Spark plugs are available at Auto Zone, Wal-Mart and Amazon.com. Spark plugs supply the spark to fire the fuel in many internal combustion engines. Usually, the number of spark plugs the vehicle owner needs is equal to the number of cylinders in the engine.
Dirty or fouled spark plugs reduce the fuel economy of an engine. Replacing older plugs with new ones is one way to improve the overall efficiency of the vehicle. While some manufacturers claim installing plugs with rare metal electrodes improves economy, HowStuffWorks indicates that any new plug with the proper heat rating improves mileage.
The heat rating of a plug indicates its ability to dissipate heat. Cold plugs have less insulation and remove more heat from the engine to the cooling system. Hot plugs have more insulation, keeping the engine running hot. The additional heat helps to burn off any carbon deposits on the plug, increasing the time between changes.
Manufacturers design spark plugs to continue working correctly for 30,000 to 100,000 miles. The owner's manual for the car should indicate when the number of miles between changes. When changing the plugs, it is essential that the installer not cross the wires. Crossed wires lead to misfiring of the engine.