Hunting Happiness

CNN has an interesting article about myths that purport to but don’t actually save gas.  Much of it is “borrowed” from this Consumer Reports article.

1. Filling up in the morning.  The theory is that the metering mechanism in pumps is calibrated for around 70F and temperatures in the morning have been lower overnight and therefore the gas is likely to be more dense.  CR says there is very little temperature variance at the nozzle and therefore no measurable gain in filling up in the morning.
2. Air conditioning (or the non-use thereof).  CR talks about this and Myth Busters has also tested it.  Logic suggest that low driving speeds may see some MPG benefit to rolling down the windows and turning off the A/C.  As speed increases, wind resistance increases exponentially and logically the windows being down would eventually increase drag to offset the MPG savings of having the A/C off.  If you believe CR the differences are so minor that it’s not worth debating over, and since A/C will be more comfortable it’s the clear choice.
3. Dirty Air filters kill MPG.  Apparently modern cars have computers that are smart enough to detect decreased air flow and adjust the air-fuel mixture appropriately.  The net effect may be less horsepower, but not less MPG.
4. Tire pressure.  All sources agree that tire underinflation definitely hurts MPG.  Some of the hyper-miler online forums advocate raising tire pressure above the manufacturer’s maximum to the tires’ sidewall maximum, or even higher.  This would raise MPG slightly due to less tire on the road.  Having less tire on the road will also affect braking and handling performance, and could conceivably throw off ABS and vehicle stability control mechanisms.   A better solution would be to switch to low rolling resistance tires which can save 1-2 MPG according to CR.

With gas prices high, it is tempting to go to extremes to conserve gas.  However, it is important to keep in mind that some savers are really just myths, and that some techniques could even be dangerous.