Do Spark Plugs Improve Gas Mileage?

by Krista Martin
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old spark plugs image by Rog999 from

A spark plug is an electrical component of a cylinder head in an internal combustion engine. It generates a spark in the ignition foil in the combustion chamber, creating a gap for the spark to jump across. It also collects the heat that builds up in the combustion chamber and transfers it to the cooling system. The fuel inside the engine cylinders are ignited with the help of the spark plugs. This does not necessarily improve gas mileage; however, a damaged spark plug can be detrimental to the engine and may cause excessive fuel consumption as well as issues in starting the vehicle.

Fuel Additives

Spark plugs consist of spark plug wires that link to the ignition or distributor coils. They can carry as much as 30,000 volts of electricity. Fuels often contain additives that cause the spark plugs to become extremely hot, which could foul the ceramic core nose of the spark plug, affecting the ability of the combustion chamber and the engine cylinders to work properly. When this occurs, the engine consumes more oil because oil is leaking past the piston rings or valve guide. Leaking oil will result in lower gas mileage.

Poor Quality Fuel

Using the wrong fuel in your vehicle can damage the spark plugs. Bad fuel can detonate or break the white ceramic insulator on the top of the spark plug. It can also melt the plug terminals, increasing the temperature inside the engine and potentially causing pistons to melt. The air-fuel mixture becomes ignited prior to the ignition from the spark and the two flames cross paths, producing a clattering noise in the engine. When this occurs, a mechanic will have to decarbonize the engine and advise on proper fuel quality for your vehicle.

Fouled Spark Plug

When a spark plug fouls, it can indicate a rupture in the transmission vacuum modulator diaphragm or that the PCV is clogged. This can also foul the spark plug, affecting not only the gas mileage but emissions as well. In this case, a mechanic will have to replace the faulty device and replace the fouled spark plugs with new ones.

Carbon Buildup

The wrong spark plugs in your vehicle could result in carbon buildup on the plug, which is a dry and black sooty deposit. The engine will fail to burn fuel or it will use too much, reducing the gas mileage. When this occurs, the spark plug should be replaced with the correct heat range. Other causes could include driving habits such as excessive stop and go, a rich fuel mixture or the vehicle has a clogged air filter.

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