Without operational spark plugs, your engine won’t run. If even just one plug were to fail, the change in functionality would be very noticeable. Your engine would run rough, it would idle poorly, it might spit and sputter during acceleration, and it might even stall out on you. Spark plugs do wear out over time, although the actual lifespan varies depending on the type of plug in question, the condition of your engine, and your driving habits.
Wear factors for spark plugs
There are several factors that play a role in spark plug health, but the most common reason for them to wear out is that they’re just old. To understand this, you need to know a bit more about how spark plugs work.
When your alternator generates electricity, it is sent through the ignition system, down the spark plug wires, and to each individual spark plug. The plugs then create electrical arcs at the electrodes (the small metal cylinders protruding from the bottoms of the plugs). Each time a plug fires, a minute amount of metal is removed from the electrode. This shortens the electrode, and requires more and more electricity to create the arc necessary to fire the cylinder. Eventually, the electrode will be so worn that it won’t arc at all.
This is what happens in a normal, properly maintained engine. There are other factors that can reduce plug life (all spark plugs eventually wear out; it’s just a question of when).
Overheating Damage: Overheating spark plugs can cause the electrode to wear faster. Pre-ignition from an improperly timed engine can cause this, as can an incorrect air to fuel ratio.
Oil Contamination: If oil seeps onto the spark plug, it will foul the tip. This creates damage and additional wear (oil seeping into the combustion chamber is something that happens over time as seals begin to fail).
Carbon: Carbon buildup on the tip can also cause premature failure. This can happen due to dirty injectors, a clogged air filter and many other reasons.
As you can see, there are a number of different factors that affect when your spark plugs will fail, and just how much use you’ll get out of them.
This article originally appeared on YourMechanic.com as What Causes Spark Plugs to Wear Out? and was authored by Valerie Johnston.