Maintenance

A poorly maintained or malfunctioning car can release as much as 100 times the pollution of a well-maintained car. Almost half your tank of gas can be used up simply by abusing or neglecting your vehicle. You could pocket over $600 a year. Having a trusted mechanic check your vehicle on regularly scheduled intervals helps your car to maintain its efficiency.

Oil

Changing your oil on a regular basis and using good engine oil, preferably synthetic or standard oil treated with a friction reducing oil additive can improve fuel economy by as much as 12%.
Consider using low-viscosity motor oil. This lubricates the moving parts of the engine better than ordinary oils, which reduces friction. The best oils can reduce CO2 emissions by more than 2.5%

Air Filters

The filters are part of the air intake system that adds O2 to the engine for combustion. An air filter that is clogged with dirt, dust or bugs chokes the flow resulting in more fuel being burned to compensate. Replacing a clogged air filter can reduce fuel consumption. If you drive in a lot of stop and go traffic, air filters should be changed more frequently.

Tire Pressure

Under-inflated tires mean there is less surface area in contact with the road as your tire is riding on the side walls more than optimizing the whole surface tread. For every 2 pounds per square inch (psi) your tire is under inflated, you are decreasing fuel efficiency by 1%.   Check your tire pressure once a month. The recommended psi for your tires is usually located on the driver’s side door.