Ethylene dibromide prevents the tetra-ethyl lead from forming lead oxide deposits on spark plugs and on valve seats and stems. Red dye is added to identify an ethyl treated gasoline and to warn against its being used as anything but an engine fuel. In 1975, it became illegal to use a leaded gasoline except in cars built prior to this time. With the addition of the catalytic converter, it is undesirable to burn leaded fuel, because leaded fuel will clog the converter and increase the back-pressure of the exhaust. All modern fuel systems are fed through a pump, so the fuel tank is usually at the rear of the chassis under the trunk compartment.
Some vehicles have a rear engine with the tank in the forward compartment.
The fuel tank stores the excess fuel until it is needed for operation of the vehicle. The fuel tank has an inlet pipe and an outlet pipe. The outlet pipe has a fitting for fuel line connection and may be located in the top or in the side of the tank. The lower end is about one-half inch above the bottom of the tank so that collected sediment will not be flushed out into the carburetor. The bottom of the tank contains a drain plug so that tank may be drained and cleaned.