Spark Plugs In Automobiles: a detailed Description

Spark Plugs are indispensable devices in the ignition system of automobiles. A faulty sparkplug can affect the functionality or effectiveness of your automobile. One, therefore, has to ensure that their spark plugs are good and very functional. This article would tell you all you need to know about spark plugs in an automobile through a breakdown of the subheadings below.

What is a Spark Plug?

A spark plug is an electrical device that is used in the internal combustion chamber of mechanical engines to ignite compressed gasoline (Petrol) using an electric spark.

It fits into the cylinder head of an internal combustion engine and carries two electrodes separated by an air gap, across which current from a high-tension ignition system discharges, to form a spark for igniting the air–fuel mixture. Spark plugs are used heavily in automobiles such as trucks, buses, tractors, boats, aircraft, motorbikes, scooters, industrial engines, power mowers, and chain saws.

spark plugs

In plain terms, spark plugs turn an energy source (gasoline) into locomotive motion. For instance, we have petrol which is highly flammable and also air, that could cause an explosion when mixed. The plug is like lighting fire to the compressed gas.

Types of Spark Plugs

Each automobile requires a particular type of spark plug made from specific materials and with a designated spark plug gap set by the engineer during installation. However, they all perform the same function of transmitting an electrical signal sent from the ignition coil at a preset time to create a spark that ignites the air/fuel mixture inside the combustion chamber. There are five major types of spark plugs in automobiles.

  • Copper/Nickel Spark plugs
  • Iridium Spark plugs
  • Single Platinum Spark plugs
  • Double Platinum Spark plugs
  • Silver Platinum Spark plugs

Copper/Nickel Spark plugs

Copper with Nickel Spark plugs

In this type of spark plug, the center electrode is made of Copper coated with a Nickel alloy. It is characterized by the largest diameter of all other Spark plugs. Hence, more voltage is required to generate a spark. Nickel alloy material is soft and flimsy so they need to be replaced more often.

However, Cars have specifications of the kind of Spark plugs required in automobiles differ. Be sure to check because installing another type of Spark plug may be considered not necessary.

Benefits of using Copper Spark plugs.

  • These types of Spark plugs are relatively less expensive.
  • They are the appropriate Spark plugs for vehicles built on/ before the 20th century(especially before the year 1980).
  • It performs well under high compression.


  • It has a shorter life span.
  • Most Copper Spark plugs need to be changed every 20 miles or so.
  • It requires high voltage to produce a spark.

Iridium Spark plugs

Iridium Spark plug

Iridium as a material is stronger and harder than Platinum. Hence, they have higher longevity compared to Platinum. It lasts up to 25 percent longer than Platinum. The high melting point of iridium makes it easier to produce great electrodes while retaining its characteristics.

These Spark plugs have small center electrodes. It, therefore, requires less voltage to generate a spark compared to Copper Spark plugs. These Spark plugs are being used now in most automobiles.

Benefits of using the Iridium Spark plugs.

  • Iridium spark plugs support more complete combustion.
  • It is more durable with a long life span.
  • It requires less voltage to generate a spark.

Disadvantages of using an Iridium Spark plug.

  • It is quite expensive.

Single Platinum Spark plugs

A single platinum Spark plug has a platinum disc welded on the center electrode instead of a nickel alloy only. It generates more heat which burns deposit off the Spark plug hence prevents fouling.

Benefits of using the Single Platinum Spark Plug

  • The single Platinum spark plug has a long life span.
  • It could last for about 100,000 miles
  • It also has the advantage of reducing carbon build-up.

Disadvantages of using a Single Platinum Spark Plug

  • It is relatively expensive.

Double Platinum Spark Plugs

The double Platinum Spark plugs in automobiles have a Platinum coating on both the center and sides electrodes. It is used mostly when the ignition system is a wasted spark system. It causes the spark plugs to fire twice.

While one spark occurs in the compression stroke's cylinder,  the other occurs in the exhaust stroke's cylinder. Double Platinum Spark plugs in automobiles are more efficient and have higher longevity. It exerts more wear on both electrodes than other ignition systems.

Benefits of using a double Platinum Spark Plug

  • It is recommended for a wasted spark ignition system
  • it is very reliable

Disadvantages of using a Double Platinum Spark Plug

  • It is quite expensive
Iridium Vs Platinum Spark Plugs in automobiles

Silver Spark Plugs

The Silver Spark Plugs are quite rare compared to the others. It has Silver coated electrode tips. It does not have high longevity compared to Iridium and Platinum Spark plugs. This is due to the less durability of the Silver. It is, however, used in most European performance cars and Motorcycles.

The benefit of using the Silver Spark Plug.

  • It has very good thermal conductivity.

The disadvantage of using the Silver Spark plug.

