9. Gas up in the morning: This myth is based on the science that gas is denser when it is cool out than in the heat of the day. The logic goes that purchasing gas in the morning, when it is cool, will mean you get more in your tank than if you buy it in the heat of the afternoon, because gas pumps measure volume and not density of the fuel. The problem is that the gas is stored in underground tanks, so the heat of the day has little effect on the gas temperature, meaning you can purchase gas at any time and get virtually the same amount.
But there is one reason you might want to buy gas in the morning. If you believe gas prices are going to be rising, most gas stations don't change their daily price until 8 a.m. or so, meaning you still can get the previous day's price in the early morning.
10. Overinflated tires will save gas: The logic is that if underinflated tires waste gas and properly inflated tires get better mileage because of less tread contact on the road, over inflated tires would have even less tread contact, which would increase mileage. Popular Mechanics tested this theory and found that it didn't provide any added benefit and that it was dangerous.
Increasing your fuel efficiency as much as possible is sensible, but make sure that you don't buy into the myths that can be dangerous and siphon your wallet.