Automotive supply shops such as AutoZone and O'Reilly Auto Parts carry spark plugs. Over time, as spark plugs develop wear and tear, it's necessary to change them to maintain optimal performance of the engine.
There are six warning signs that it is time for a new spark plug. If the engine sounds rough when the car is idling and the car is vibrating, a mechanic needs to look at the engine. If the car doesn't start easily and the battery isn't the culprit, worn spark plugs can be the cause. Engine misfire, elevated fuel consumption, hampered acceleration and engine surges are also warning signs that a new spark plug is necessary.
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.