  • It has low longevity.
Recommended read:

The Purpose and Structure of a Spark Plug

In mechanical machines mainly automobiles, a spark plug is introduced to provide an electric spark that is hot enough to ignite the air/fuel mixture inside the combustion chamber of an internal combustion engine. This is done by a high voltage current arcing across a gap on the spark plug. Some necessary parts come together to enable the effective functionality of spark plugs in automobiles.

Parts of a spark plug

Parts of a Spark Plug
  • Plug Terminal: This part of the spark plug is connected to the high-tension cable coming from the distributor cap. It conducts the high voltage to the central electrode.
  • Ceramic Insulator: This is made up of Aluminum oxide ceramic and acts as an insulating material for the spark plug. It separates the central electrode from the earth at up to 40000 Volts. It can be rendered in plain form or with profiles to prevent flashover.
  • Metal Body: It is a steel shell manufactured with precision rolled threads for a secure fit, and easy installation and removal. It provides electrical ground to the cylinder head and helps to cool the plug by transferring heat to the cylinder head.
  • Central Electrode: It is made of nickel-based alloys consists of a copper core enclosed in them. Depending upon the type, the central electrode can be in platinum or iridium. The high voltage is applied to the central electrode from the secondary winding through the distributor.
  • Ground Electrode: It is welded to the metal body of the spark plug. It makes a spark path with the central electrode. It is made up of nickel-based alloys (or iridium or titanium reinforcement)
  • Sealing washer/ Gasket: It makes sealing with the cylinder head and helps in heat dissipation.
  • Insulator tip: It is extended into the combustion chamber. It has a greater influence on the thermal rating of the spark plug.
  • Electrode Gap: It is the distance between the central electrode and the ground electrode. The electrode has a crucial role in spark generation. If an appropriate gap is not provided to the plug then it cannot produce sufficient spark to ignite the fuel and may lead to misfiring.

Functions of a spark plug

For years spark plugs have been a critical component of the internal combustion engine of most mechanical machines. The spark plug has two primary functions:

To ignite the air/fuel mixture

When electrical energy is passed through the spark plug, it jumping the gap within the spark plugs firing sparks if the voltage equipped to the plug is high enough. This electrical spark ignites the gasoline/air mixture within the combustion chamber.

To remove heat from the combustion chamber

Spark plugs cannot produce heat, so inversely they will take heat away. The temperature of the plug’s firing end (insulator tip) should be low enough to forestall pre-ignition, however high enough to forestall fouling.

The spark plug works as a thermal device by pulling unwanted thermal energy from the combustion chamber and transferring heat to the engine's cooling system, and also dissipates heat from the tip.

How do you know a spark plug is failing or bad?

Symptoms of a bad spark plug

Without a spark, there would be no way for fuel to ignite in the combustion chamber. Good spark plugs will burn fuel efficiently, while bad or failing spark plugs can prevent an automobile from starting entirely. Here are some signs to note that indicates a bad or failing spark plug

Slow acceleration

The most common cause of poor acceleration in most vehicles is a problem in the ignition system. Modern engines have multiple sensors that tell the onboard computer and ignition system when to send electric pulses to fire the spark plug, so the issue maybe with a faulty sensor.

However, sometimes the issue is as simple as a worn-out spark plug. A spark plug is composed of materials that work together to produce a spark hot enough to ignite the air-fuel mixture. When those materials wear out, the effectiveness of the spark plug is reduced, which can significantly reduce the acceleration of the vehicle.

If you notice that your car is not accelerating fine or ascends slightly steep hills sluggishly unlike before, it may be attributed to a faulty spark plug that needs to be replaced.

However, you should contact a mechanic to inspect this issue as it could be caused by multiple other factors including a dirty or clogged fuel injector, bad fuel filters, or issues with oxygen sensors.

Poor Fuel Economy

A spark plug that is in good working condition burns fuel efficiently in the combustion cycle. When this occurs, your car can achieve a better-than-average fuel economy. When the plug is not working optimally, it is frequently because the gap between the spark plug electrodes is either too close or too far apart.

In fact, most mechanics will take out spark plugs, examine them, and adjust the gap to factory settings as opposed to replacing the spark plug entirely. If your vehicle experiences an increase in fuel consumption, it very well could be attributed to a worn-out spark plug.

empty fuel tank warning

Engine is Misfiring

Most times if the engine misfires, it's typically due to an issue in the ignition system. In modern cars, a sensor malfunction could be the most likely culprit.

However, it may also be caused by a spark plug wire or the tip of the spark plug that connects to the wire being damaged. An engine misfire can be noticed by intermittent stumbling, sputtering, or drag sounds from the engine. If the engine is allowed to keep misfiring, exhaust emissions will increase, engine power will decrease, and fuel consumption will increase.

Watch this to see practical signs of a misfiring engine

Engine Surging or Hesitating

Another scenario could be the engine hesitating while accelerating. In this case, the engine is not responding correctly to the driver. It could suddenly experience a surge in power, then slow down. The engine is sucking in more air than it should be in its combustion process, causing a delay in power delivery. The combined hesitation and surging could hint a spark plug problem.

