If your car starts well and runs smoothly, it means that you’ve maintained it well. It also means that the spark plugs in your engine are working. They ignite the air-fuel mixture in the cylinders; each cylinder has one spark plug.
Why do spark plugs need to be replaced? Over time they wear out, become contaminated and eventually fail.
When should spark plugs be replaced? There are two types of spark plugs: conventional and long-life. Conventional spark plugs need to be replaced every 30,000-50,000 miles. Long-life (iridium- or platinum-tipped) spark plugs need to be changed between 60,000 and 150,000 miles, depending on the vehicle. The recommended replacement intervals are posted in the Maintenance Schedule, which can be found in the owner’s manual or in a separate Warranty and Maintenance brochure for your car. Spark plugs may also need to be changed earlier if there is a problem with them.
What are the signs that spark plugs are worn out? In some cars, you might notice that the engine doesn’t start as easily as before. It may run a little rough or hesitate when accelerating, especially when it’s cold. Old, worn-out or contaminated spark plugs can cause poor gas mileage. Often, though, there are no symptoms until one of the old spark plugs stops working, causing the engine to misfire. The term “misfire” means that the affected cylinder is not firing up. For example, if one cylinder misfires in a 4-cylinder engine, it will run on only three cylinders. An engine that misfires runs rough, shakes and lacks power. The “Check Engine” warning light flashes on and off or stays on solid.
Should spark plugs be changed earlier as a precaution? It depends on the mileage. For example, if your car has long-life spark plugs that are due at 100,000 miles and your dealer recommends changing them at 50,000 miles, it’s too early.
Can long-life spark plugs last past the recommended intervals? Yes, we have seen iridium spark plugs last longer, but at higher mileage old spark plugs are more likely to cause ignition coil failures. Long-life spark plugs have more durable electrodes, but they often fail because carbon deposits accumulate on the electrodes, as in the top photo.
Do spark plug wires need to be replaced together with spark plugs? Yes, it’s usually recommended. Old spark plug wires become brittle and tend to crack. Of course, many modern cars don’t have spark plug wires.
Can spark plugs be cleaned? In old cars, it was a common maintenance job to clean spark plugs and adjust gaps between the electrodes. In modern cars, long-life spark plugs are not serviceable and are simply replaced