What Are Spark Plugs?

Spark plugs are small but important parts in a vehicle that play a big role in how it functions. They are responsible for delivering a high-voltage jolt of electricity to initiate combustion in the engine.

Even with the continuing technological changes in automobiles, the mighty little spark plug has remained 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.

What do spark plugs do? Spark plugs create a spark between two electrodes, which ignites the air/fuel mixture in the combustion chamber. There are different types of spark plugs, including copper, platinum, iridium, ruthenium and silver, each with their own characteristics and durability.

Signs of a failing spark plug include difficulty starting the vehicle, rough idle, loss of power, poor fuel economy, increased emissions and an illuminated check engine indicator.

Let’s discuss the combustion process to 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 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, 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 necessitate expensive service.

Spark Plugs FAQs

What are the different types of spark plugs?

There are five types of spark plugs: copper, platinum, iridium, ruthenium and silver.

How often should spark plugs be replaced?

Every car has a different standard for when its spark plugs need to be replaced. Typically, spark plugs should be replaced every 18,000 – 100,000 miles. Consult your car’s owner’s manual to see the recommended time frame to replace them.

What are the signs of a bad spark plug?

Signs of a bad spark plug or spark plugs needing to be replaced include:

• Check engine light is on
• Misfiring engine
• Issues with accelerating
• An abnormally loud engine

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 Introduction to Engines course specifically covers the fundamentals of 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 pursue an in-demand career as an automotive technician.¹ In fact, there are more than 67,000 estimated average annual automotive job openings in the United States.⁴¹

You can graduate in less than a year from UTI with hands-on training in skills employers are looking for.^7,18 Take advantage of the opportunities and request more information.

UTI Campuses That Offer Automotive Technician Training

• Avondale, Arizona
• Long Beach, California
• Rancho Cucamonga, California
• Sacramento, California
• Miramar, Florida
• Orlando, Florida
• Lisle, Illinois
• Bloomfield, New Jersey
• Mooresville, North Carolina
• Exton, Pennsylvania
• Austin, Texas
• Dallas/Fort Worth, Texas
• Houston, Texas