Fuel Information
How can I put more than 15 gallons of gas in my tank when it only holds 15 gallons?
The 15-gallon capacity listed in your car’s manual is more of a general guideline rather than a strict limit. In reality, most fuel tanks have a bit of extra room, often between 1/2 to 2 gallons, to accommodate fuel expansion and other factors. Keep in mind that your gas gauge is an estimate, and your tank itself hasn't been precisely calibrated, which can result in being able to fill slightly more than its stated capacity. You can find a more detailed explanation in this NIST Fuel Tank Accuracy document.
How does the gas pump know to shut off?
Providing that the nozzle is functioning correctly, it will make the pump shut off.
The video to the right will help better explain how that work.
Common Types of Fuel Available For Vehicles
Gasoline (Unleaded):
Comes in different octane levels (usually 87, 89, and 91+), with higher octane levels used in high-performance engines
Cleaner-burning than in the past due to government regulations reducing harmful emissions
Diesel:
Used for trucks, buses, and some cars, especially in heavy-duty applications
Clear Diesel: taxed and used for on-road vehicles
Dyed Diesel: non-taxed and dyed red to indicate its for off-road vehicles
Ethanol Blends (E10, E15, E85):
A mix of ethanol (a renewable fuel made from plant materials) and gasoline
E10 (10% ethanol, 90% gasoline) is widely available and works in all vehicles
E85 (85% ethanol, 15% gasoline) is for Flex Fuel Vehicles (FFVs) only and can reduce greenhouse gas emissions
Common Misconceptions About Fuel
"Premium Gas Improves Fuel Economy for All Cars": Not true. If your car is designed to run on regular gasoline, using premium won’t give you more miles per gallon or improve performance.
"Filling up in the morning saves you money": The idea is that fuel is denser when it's cold, so you get more for your money. In reality, fuel storage tanks are insulated, so the temperature barely changes throughout the day.
"Topping off your tank prevents evaporative emissions": False. Modern vehicles are designed to prevent fuel evaporation and topping off can actually harm your car’s vapor recovery system.