a minute to look at the tires. The tires are ultimately where the car meets the road, and thus they're extremely important for efficiency. The news source says that inflating tires that are looking a bit flat can improve MPGs by approximately 3.3 percent. Remember, do not use the pressure printed on the side of tire - this is the maximum psi allowed by the tire manufacturer. The recommended pressure for your car should be located within the owner's manual or on a sticker attached to the inside of the door.

The last recommendation is minor overall, but can still have a slight impact on fuel efficiency. Some drivers like to use a different recommended grade of motor oil for their car for whatever reason, whether it be temperature or overall viscosity. However, doing so can actually have harmful effects on your MPGs - usually about 1 to 2 percent. Switching back to the recommended type of oil will thus improve the engine's efficiency and leave you with a bit more money in your wallet.