Myth or Fact?

When the Alliance to Save Energy conducted consumer market research to guide the Drive $marter Challenge campaign, drivers raised a number of common gas and fuel-efficiency questions and myths: "I heard I am supposed to fill up my tank in the morning." "It takes more fuel to restart a car than to idle." Is this true? They were clearly interested in accurate information for their decision-making. Sometimes it seems hard to come by.

For the information below, we have gone to Consumer Reports, which has conducted recent vehicle testing, and then for further information and clarification, directly contacted David Champion, Senior Director of the Auto Test Center at the Consumers Union, the publisher of Consumer Reports. We also went to our campaign partners, the U.S. Environmental Protection Agency (EPA), and the American Petroleum Institute (API), which supplied answers on gas-related questions.

Dispelling idling myths, Consumer Reports recently conducted vehicle testing and reported results in its June 2008 issue on the following myths:

Myth: It is better to let your vehicle idle than turn the engine off – turning the engine back on uses more fuel than idling.

Fact: Idling uses more fuel than turning off your engine and restarting it. As a rule of thumb, turn off your engine if you will be idling for more than 30 seconds. David Champion, Senior Director of Auto Testing for Consumer Reports, told the Alliance to Save Energy, "You should not turn your engine off at a traffic light. However, if you are stuck at a train crossing or bridge opening, and it is likely you are going to be parked for a number of minutes, you should turn off your engine."

Myth: You should warm up your vehicle in the morning before driving.

Fact: Engines warm up faster, and are more fuel-efficient, when on the road.

Myth or Fact? There is no rhyme or reason to why gas prices fluctuate.

Fact: According to the Energy Information Administration’s Primer on Gasoline Prices, "Even when crude oil prices are stable, gasoline prices fluctuate due to seasonal demand and local retail station competition. Gasoline prices can change rapidly if something disrupts the supply of crude oil or if there are problems at refineries or with delivery pipelines."

Myth or Fact? Gas prices are higher in the summer.

Fact: According to API, so many factors influence gasoline prices that a seasonal pattern is not obvious. However, two important factors do put upward pressure on prices in the summertime every year: 1) Summertime is driving season or peak demand in the United States. 2) Gasoline formulated for summer weather is more expensive to make.

Myth: Warmer gasoline expands, while cooler gasoline is denser. Since gasoline is priced by the gallon, buying gas when ground temperatures are cooler means more BTUs per gallon.

Fact: According to Consumer Reports, the temperature of gasoline, as it is being pumped from underground tanks into your vehicle, changes very little, if any, during the course of the day. Any more gas you may obtain is negligible.

Myth or Fact? More gasoline is lost through evaporation when refueling in a 90° F state, compared to a state with temperatures in the 70° F range.

Fact: According to David Champion, Senior Director of Auto Testing for Consumer Reports, gas evaporation during refueling is least during the coolest times of the day. However, with modern fuel pumps, any loss is negligible. In the summer, a decrease in fuel-efficiency may be attributed to another source. According to the EPA in certain high-ozone areas, the EPA mandates the use of special reformulated gasoline (RFG) during the summer months. RFG causes a small decrease (1-3%) in a vehicle’s fuel economy compared to conventional gasoline. However, it is also less conducive to evaporation than regular gas.

Myth: Fill your tank when it is half full in order to minimize gas evaporation and loss.

Fact: According to API, technical changes to vehicle fuel systems have virtually eliminated fuel evaporation loss.

Myth or Fact? Park in the shade; heat from the sun will result in fuel evaporation and loss.

Fact: According to API, technical changes to vehicle fuel systems have virtually eliminated fuel evaporation loss. David Champion, Senior Director of Auto Testing for Consumer Reports, told the Alliance to Save Energy that a small amount of gas does evaporate from older vehicles (1974 or older). According to the EPA, avoid poorly fitted or missing gas caps to decrease evaporation loss.

Myth or Fact? It is more fuel-efficient to turn on a car’s air conditioner (AC) and close the windows.

Fact: According to David Champion, Senior Director of Auto Testing for Consumer Reports, in the city, turning off the AC and opening the windows saves about 1 mpg. However on the highway, the difference between windows and AC on a vehicle’s fuel economy is negligible. According to Consumer Reports testing, a Toyota Camry, going at a speed of 65 mph, reduced gas mileage by about 1 mpg. Opening the windows at 65 mph had negligible effects.

Myth or Fact? Additives in gasoline affect mileage.

Fact: In general, gasoline additives can affect engine performance. According to API, deposit control additives, which are found in all gasoline by law, keep engines clean and make them run more efficiently. Deposits in carburetors or in fuel injectors, for example, can affect the engine’s overall air-fuel ratio as well as an individual cylinder air-fuel ratio, which in turn can affect fuel economy, emissions and drivability. Another example is reformulated or "summer-blend" gas, which is composed of oxygenated chemicals. According to the EPA, reformulated gas causes a 1-3% decrease in a vehicle’s fuel economy.

Myth: Buying premium gasoline improves mileage.

Fact: Premium gasoline contains higher octane grades. The octane number measures a fuel’s resistance to engine knocking or pinging – abnormal combustions that could damage the engine. According to Consumer Reports, most engines are designed for an octane rating of about 87 (regular gasoline); engine performance does not increase with a higher octane level than recommended. On the other hand, engines designed to run on premium gas can run on regular gas, without knocking, but with a decrease in fuel efficiency.

Myth: Fuel-saving devices increase fuel efficiency.

Fact: According to Consumer Reports, the fuel-saving devices they tested provided zero or negligible improvements in vehicle fuel economy.

Myth or Fact? Gas purchased in the summer can decrease a vehicle’s fuel economy.

Fact: According to the EPA, in certain high-ozone areas, the EPA mandates the use of special reformulated gasoline (RFG) during the summer months. In California, RFG is required year round. Reformulated gas causes a small decrease (1-3%) in vehicle fuel economy compared to conventional gas.