1. Airflow gadgets -- $90+ wasted
The Theory: High-tech devices designed to increase your engine's airflow will improve fuel efficiency.
The Facts: It sounds plausible, but the results don't back up the impressive claims. Consumer Reports tested several of the devices, such as Fuel Genie ($89.95, plus shipping), that purport to increase fuel economy by accelerating airflow to the engine. The tests found no noticeable gains in MPGs, despite claims of 50% fuel savings. While it's true that drastically increasing the airflow to an engine is a common way to increase horsepower (i.e. forced induction through turbo and superchargers), doing so will actually increase fuel consumption and increase wear on the engine, not to mention that this proven technology costs significantly more than its gimmicky competition.
2. Fuel additives -- $5 to $250 wasted (per treatment)
The Theory: The gas we buy can be improved by adding scientifically formulated chemicals that will increase fuel efficiency and, sometimes, horsepower.
The Facts: Clearly, some drivers believe the answer to their fuel woes lies in a magic elixir, because there are numerous fuel treatments that claim to increase MPGs, despite no scientific proof or explanation of how less fuel is burned. According to CNN.com, one common tactic used by shady fuel-additive makers is to tout the product's approval by the Environmental Protection Agency (EPA). This suggests that a trusted consumer watchdog has approved the product's claims, but in fact, the EPA had only deemed that the product does not increase a vehicle's harmful emissions. The truth is, if there were an additive that made fuel burn more efficiently, oil companies would be racing to market their new gas at the pumps and gain a bigger market share.
3. Premium fuel -- $4 wasted per tank (on average)
The Theory: Premium gas provides increased performance and better gas mileage.
The Facts: This is true ... if you own a premium automobile that requires high-octane gas, but these cars make up the minority of daily drivers. So if you're in the majority -- drooling over Ferraris from the seat of your Corolla -- your car's engine control unit (ECU) is programmed to run on the octane levels present in regular gas. Increasing the octane -- either through buying premium gas or adding bottles of octane-boost -- can actually cause the engine to be less efficient, as the car's combustion timing becomes altered and efficiency is lost. But the most noticeable loss will be the extra 20 cents per gallon you'll be wasting to buy high-octane gas. A safe bet is that if you can afford a vehicle that requires only premium fuel, you likely aren't concerned with gas prices or tracking mileage.
4. Over-inflated tires -- $200 wasted (minimum)
The Theory: Rounder tires roll easier, creating less work for the engine and therefore, better MPG.
The Facts: Again, this tip is true ... to a point. Over inflated tires will have less friction with the road, which lessens the effort the engine exerts to keep the car rolling, providing slight gas savings. However, overinflated tires will wear out quickly and irregularly, causing you to need early replacements at a cost of about $50 to $100 per tire. What's worse is that the decreased contact with the road increases stopping distances and limits handling capabilities. This all adds up to a large risk in costly accidents and injuries. Even if you are lucky and avoid a collision, it would take a lifetime (which could very well be short if you're riding on bald and bulbous tires) for your fuel savings to negate the cost of four new tires. According to Edmunds.com's testing, the fuel consumption difference between driving with over-inflated tires and tires at the recommended pressure is negligible. Sometimes, despite what GM's recent track record suggests, carmakers do know what they're doing and the recommended settings and levels do provide the best results.
5. Roll down windows rather than using air conditioning -- comfort wasted
The Theory: Operating the AC to cool the vehicle uses fuel, so it's more efficient to cool off by driving with the windows down.
The Facts: While it's true that some fuel is used to operate the AC compressor, as much or more fuel is lost when the windows are down. Rolling down the windows increases the drag on the car, which causes the car to work harder to maintain its speed. For even better mileage, you can improve your AC's efficiency by using the re-circulation setting on the car's HVAC system instead of forcing the AC to cool the hot air from outside. Heeding this tip will increase your mileage, as well as your comfort.
The Bottom Line
The act of saving gas borders on sport for some thrifty drivers, but extreme measures don't always equal extreme savings. And while some gas-saving methods will offer a few cents per tank in savings, the safety concerns of these methods outweigh any benefits to your bank balance. It's a boring realization, but the real road to fuel savings lies in common-sense approaches like avoiding unnecessary driving and idling, driving the speed limit and performing regular vehicle maintenance. You won't amaze anyone with this practical approach, but it's better than shocking people with useless purchases, a battered car and a wind-swept hairdo.
(Sumber artikel: http://financiallyfit.yahoo.com/finance/article-112573-9379-1-5-driving-myths-that-cost-you-money?ywaad=ad0035&nc )