Rough Idle

A bad spark plug may cause your engine to sound rough or jerk in some cases while idling. The vehicle-encompassing, jittery sound will also cause your vehicle to vibrate. It can indicate a spark plug problem in which a cylinder misfires only while idle.

Hard to Start

If you have trouble starting your vehicle, it could be a sign your spark plugs are failing. As noted earlier, the engine's ignition system is comprised of multiple individual components that must work cohesively, in order to function properly. At the first sign of problems starting your vehicle, it's a good idea to contact a certified mechanic to take a look at the cause.

Regardless of what the issue might be, you might end up needing new spark plugs when yours eventually wear out. Being proactive about spark plug maintenance can extend the life of your engine by hundreds of thousands of miles.

Starting a healthy engine

watch this to see practical ways of identifying a faulty spark plug

How to Test Spark Plugs

Step 1:  Begin by disconnecting each spark plug wire on your engine one at a time while the engine is ON and idling. If the engine drops speed or starts running rough when one is disconnected, you know that spark plug is good. If you disconnect a spark plug and no significant change happens in the engine, you have discovered a faulty spark plug.

Step 2:  Test the spark plug ignition by disconnecting the spark plug wire from the spark plug. When this is done, hold the end of the spark plug wire close to a metal surface. If the spark plug is good, you will see a spark or you'll hear a crackling noise. This, therefore, means that voltage is getting through the wire to the spark plug.

Step 3:  Check to see if there is a spark on each one of your spark plug wires when the engine is cranked. If compression is good, you will have a spark on each one of your spark plug cylinders. No spark would mean that a spark plug wire is bad.

Step 4:  Remember that each link connected to your spark plugs needs to be hooked up properly and securely. Links include battery cable, ignition wires, and coil wires, not just the spark plug wires.

Step 5:  tug at the link connections from your spark plugs. Then run the test again. Sometimes it could just be a line connection being loose.

Step 6:  Confirm that the end of each of the spark plugs is clean and free of any dirt, oil, or grease deposits. Sometimes, you can just clean them thoroughly and they'll pass the test. But if they still don't test well after cleaning, you'll need to replace them.Watch this to see how to identify a faulty Spark Plug

How to change faulty spark plugs

There are tools you should use when changing spark plugs. A list of them are:

  1. Spark plug socket
  2. Socket wrench extension
  3. Torque wrench
  4. Clean rag or paper towels

Remove the Spark Plugs

Step 1:  Disconnect the negative battery terminal.

Step 2:  Remove any covers. This should be done if there is any.

Step 3:  Vacuum, blow out and clean the area around the spark plugs. This will prevent dirt from entering the spark plug pocket or the engine.

Step 4:  Remove the spark plug boots one at a time. The engine fires in a specific order, and it’s paramount to retain that order, so as you go, use a labeling method such as masking tape to mark which wires go to which plugs.

Step 5:  Remove the spark plugs one at a time and inspect for damage, build-up, or foreign materials.

Inspect the Spark Plugs

  1. All spark plugs will be slightly darkened with black or brown coloring as part of normal wear and tear. However, look for carbon build-up, oil, or gasoline on the plug. If any of these are present, bigger issues that need further diagnosing could be the causes.
  2. Check the center electrode. If it is still relatively even and correctly shaped, it might not need replacing (However, spark plugs are inexpensive and vital to a car’s health, so be sure to replace them within the specified maintenance window, regardless of how the plug looks).
  3. If the plug is young and you decide to keep it, run a check on the spark plug gap with a gap measuring tool. Check the manual for the specified gap and adjust the gap to specified requirements. When closing the gap, do not hit with a hammer or on a directly hard surface. Lightly tap on something like a soft rug or on a towel over a hard surface.
  4. If you’d like to clean the spark plug of dirt, lightly rub with a non-metallic brush, spray it with brake or carburetor cleaner, and dry it.
  5. If the plugs are bad or too old, dispose of them and replace them with new plugs to avoid any mix-ups.

Installing New Spark Plugs in automobiles

Step 1:  Using a plug starter or the socket extension (spark plug sockets typically have magnets or rubber boots to hold the spark plug), screw in the new plugs using bare hands back into the engine. If it feels difficult, pull it back out and try again. You do not want to cross-thread the plug or over-torque.

Step 2:  Confirm the torque specification for your vehicle. When this is done, use a torque wrench to tighten the spark plugs.

Step 3:  Reattach the plug covers (if any) to their specified plug mates.

Step 4:  Reconnect the battery’s negative.

How Often Do You Need To Change Spark Plugs in Automobiles?

On average, you should change spark plugs in automobiles every 30,000 miles, but this could fall between 20,000-40,000 depending on the vehicle.

Read the owner’s manual for specific information about your car, and use your judgment when checking the plugs to determine if they need to be replaced. If the plugs are corroded, it’s time to change, and here is a great read to jump on if you want a spark plug buying guide.

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