Biodiesel pump (© Propel)Click to enlarge picture

Biodiesel, created from vegetable oils including canola, is often blended with petroleum diesel at the pump, and can be burned in any diesel engine.

1. Easy on the Throttle
The single most important technique to make your existing car more efficient is speed, or lack thereof. In the city, avoid jackrabbit starts and lead-footed stops — this kills your fuel economy as well as your brakes. On the highway wind resistance is your enemy, and the faster you go the tougher the battle. When Consumer Reports researchers increased the speed of a 4-cylinder Camry test car from 55 to 65 mph, the average highway fuel economy dropped from 40 mpg to 35.

2. Trading Pounds for Gallons
Lighter cars get better fuel economy. But before trying to cut your car’s weight and drag by tearing out upholstery and knocking off side mirrors, do the easy stuff first. Jettison the sandbags, golf clubs, and phonebooks from the trunk (better keep that spare, though). An unused roof rack also creates unnecessary drag. Also, don’t waste your gas dollars driving to stores that are closed, or getting lost on the way. Map out routes beforehand, call ahead or check hours online, use a GPS system, or combine trips to drive fewer total miles.

3. Sun Block
Smart solutions are sometimes the simplest. Sun reflectors will keep cabin temperature down while the car is parked, easing the load on the AC when you return. Lower temperatures will soften the sting on your wallet as well as on the sensitive flesh next to it. Research has also found that extreme summer heat can cause more air pollutants such as volatile organic compounds to be released from upholstery, plastics and other components, so reflecting the sun can be good for your health, too.

4. Better Breathing
Spending a minute on cabin air quality can save gas and protect your lungs from airborne gunk. Interior cabin air filters — which remove particles pumped in by your car’s ventilation system — clog over time, removing fewer particles and cutting into your overall MPG by reducing the efficiency of the air conditioner. Most automakers suggest replacement every 15,000 miles. A multistage, activated charcoal filter for a Ford Taurus costs just $34 ($24 for a Toyota Prius), and many can be replaced in just a few minutes.

5. Tune -Up
A clean-running engine will not only use less fuel, but will pump fewer emissions out the tailpipe. Take your car for its regular maintenance and oil changes. High-quality synthetic oil of the right grade can prolong the life of an engine and help it get better fuel economy as well. Rotating tires at designated intervals will keep them wearing evenly and lasting longer.

6. High-MPG Tires
Another no-brainer is tire inflation: Keeping your car’s tires at the maximum recommended pressure (printed in the owner’s manual) will help maintain your optimal MPG and tire life. According to Consumer Reports, a tire’s rolling resistance “can add or detract an additional one or two miles per gallon,” which adds up over time. You may also want to investigate replacement tires that claim low rolling resistance and high fuel economy, such as Michelin’s Energy MXV4 and Continental’s ContiPremierContact.

7. Veggie Out
If you prefer the smell of French fries and Thai food over diesel fumes, then vegetable-based fuels might be your ride. Any diesel engine can burn biodiesel without modification, and a growing number of locations around the country now offer biodiesel at the pump. However, make sure the biodiesel you choose is within the recommended grade for your engine, otherwise you risk voiding the OEM warranty for the vehicle. If you’d rather not pay for your fuel at all, a conversion kit will let a diesel car or truck run on vegetable oil. Once filtered, the oil will burn in a diesel engine like regular fuel, only with a home-cooked smell and no net carbon emissions.

8. Solarize Your Roof
Existing solar cars tend to look like recumbent bicycles wrapped in black trash bags, and they also don’t have much to offer on cloudy days. But that doesn’t mean you can’t put the sun to work for your commute. Solar Electric Vehicles manufactures solar panel systems that can be installed on the roof of your hybrid. Gathering sunlight and converting it into electricity, the panel lets a hybrid run for up to 20 miles per day in pure electric mode, netting a purported 29 percent increase in fuel economy.

Do you have any easy tips for cleaner and greener driving?

9. Plug It In
Don’t want to wait for car companies to sell you the next generation of hybrids? While General Motors and Toyota talk about plug-in hybrid cars, conversion kits are already here. By adding a beefed-up battery pack and some extra computing power, a Prius or Escape Hybrid can be plugged into a home socket. Fully charged, they will run on electric power alone for up to 40 miles — more than enough for the average commute. These kits aren’t cheap, though. Massachusetts-based Hymotion is taking orders now for its kit, which starts at $10,000.

10. The Un-Car
The ultimate green car upgrade might be no car at all (or at least not driving the one you have). If paying for another fill-up sounds about as pleasurable as a carjacking, take a look at the alternatives. Car-sharing companies such as Zipcar let you have a car only when you need one. Pay by the month, sign up online, swipe your card and off you go. Gas, insurance, and air fresheners are already taken care of.

Jacob Gordon is a freelance writer, a blogger for TreeHugger.com and a producer of TreeHugger Radio. He can be reached at jacob@treehugger.com.

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