The Whats and Hows of Spark Plugs

September 23, 2022 The Mechanic Doctor

There are at least half a dozen times your car will tell you when the spark plugs need changing. Rough idling, trouble starting the engine, misfiring, painfully slow acceleration, and unusually high fuel consumption are just some of the cases where worn spark plugs won’t allow the engine to work as it should.

To restore engine performance, a set of replacement spark plugs can put the life back in your car. That said, it’s important to understand their role, how they work and get familiar with the different types available. So, without further ado.

Why Spark Plugs Are Important

The role spark plugs play is vital, and without them, your car won’t be going anywhere. They’re tasked to provide the spark for the air and fuel mixture in the combustion cycle. This needs to be at the right ratio and compression and delivered at the right time. Then it’s the plugs that take the stage.

These small engine parts are located in the cylinder head and work by redirecting extremely high voltage from the vehicle ignition system (in the vicinity of 30000 Volts) to create a spark that ignites the air and fuel mixture needed for pushing pistons downwards and turning the crank. They do this hundreds of times a minute while facing corrosion from combusted gases, very high pressures (around 700 psi), and in working temperatures ranging from 150 to well over 3500°F. So yes, they need to be built tough.

Parts in Spark Plugs

Spark plugs consist of several parts, each having a crucial role in delivering voltage to create a spark. Plugs are elongated and cylindrical in shape. At the top is the terminal that connects the plug to the ignition system and delivers the needed high voltage. A central electrode connects to the terminal by an internal wire and runs the length of the plug, and ends in a copper, nickel, chromium, or tip made of precious metals.

To insulate the terminal and central electrode against high voltage and excessive heat and prevent flashover of current, there is a ceramic insulator. Resistors lining the insulator prevent ignition noise during sparking and protect other vehicle electrical components (for example, radios) from electromagnetic interference.

Below this is a steel hex head that grounds the plug to the cylinder head, helps dissipate heat, and slots into the cylinder by tightening with a socket wrench. A galvanized and chrome-plated gasket prevents corrosion from expanding gases. The spark plug then terminates into a ground or side terminal. The gap between the central and ground terminal is where the spark is created.

Spark Plug Heat Ranges

“Heat range” refers to the heat dissipation range of spark plugs. High heat range or cold type spark plugs are other names for plugs that disperse heat well. Low heat or hot type spark plugs are those with a low level of heat propagation.

The design of individual parts determines the type of plug. This includes the length of the insulator ‘nose’, the overall surface area, the metals in the central electrode, and the position of the insulator tip. The heat range of spark plugs means different plugs are used for different engines.

Hot spark plugs are found in many passenger vehicles with more insulation to remove heat slowly. This is necessary to prevent carbonization (or the buildup of carbon deposits). Here the tips remain hotter for longer.

Cold spark plugs are found in performance, and high-revving engines since these operate at higher temperatures. These plugs transfer heat faster due to the shorter insulator, and tips remain cooler as a result.

Choosing a plug that is too cool means more carbonization that will eventually lead to misfires and the engine stalling. Adversely, plugs that are too hot can lead to premature wear from overheating, pre-ignition and knocking issues, and higher fuel consumption.

Types of Spark Plugs by Materials

Copper

Spark plugs are also differentiated by the metals that make up the central and side electrodes. This will affect overall performance, longevity, and efficiency.

The cheapest and most common are copper spark plugs, with copper incorporated into the electrodes and nickel alloys used in the metal outer. They can run cooler, so are good for performance applications, especially in turbocharged engines with high compression ratios. And they’re also the type of plug found in older carbureted engines with traditional distribution caps. Downsides are the high rate of wear in the nickel outer, leading to an average lifespan of around 20,000 miles.

Platinum

Platinum spark plugs are similar to copper plugs, but the center electrode is shielded by a platinum outer instead of nickel. As a result, they better handle high heat and are rated for 100,000 miles. The heat advantage also means lower carbonization and fouling. There are two variants – single and double platinum plugs, with the latter having a platinum case surrounding both the center and side electrodes.

Iridium

In comparison to platinum, iridium is considerably stronger and has a higher melting point. Additionally, because the central electrode on iridium spark plugs is smaller, less voltage is needed to produce a spark, improving efficiency. These attributes mean that they will last the longest of any type of spark plug. If your car is already fitted with iridium plugs, then these are the replacement spark plugs to get if you don’t want to downgrade engine performance.

Signs of Spark Plug Failure

Spark plugs with damage to the electrodes and signs of carbonization will result in reduced engine performance. In addition, those that aren’t rated for the high heat will need to be changed sooner. Here are the typical signs that you need replacement spark plugs:

Difficulty starting the engine – Worn, overheated, and damaged spark plugs won’t have enough juice for the initial spark to get things going. Besides flat batteries, this is the most common problem in cars that just won’t start.
Misfiring – Misfiring is essentially the inability of the engine to combust the fuel and air mixture. During a misfire, there can be sudden jolts and vibrations, and the reason that the ride is uncomfortable. This will ultimately affect performance and increase fuel usage.
Lower gas mileage – If the car computer shows that you’re using more gas than usual, this can be down to spark plugs that are dirty or fouled. And this can be the result of a single spark plug not working properly.
Lack of acceleration – Cars that take longer to accelerate, even with the foot firmly down, may have issues with the plugs. Damaged electrodes mean that sparks aren’t produced at the required strength and difficulty in getting the engine and vehicle up to speed.
Rough idling – Excessive vibrations and unpleasant sounds when the engine is idling can be a sign of fouled or faulty spark plugs.

Buying Replacement Plugs for Your Vehicle

Spark plugs are cheap and simple to replace, yet driving with ones that are at fault can lead to more serious problems down the road. Go for replacement plugs recommended by the manufacturer and something you’d find in the owner’s manual. Online vehicle databases with car make, model, engine, and production year can also prove handy if the owner’s manual is missing.