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Summary
  • Ordinary spark plugs should last anywhere between 30,000 and 50,000 miles.Meanwhile, iridium spark plugs can last up to 100,000 miles without encountering any issues.
  • Overheating, contamination, and carbon fouling can decrease a spark plug’s lifespan.
  • Regularly inspect the electrodes and maintain the ideal gap to make your spark plugs last longer.

The spark plug is responsible for igniting the air-fuel mixture inside the combustion chamber. Since spark plugs are regularly exposed to a lot of heat, they will eventually wear out and need to be replaced. However, their lifespan isn’t set in stone and can vary due to several factors.

What’s the Replacement Interval of Spark Plugs?

In the 1960s and ‘70s, spark plug intervals were about 12,000 miles between “tune ups,” which included points and condenser in the distributor, along with timing and carburetor adjustments.

But by about 1980, spark plug replacement intervals had increased dramatically, presumably because electronic ignition created a spark that was so much hotter than the old points-and-condenser systems.

After about 1980, which typically called for spark plug replacement at about 30,000 miles, it wasn’t unusual to find that a car owner had driven over 100,000 miles without replacing the spark plugs and yet had no issues. As model years came and went, spark plug replacement intervals increased to 100,000 miles.

See also  How to Change Spark Plugs

A spark plug’s lifespan depends on its type. Spark plugs vary according to the different metals used in their electrode tips.

Ordinary spark plugs made from copper and nickel should last 30,000 to 50,000 miles but may last as much as twice that many miles. Spark plugs made from platinum and iridium last longer. Platinum spark plugs typically last for 60,000 miles, while iridium spark plugs can last anywhere between 80,000 and 100,000 miles. But as mentioned, spark plugs may last as much as twice that many miles.

spark plug replacement on a 2008 ford explorer
The spark plug pictured in the photo was replaced as part of a set during a routine checkup on this 2008 Ford Explorer at 238,000 miles. The vehicle had no driveability symptoms at all. The paint spot on top of the spark plug and the part number of the plug itself indicated that the spark plug had been in that 4.0L since the vehicle was new. | Image Source: Richard McCuistian.

Factors that Affect Your Spark Plug’s Lifespan

A spark plug’s lifespan depends heavily on how the spark plug’s electrode wears out. The electrode is where the spark is generated, from which it jumps to a protruding hook. Other factors can accelerate the rate at which your vehicle’s spark plug wears. As a result, the manufacturer’s replacement interval might not match the rate at which your spark plug is wearing out.

types of ignition systems affect spark plug wear
Different types of ignition systems will also affect spark plug wear and spark plug change intervals. The two spark plugs in the photo were fired by the same coil over many tens of thousands of miles on a coil pack system where the coils are fired in pairs. One of the spark plugs will wear the center electrode more and the companion plug will wear the ground (side) electrode more because of the way the spark travels on each plug. | Image Source: Richard McCuistian.

Overheating Damage

Frequently driving your engine at its limit, such as driving your car on the track, can overheat spark plugs and cause the electrode to wear faster. A spark plug can also be exposed to excess heat if an engine has incorrect ignition timing or an incorrect fuel-to-air ratio.

spark plug tip destroyed by the heat
The spark plug in the photo had only been in the engine for about 100 miles. It had only been screwed halfway in, and the washer that carries heat out of the spark plug and into the cylinder head never made contact with the seat. All the heat went into the threads and the spark plug’s tip was destroyed by the heat. The washer or the beveled seat on spark plugs is designed to carry heat out of the plug and into the cylinder head. Plugs won’t always fail this way when left loose, but this one did. It doesn’t happen a lot, but an intake valve leak can also cause spark plugs to be destroyed by heat very rapidly like this. | Image Source: Richard McCuistian.

