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How Long Do Spark Plugs Last?

202501 how long do spark plugs last scaled jpg How long do spark plugs last | Cars.com illustration by Paul Dolan

How long spark plugs last varies with different cars and different types of spark plugs. Older cars often had to have their spark plugs replaced every 5,000 to 10,000 miles, while some newer cars — with computer controls and more modern plugs — can go more than 100,000 miles on a set of plugs. As is often the case, the best source of service information for your vehicle is the owner’s manual. If you don’t have it, you can often find an electronic version online by searching, “Owner’s manual for (year/make/model).” 

Related: Do Diesel Engines Have Spark Plugs?

What Is a Spark Plug?

The typical automotive spark plug is about the size of your index finger. There is usually one for each engine cylinder, though a few cars have two plugs per cylinder. A spark plug creates a spark in the engine’s combustion chamber (inside the cylinder between the piston and the cylinder head), which ignites the air-fuel mixture to generate power.

The top of the spark plug — the end outside the engine you can sometimes see — connects to either a spark-plug wire or an ignition coil (sometimes called “coil-on-plug”). The bottom of the spark plug is inside the engine’s combustion chamber and has a small center electrode and a side electrode, the latter often a little L-shaped piece that extends from the side of the plug over the center electrode. The spark that ignites the fuel mixture jumps through a gap between these two electrodes. 

Both electrodes can wear away over time, extending the gap between them through which the spark jumps — which is ideally very tightly controlled. The plugs can also accumulate carbon deposits (a byproduct of burning the air-fuel mixture), which can cause them to fail to produce a spark, or “foul.” Different spark plugs use different types of tips, some of which wear longer or resist fouling better.

Types of Spark Plugs

Prior to the 1980s, the most common spark plugs were copper spark plugs, which used a copper center electrode, often covered with a harder nickel alloy to reduce wear. Starting in the 1980s, platinum-tipped spark plugs that lasted far longer than copper plugs came along (platinum is a much harder material). They also ran hotter, which reduced fouling. Some of these plugs use platinum only on the center electrode (sometimes called “single platinum”), while others add a platinum side electrode (“double platinum”).

Starting in the mid-1990s, iridium-tipped plugs appeared. Iridium is even harder than platinum, so these plugs were intended to last longer. They are also claimed to slightly increase combustion efficiency. The newest of the breed are ruthenium spark plugs, which are supposed to last a little longer than iridium and provide even better combustion properties.

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What Type of Spark Plugs Should I Use?

The safest bet is to use the same type of spark plugs that originally came on your car. Keep in mind, though, that if you have an older car you bought used, the original plugs may have been replaced with a different type than originally came on the car, so checking what it had originally is a good idea.

However, if it’s an older car that originally came with copper spark plugs, moving up to platinum plugs should give you a much longer service life. Note that some newer cars — often with turbocharged or high-compression engines — come standard with copper spark plugs, and those should be replaced with the same.

Iridium spark plugs are found on many newer cars and may be considered an upgrade from platinum plugs, and ruthenium plugs are a further step up. Although there’s a corresponding price jump for each, the added cost could easily be justified, particularly if the plugs are really difficult to change and you plan on keeping the car for a very long time.

Prices for each type of spark plug can vary greatly. In general, copper plugs are less than $4 each, platinum plugs range from about $6 (single platinum) to $20 (double platinum) each, iridiums from $8 to $30 each, and ruthenium ones from $12 and up.

Considering their importance, most spark plugs are relatively cheap, so it’s worth changing them when called for. And with many modern cars, it’s likely you’ll only have to change the spark plugs once or twice in the vehicle’s lifetime, a vast improvement over the annual tuneup that used to be required back in the “good old days.”

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