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Saturday, April 22, 2006


Mileage tips

I've dedicated a lot of blogging to gas mileage devices that don't work. This time, I'll pass on a few tips about gas mileage that might actually work. However, I would like to start with a few words of caution. Not all of these tips might work for all cars, and there are some scammers that have been known to take up one or two of these principles and use it for dubious ends. In some cases, the mileage gain may be so tiny as to be unmeasurable. All that I can promise is that the theories behind them are sound and BS-free. Here are some tactics that might save you some gas. I don't have anything here where you can get a $69.95 part, install it in a few minutes, and improve your milage by 25%, but I don't believe anyone who actually claims that, either. These tips either make only minor improvements, or require heavy wrenching and starting with an older car that gets pretty bad mileage as it is.

1. Keep you car in good working order.

If you have worn spark plugs, a failing oxygen sensor, or other problems, your car probably won't get its best gas mileage.

2. Check the tires.

Low pressure is the biggest one. If you pump them up to the maximum allowable pressure - as indicated on the tires, not what's recommended in the owner's manual - you will cut down on friction. Some people will tell you this may screw up the ride or handling. The ride will be harsher, but it's not likely to ruin the handling. Many street tires deliver maximum grip when inflated well beyond recommended pressures anyway. I've raced on tires inflated to 40 psi - not that you should drive with your tires inflated like this on the street, but I have to say it didn't give my car any treacherous handling quirks. Be careful if you pump up the tires to the maximum pressure on the sidewall when they're cold, though, as the pressure increases when they heat up.

If you're in the market for new tires, consider ones meant for low rolling resistance. These will cut down on friction a little.

3. Good lubricants.

Different oils produce different amounts of friction. The thinner the oil, the less friction, so using the thinnest grade of oil your owner's manual recommends for you climate can help out. Look for API's "Energy Conserving" or "Energy Conserving II" symbol - oil manufacturers can't legally use this unless they have demonstrated to the American Petroleum Institute that their oil can improve gas mileage compared to oils without this mark. Some brands of oil seem to produce less friction for their oil weight - I've heard reports of Mobile One and Royal Purple being especially good, and there may be others. It's possible to verify that an oil produces less friction by testing it on a dyno - less friction means more horsepower. And don't forget transmission and differential oils, too.

Of course, there are plenty of people selling snake oil here, no pun intended. After all, it's hard to tell by looking whether it will cut down on friction, and as I've noted before, mileage is variable enough that it can be hard to measure. In particular, I would recommend avoiding anything containing PTFE (Teflon).

4. Underdrive pulleys.

These are often used by enthusiasts to send less power to things like the air conditioning, power steering, and alternator. This is usually done to free up horsepower to drive the wheels, but it should be capable of improving mileage too.

5. Updating an older car.

Sometimes you can newer technology to an older (usually pre-'90s) car and improve your fuel economy. Most American smallblock V8's had their cylinder heads redesigned in the '80s and '90s for more efficiency, and you can add fuel injection to carbureted cars. This mods are admittedly a little more "expert" than most...

6. Drive more gently and less often.

Driving strategies are the least glamorous thing, but often the most effective. Less pedal to the metal driving, combining errands into one trip, and letting the car coast can all save plenty of gas. One note about coasting: Many modern cars are designed to shut off fuel entirely if the car is in gear, the engine is above a certain RPM, and your foot is off the accelerator (and clutch, if you have a stick-shift). You can use this to your advantage by coasting down hills, and even by building up some speed and letting the car coast for a while. One guy on the Grassroots Motorsports board claimed he'd boosted his Ford Focus's mileage from 25 mpg to 33 by changing his driving alone, although there's no telling just how crazy his "before" driving was.

This is a great idea for a post. Thanks.

Have you crunched the numbers on driving to Venezuela to fill up with their .15 a gallon yet? I bet it's starting to get pretty close to breaking even.
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