Oil Contamination

oil clogged sparks plug tip
Sometimes, oil can clog the spark plug’s tip. Piston oil rings can cause this even if the compression rings are still good. But if you remove a plug that is oil and fuel-soaked (see photo), it’s possible that the spark plug has just stopped firing and needs replacing unless the engine is smoking and/or using a lot of oil. | Image Source: Richard McCuistian.
valve stem seals will leak when the engine is shut off
Valve stem seals will cause a different kind of deposit than oil from piston ring issues. Valve stem seals will leak when the engine is shut off and will cause large amounts of blue smoke when first started, then may either only cause smoke at idle or maybe not at all while the engine is running. Valve stem seals will cause hard, puffy deposits such as the ones in the photo and may cause random misfires or mild surging.  | Image Source: Richard McCuistian.

Carbon Buildup

soot or carbon can deposit itself on the edge of the spark plug
Soot or carbon can deposit itself on the edge of the spark plug, preventing the plug from generating a spark. The plug may spark, but soot like this isn’t a spark plug problem, it points to other issues that need to be addressed. An engine can generate more soot and carbon when the engine is using a rich fuel mixture, which can be caused by a wide range of engine problems. | Image Source: Richard McCuistian.

Octane Booster Fouling

spark plugs developed red conductive dust
Some Octane boosters will coat the spark plugs with a red, conductive dust that can cause misfires and surges. These spark plugs developed this red, conductive dust and surging misfires on car with only 11,000 miles due to the use of a certain kind of octane booster. | Image Source: Richard McCuistian.

What You Can Do to Make Spark Plugs Last Longer

Just like many vehicle components, proper maintenance and care can make spark plugs last longer. If you know your way around your vehicle’s engine, here are a few things you can do to maximize your spark plug’s lifespan:

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Regularly Inspect the Electrodes

The spark plug’s electrodes typically fail when they become clogged with soot, oil, or rust. Pulling them out for inspection and cleaning them can help them last longer.

Pick Good Spark Plugs

When it’s time to replace your spark plugs, pick the ones that are recommended by the manufacturer, which can be found in the owner’s manual. You can also ask your mechanic if it’s recommended to fit your vehicle with spark plugs that have longer lifespans.

Maintain the Gap

If a spark plug gap is too close, it can cause a random idle misfire that may not even be noticeable at higher rpm. If the gap is too wide, it can cause misfires under high rpm load.

You should maintain the gap as prescribed by your owner’s manual. There are also tools that are made specifically for checking and maintaining the spark plug’s gap. Setting the gap a few thousands wider than a narrow factory spec will typically help with idle quality and starting. For example, if the spark plug gap calls for .042 to .046, you can set the plug gap at .050 and the engine will idle better and start better. But if the called-for gap is .050 or more, just use the factory spec.

Always check the spark plug gap on replacement plugs even if they’re supposed to be pre-gapped because you don’t know how they were handled while they were still in the box. Keep in mind that all the plugs need to be gapped the same.

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Some tools for setting spark plug gaps may require more advanced automotive DIY skills. That said, if you follow these maintenance tips, then your spark plugs have a good chance of reaching their intended lifespan.

Where to Get New Spark Plugs for Your Vehicle

It’s a good idea to replace your vehicle’s spark plugs once they fail. After all, they can cause engine misfires, poor fuel economy, and other problems that can make driving a hassle. Luckily, you can find replacements for both ordinary and iridium spark plugs easily at CarParts.com.

You won’t even have to take one step outside your door to get yourself some new spark plugs. Simply use your mobile device or computer to visit our website. Then, input your ride’s specs into our vehicle selector and use the search filters to find the perfect spark plug replacements in no time.

We make it a point to get our spark plugs from the most trusted manufacturers in the industry. Plus, our warehouses are strategically located all over the US, meaning you can receive your order within days.

Get yourself some spark plugs that are built to last. Shop now and take advantage of our unbeatable deals!

About The Authors
Written By Automotive and Tech Writers

The CarParts.com Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by CarParts.com's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Reviewed By Technical Reviewer at CarParts.com

Richard McCuistian has worked for nearly 50 years in the automotive field as a professional technician, an instructor, and a freelance automotive writer for Motor Age, ACtion magazine, Power Stroke Registry, and others. Richard is ASE certified for more than 30 years in 10 categories, including L1 Advanced Engine Performance and Light Vehicle Diesel.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

File Under : Ignition System , DIY Tagged With :
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