How does Greentech works?  
Greentech Fuel Saving Device applies the newest Molecule Enhance Technology with is developed by Moletech International Limited and Taipei Medical University. It includes the Fuel Molecule Enhancer and Air Refining Device. It can be fitted into all kinds of the vehicle and it does not affect the vehicle warranty because there is no modification work on the vehicle.
Greentech Fuel Saving Device was initially developed to decrease harmful exhaust pollutants. Over the past seven years, we have tested hundred of vehicles and found that those using our fuel saving device not only emitted less harmful exhaust, but also gained more miles per gallon. In addition many vehicle owners have reported a rise in horsepower and a smoother running engine after using our fuel saver. We double checked our results by sending our fuel saving device to California CEE (USA EPA & CARB certified testing center), TUV Rheinland Group, and SGS, all of whom verified and supported our research and development data.
  Drive more efficiently  

Drive Sensibly (5-33%)
Aggressive driving (speeding, rapid acceleration and braking) will waste gas. It can lower your gas mileage by 33 percent at highway speeds and by 5 percent around town. Sensible driving is also safer for everyone.

Observe the Speed Limit (7-23%)
While each vehicle reaches its optimal fuel economy at a different speed (or range of speeds), gas mileage usually decreases rapidly at speeds above 60 mph. Observing the speed limit is also safer.
Remove Excess Weight (1-3%)
Avoid keeping unnecessary items in your vehicle, especially heavy ones. An extra 100 pounds in your vehicle could reduce your MPG by up to 2 percent. The reduction is based on the percentage of extra weight relative to the vehicle's weight and affects smaller vehicles more than larger ones.
Avoid Excessive Idling
Idling gets 0 miles per gallon. Cars with larger engines typically waste more gas at idle than do cars with smaller engines.
Use Cruise Control
Using cruise control on the highway helps you maintain a constant speed and, in most cases, will save gas.
Use Overdrive Gears
When you use overdrive gearing, your car's engine speed goes down. This saves gas and reduces engine wear.
  Keep your car in shape  

Keep Your Engine Properly Tuned (4%)
Fixing a car that is noticeably out of tune or has failed an emissions test can improve its gas mileage by an average of 4 percent, though results vary based on the kind of repair and how well it is done.
Fixing a serious maintenance problem, such as a faulty oxygen sensor, can improve your mileage by as much as 40 percent.

Keep Tires Properly Inflated (up to 3%)
You can improve your gas mileage by around 3.3 percent by keeping your tires inflated to the proper pressure. Under-inflated tires can lower gas mileage by 0.3 percent for every 1 psi drop in pressure of all four tires. Properly inflated tires are safer and last longer.
The proper tire pressure for your vehicle is usually found on a sticker in the driver's side door jamb or the glove box and in your owner's manual. Do not use the maximum pressure printed on the tire's sidewall.
Use the Recommended Grade of Motor Oil (1-3%)
You can improve your gas mileage by 1-2 percent by sing the manufacturer's recommended grade of motor oil. For example, using 10W-30 motor oil in an engine designed to use 5W-30 can lower your gas mileage by 1-2 percent. Using 5W-30 in an engine designed for 5W-20 can lower your gas mileage by 1-1.5 percent. Also, look for motor oil that says “Energy Conserving” on the API performance symbol to be sure it contains friction-reducing additives.
Replacing a Clogged Air Filter on Modern Cars Improves Performance but Not MPG
A new study shows that replacing a clogged air filter on cars with fuel-injected, computer-controlled gasoline engines does not improve fuel economy but it can improve acceleration time by around 6 to 11 percent. This kind of engine is prevalent on most gasoline cars manufactured from the early 1980s onward.
Tests suggest that replacing a clogged air filter on an older car with a carbureted engine may improve fuel economy 2 to 6 percent under normal replacement conditions or up to 14 percent if the filter is so clogged that it significantly affects drivability.