The Importance of New Spark Plugs Every 60,000 Miles

Replacing spark plugs & ignition coils are the closest thing to a “tune-up”that can be done on modern cars.

On a few of the cars from 2002 ( 7 series ) and ending with the 2006 3 series there are reminder service icons calling for the replacement of the spark plugs at different set mileages. None of the BMW’s since then display this service request any longer & owners must rely on their own record keeping or the recommendation of a particularly conscientious service adviser. Nevertheless, the average BMW / MINI should have the spark plugs replaced at 60,000 miles while some sport engines require them at even earlier mileage.

Here’s a picture comparing a new spark plug to an old one. Believe me some of the old ones we take out of engines look worse than the old one depicted.

Why do spark plugs need to be replaced? Over time they wear out, become contaminated and eventually fail.

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 a4-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.

Often a worn-out spark plug can cause an ignition coil to fail. The ignition coil is the part that generates high-voltage impulses to create an electric spark. The ignition coil failure is the #1 reason most engines start running rough but not the only reason.

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.

If your engine is good on gas and runs like new, consider waiting until closer to the recommended mileage.

Do all spark plugs need to be replaced at the same time? Yes, spark plugs are usually replaced as a set. It's important to use the correct parts, as wrong spark plugs may cause problems. It's also vital to carefully inspect new spark plugs before installation. If a new spark plug has been dropped on a hard floor, the insulator might be cracked. Cracks in the insulator are visible on close inspection.

Do all spark plugs need to be replaced if an ignition coil fails? If one of the ignition coils fails and spark plugs haven't been changed in awhile, it's a good idea to change all of the ignition coils and all of the spark plugs as a precaution. If spark plugs are fairly new, replacing one spark plug and the ignition coil in the affected cylinder might be enough.