4. Improves gas mileage. Poor engine lubrication can lead to increased fuel consumption, so make sure there is enough clean oil in the engine. The U.S. Department of Energy says that with routine changes and the right kind of oil, gas mileage can be improved over time by 1-2%. That doesn’t sound like much of an improvement, but for the average car, it leads to savings of an entire gallon of gas for a year!