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It wasn’t that long ago that people used to try and save gas by leaving their cars running when going into a convenience store instead of restarting them when they came out. The theory back then was that starting your car used more gas than leaving it idling for short periods. Some people still do this today, but does it save gas in newer cars?

Does it take a lot of fuel to start a car?

A removed hood on an Aston Martin car with engine, powertrain, and fuel injectors
A removed hood on an Aston Martin car | Len Trievnor/Express/Hulton Archive/Getty Images

Cars built before the 1980s provided the air-fuel mixture the engine burns using a different system than used by vehicles made in the last 30 years. This early system used carburetors to spray fuel into the airstream feeding the engine, and while there was some room for adjustment, it had to supply enough gas for the engine under any condition. This requirement meant that the air-fuel mixture was “rich” with fuel most of the time.

There isn’t a continuous airstream feeding the engine with the carburated engine shut off. So, carbureters have to dump excess fuel into the engine’s air intake during start-up to ensure easy starting. 

Newer cars employ a computer-controlled fuel injection system that delivers precise amounts of fuel to each car engine cylinder only when needed. It Still Runs tells us that, on average, it only “takes about 1/2 teaspoon of gas to start the engine.” While this varies slightly depending on the engine’s size, the number of cylinders, and tuning, it’s a predictable average to keep in mind. 

The South Carolina Department of Health and Environmental Control also published a fact sheet stating that an idling car engine “uses up to 1/2 gallon of fuel per hour.” For reference, there are 768 1/2 teaspoons in a 1/2 gallon.

Will one gallon of gas start a car?

Now that we know that most car engines will start on 1/2 teaspoon of gas, that seems like a simple answer. So, how much gas needs to be in your gas tank to start your car? If your car’s gas tank is empty, adding 1 gallon of gas should be enough for the fuel pump to pick it up and deliver a fuel stream from the tank to the engine. 

Will a car start if it’s out of gas?

If a car runs out of gas, the car’s engine will shut off. If you try to start it again without adding gas, it may try to start, sputter, run for a second or two, and then die again. A gasoline-powered car will not run without a sufficient amount of gas. 

If you keep trying to get it to start without enough gas in the gas tank, it could damage your car’s fuel system components or engine. For example, your vehicle employs a fuel pump to send gas to the engine’s injectors from the gas tank. This fuel pump relies on the gasoline it pumps to provide lubrication and cooling and could overheat without it. Additionally, your engine will suffer as burning an air-fuel mixture that is lower on fuel than designed causes explosions within the cylinders that can break spark plug tips and burn engine valves.


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