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What Are Spark Plugs?

Oct 1, 2021 ·

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Spark plugs might be small parts on a vehicle, but they play a big role in helping it function on a daily basis.

Even with the continuing technological changes in automobiles, the mighty little spark plug has always been a big piece of the puzzle. Whether engines are one cylinder or eight, one camshaft or four, carbureted or fuel-injected, the spark plug has been there the whole way.

The spark plug is responsible for delivering a quick, high-voltage jolt of electricity to initiate the explosion we call combustion. Let’s discuss the combustion process to truly recognize and respect the spark plug’s role in the operation.

How Do Spark Plugs Work?

For the internal combustion engine to function and produce power, it needs three things: air, fuel and ignition.

Air is funneled toward a cylinder’s combustion chamber using an intake system. The fuel system uses multiple components to deliver fuel — we’ll use gasoline in this example — either to the intake or directly to the chamber. This is done with the intent that these two ingredients will mix to form a combustible recipe.

To get the explosion, an ignition system delivers high voltage to the spark plug, which protrudes into the cylinder. The tip of the spark plug uses electrodes separated by a small gap. High voltage is necessary to jump the gap, which then produces the ever-so-important spark.  

Each cylinder has ports or valves to let in the air and fuel (and to let out the exhaust), as well as a piston, which moves to create a pumping action to draw in and compress the combustible air/fuel mixture.

When the spark is delivered at just the right moment, what started as chemical energy from the air/fuel mix gets converted to heat energy from the explosion and then to mechanical energy, which moves the crankshaft and eventually the drivetrain.

Each spark typically lasts about 1 millisecond. That’s 0.001, or one one-thousandth of a second! And the whole process will repeat thousands of times per minute.

Fun Fact: Diesel engines do not use spark plugs! They operate using very high compression, which creates very high temperatures, to then auto-ignite diesel fuel. Some diesel engines do use glow plugs to help create more heat when starting, especially in cold weather.

Are There Different Types of Spark Plugs?

Spark plugs vary in many ways, from size or reach, to heat range, and even in electrode design. Spark plugs use ceramic as an insulator, which helps manage heat and prevents the electrical spark from grounding out.

Manufacturers specify which plug to use in every engine application. The most common characteristic of a spark plug has to do with the types of metal used:

  • Copper: These spark plugs feature a center electrode that has a copper core coated with a nickel alloy. These are inexpensive, but not widely used today since they aren’t very durable.
  • Platinum: These are similar to copper plugs, but the center electrode (and sometimes the ground electrode) use platinum. They are more durable and allow for a longer lifespan.
  • Iridium: These are the longest-lasting plugs and are more heat-resistant than platinum. These plugs also use a small center electrode, which requires less voltage to generate a consistent spark.
  • Ruthenium: This is one of the newest precious metals to be used in spark plugs. They claim improved durability over iridium, but carry a higher price tag.
  • Silver: These plugs feature silver-coated electrodes and may be seen in some performance applications. They aren’t very common, since they are costly yet not as durable as platinum or iridium.

How Do You Know When a Spark Plug Has Failed?

Since spark plugs play an important role in the combustion process, one or more symptoms may develop that could indicate failure. Further diagnosis might be necessary, but here are some of the possible concerns:

  • Difficulty starting vehicle
  • Rough idle due to misfiring
  • Loss of power
  • Poor fuel economy
  • Increased emissions

A spark plug issue could also cause the check engine light to turn on or flash. If you experience any of these warning signs, be sure and take your vehicle to a trained automotive technician to have the concern diagnosed. A proper diagnosis is important to ensure the correct repair is performed.

Benefits of Changing Spark Plugs

Service intervals vary, with most manufacturers recommending spark plug replacement between 60,000 and 100,000 miles on late-model vehicles. Specific application and vehicle usage will need to be considered as well.

When spark plugs are replaced, you’ll likely notice some of the following benefits:

  • Improved power, increased fuel economy and reduced emissions: These three issues are a direct result of spark plug efficiency. A plug that fires efficiently will help keep things in check.
  • Smooth running: Whether it be starting, accelerating or cruising, a properly performing spark plug keeps things running just right.
  • Reduced risk of catalytic converter failure: Misfiring of spark plugs can cause unburned fuel to collect and overheat in the exhaust, which has the potential to damage the catalytic converter. If a failure is left unresolved, this can get expensive.

Train to Work on Internal Combustion Engines

In the Automotive Technology program offered at Universal Technical Institute (UTI), you can learn about the different components important to the combustion process, including spark plugs.

The Automotive Engine Service & Repair course specifically covers the fundamentals of internal engine operation and the various components making up the internal combustion engine. This is just one of many courses that could teach you the skills you need to work in an in-demand career as an automotive technician.1 In fact, there are more than 73,000 estimated average annual automotive job openings in the United States.41

You can graduate in less than a year7 from UTI with hands-on experience employers are looking for. Take advantage of the opportunities and request more information here.

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1) UTI is an educational institution and cannot guarantee employment or salary.

2) For program outcome information and other disclosures, visit

7) Some programs may require longer than one year to complete.

41) For Automotive Service Technicians and Mechanics, the U.S. Bureau of Labor Statistics projects an annual average of 73,300 job openings between 2021 and 2031. Job openings include openings due to net employment changes and net replacements. See Table 1.10 Occupational separations and openings, projected 2021-31, U.S. Bureau of Labor Statistics,, viewed October 13, 2022. UTI is an educational institution and cannot guarantee employment or salary.

Universal Technical Institute of Illinois, Inc. is approved by the Division of Private Business and Vocational Schools of the Illinois Board of Higher Education.


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