If you buy a new or late-model used car, chances are you’ll change vehicles before you need to change the spark plugs. How long spark plugs last varies by manufacturer and vehicle, but on many vehicles today, they should be good for 100,000 or more miles. Some vehicles, though, will have shorter intervals, particularly performance and luxury models.
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That longevity is a product of the electronic controls that precisely manage the air-fuel mixture and when the spark plugs ignite that mixture, as well as improvements to the plugs themselves. The spark plugs in many vehicles today have iridium or platinum tips on the electrodes (the parts that transmit the spark) that last longer than conventional plugs with copper and nickel-alloy electrodes.
How Often Do You Need to Change Spark Plugs?
Because manufacturers use different kinds of spark plugs, the best guide as to when they should be replaced is the maintenance schedule that comes with every vehicle either as part of the owner’s manual or as a separate guide (they can also often be found online).
For example, Toyota recommends changing the plugs every 120,000 miles on a Corolla, RAV4 or 4Runner, but every 60,000 miles on an 86 coupe, which was developed with Subaru and uses a Subaru engine. Ford advises to change the plugs at 100,000 miles on an F-150, Explorer and other models under “normal” driving conditions. If a vehicle frequently tows a trailer or spends a lot of time in stop-and-go traffic or idling, then Ford suggests installing fresh plugs every 60,000 miles. The plugs on BMWs such as the X3 and 3 Series should be changed every 60,000 miles. On some Mercedes-Benz models, it’s as frequent as every 36,000 miles, but on others, the intervals are longer.
Spark plug replacement used to be an integral part of periodic engine “tuneups” that 50 years ago were necessary as often as every 5,000 miles. Now, though, there is no such thing as a tuneup. The only reason to replace plugs more often than recommended is if the engine is hard to start, idles roughly, hesitates, misfires, uses more fuel than usual or if the check engine light comes on. Even under those circumstances, the cause could lie elsewhere, so it’s better to have a technician diagnose the problem instead of reflexively replacing the plugs.
After 75,000 miles or more, spark plug electrodes might be worn or there might be light deposits on them, but the electronic engine controls will adjust the air-fuel mix and spark timing to compensate, so there probably will be only a slight loss of performance or fuel economy, if any. Unless the engine is performing poorly, replacing the plugs ahead of schedule might not produce dramatic improvements and the cost could outweigh the benefit.
When manufacturers say that maintenance such as replacing spark plugs should be done only every 100,000 miles or longer, many vehicle owners think of them as lifetime parts. However, there are limits even for iridium-tipped plugs, and some manufacturers, such as Toyota, warn that not replacing them on schedule can void the emissions warranty.