Although there are some studies that do not confirm the following, there are also studies that do...
Three pragmatic and cost-effective ways to improve your gas mileage, reducing the money you spend on fuel and the negative effect on the environment are:
1) Oil - there is evidence that synthetic oil is much more "slippery" than conventional oils and will help improve your gas mileage. I have used synthetic oil in various gasoline and diesel powered cars over the last fifteen years and will attest that synthetic oil flow much better and maintains viscosity at temperature extremes. Most manufacturers will allow you to lengthen the period between oil changes if you use synthetic oil.
The combined effect of better mileage, reduced wear on your engine and increased periods between oil changes can have a very positive effect on the planet, and possibly your finances.
2) I was watching an episode of driving television yesterday that quoted a Canadian government website as saying that a dirty and clogged air filter can reduce your gas mileage by as much as ten percent. The reason for their claim was that it takes as much as 10,000 litres of air to burn 1 litre of fuel, and that anything restricting the flow of air affects efficiency. I have found websites claiming that air filter have no effect and some saying they do... I travel on dirt roads, and keep fanatical track of my mileage. I have noticed that I tend to achieve my best mileage in the months after I have changed my air filter.
3) If you are in need of new tires, there are many makes of tires available for all types of cars that can achieve four to seven percent better mileage. They do this by having less rolling resistance (can be a combination of stiffer sidewalls and/or different rubber compounds). These tires are generally more expensive to acquire, but if one does the math, especially with the fuel prices we are seeing, these tires more than pay for themselves, and will result in your vehicle achieving better mileage, burning less fuel, all other factors being equal.
Here are three websites with more tips on how to attain better mileage:
Chris Smith CSSBB
Chay Realty Inc., Brokerage