Being smart about your fuel use is guaranteed to save you green. By Jessica L. Anderson, Associate Editor August 1, 2011 1. Never (fill up) on a Sunday. Or a Friday or Saturday, for that matter. Gas prices typically rise over the weekend; most station owners post the new prices Thursday mornings by 10 a.m. To find the best price near you no matter what day it is, download the free GasBuddy app to your Android phone or iPhone and search by proximity or lowest price. (If you don’t have a smart phone, log on to GasBuddy.com before you leave the house.)2. Take a tip from hyper-milers. For these True Believers, fuel economy is a mission. Among their strategies: Inflate your tires to the maximum pressure recommended by the tire manufacturer. You can improve your mileage by as much as 10%, and the only trade-offs are a slightly harsher ride and a bit more noise. Baby your brakes -- coast whenever possible, and conserve momentum in stop-and-go traffic. If you’re sitting in traffic, turn your engine off. Ditch the junk in your trunk; every 100 pounds reduces your mileage by 2%. To reduce drag, keep windows and sunroofs closed at highway speeds and get rid of the roof rack. 3. Don’t spin your wheels. Instead of getting stuck in a traffic jam, map out your route ahead of time. Traffic.com has live traffic maps for metro areas across the country that let you check the roads you’ll take, or you can enter your destination and ask for the best route to take. On the go? The free Google Maps app for Androids and iPhones displays area roads in red, yellow or green, depending on how congested they are. If you use the navigation feature, the app will automatically direct you around traffic. See our article on 10 Free Travel Apps for Your Road Trip for more ways to let technology save you time and money. 4. Get E-ZPass. Cruise through the tollbooth instead of idling in long lines to fork over cash. The pass is good from Maine to Virginia and as far west as Illinois. Here’s how it works: When you purchase your pass, you preload the account. Then each time you pass through a booth, a scanner reads your pass and deducts the amount of the toll. The required minimum balance varies from state to state; some states levy monthly fees, and a few, such as New Jersey and New York, offer commuter discounts. You’re not required to buy your pass from your home state, so check surrounding states’ Web sites to see which has the cheapest plan for you (see links to each state’s program). Advertisement 5. Use a gas cash-back credit card. Earn up to a 5% rebate when you use a branded credit card, such as the BP Visa Card. The BP card doubles your rebate for the first 60 days, and offers 2% on travel and restaurant purchases and 1% on most other purchases. 6. What doesn’t work. A dirty air filter might once have dinged your mileage, but modern engines regulate air intake with computers, so changing the filter won’t help. And don’t worry about filling up at a cooler time of day to avoid gas evaporation -- the temperature of the gas coming out of the pump changes very little. Most important, unless your manual says “premium gas required,” you may use a lower grade. You might experience slightly slower acceleration, but knocking is a thing of the past, thanks to engine knock control systems.