Don’t Lose Your Spark: How Often Should You Replace Your Spark Plugs?

Spark plugs get their name from the way they ignite fuel in an internal combustion engine. The spark comes when a small gap between two electrodes causes electricity to jump across. 

These jumping electrons cause atoms along the path where the electricity travels to split into oxygen molecules and carbon particles. Carbon combines with oxygen to create more carbon dioxide gas, and hydrogen atoms combine with oxygen to form water vapor. 

These devices can be found inside almost every car on today’s roadways. While most people don’t think about these tiny components too much, you should at least be aware of how often to change them. 

In this article, you’ll learn how often you should replace your spark plugs, how they work, and how to tell if your current plugs are still good. 

What Is a Spark Plug? 

A spark plug provides the voltage needed to start the process of burning air and gasoline together. This mixture creates the energy that drives the pistons attached to the crankshaft. Without a spark plug, no engine would run. 

The spark plug has three parts: A central electrode, which sits at the center of the metal shell; ground electrode(s), which attach to one end of the cylinder; and a resistor wire wrapped around the middle of both. 

When a high voltage electrical current runs through the central electrode, it jumps across a small gap to the ground electrode. The resistance of the resistor wire slows down the flow enough so that it doesn’t arc over to the other side of the gap. As a result, the spark ignites the fuel. 

This whole process takes place very quickly, but the speed varies depending on the type of spark plug. For instance, a distributor spark plug only needs a few microseconds to produce a spark. In contrast, a spark plug used with direct injection engines may take as long as several milliseconds to generate a spark.

How Do Spark Plugs Work? 

If you own a vehicle with spark ignition (i.e., most vehicles manufactured after the mid-1970s), then the chances are good that its spark plugs have a gap ranging from 0.02 inches to 0.04 inches in diameter. Some older models had smaller gaps, while others had larger ones. Regardless, all modern spark plugs use this same basic design. 

Modern spark plugs contain multiple wires because each cylinder in the engine requires different amounts of voltage. For example, the first cylinder might require 500 volts, whereas the second might need 1,500 volts. Manufacturers wrap individual wires around the central electrode and connect them to separate connectors to accommodate this difference. 

Each connector contains either four or eight terminals. The number of terminals per connector depends on the vehicle’s model year. Older models feature four terminals, while newer models feature eight. 

Some manufacturers also include a spark plug called a “spark advance” cable. This device allows drivers to adjust the timing of when sparks occur within each cycle of the engine’s rotation. 

Different vehicles need different amounts of time to complete various steps during the combustion process. Adjusting the timing of when the spark occurs can help improve performance by improving efficiency and reducing emissions. 

Types of Spark Plugs

There are many different types of spark plugs available. They vary based on the following factors:

Gap Size

The gap size is the distance between the central electrode and the ground electrode. In general, this distance decreases as the size of the gap increases. 

However, this relationship isn’t always linear. For example, large gaps tend to wear out faster than small gaps. It’s best to choose a spark plug whose gap matches the gap size of the particular engine being modified.

Wire Material

Wire materials made of iron, nickel, cobalt, chromium, copper, silver, gold, tungsten, platinum, molybdenum, rhodium, iridium, boron, silicon carbide, aluminum oxide, and manganese are common. Each substance offers advantages and disadvantages. 

Iron typically produces the lowest amount of heat, but it wears down fast and cannot withstand extreme temperatures. Nickel is better at producing heat, but it tends to break down easier than other substances under high-stress conditions. 

Cobalt, chromium, copper, and tungsten provide great strength, durability, and heat resistance, but they cost more money. Silver, gold, and platinum are expensive, but they last longer than iron and nickel. Molybdenum, rhodium, iridium, boron, silicon carbide, aluminum oxide, and manganese offer improved heat resistance compared to other substances, but they aren’t as strong or durable. 

Resistor Wire 

The length and thickness of the resistor wire determine how effectively it resists arcing. Short, thin wires burn up faster than thicker wires. 

Thicker wires are stronger than thinner wires, but they degrade quicker when exposed to dirt and debris. Platinum and palladium resist degradation better than other substances. 

Construction Method

Some spark plugs are constructed using a screw thread, while others utilize machining processes. Screw threads allow users to remove the entire component without destroying the rest of the engine. Machined components must be replaced instead. 


Longer wires generally provide more power than shorter ones. Spark plug manufacturers sometimes recommend specific lengths for certain applications. For instance, a person who works on a farm might want to use shorter spark plugs than someone who drives a hybrid automobile. 

How Often Should I Replace My Spark Plugs? 

Replacing your spark plugs once every five years is typical. However, most experts agree that replacing spark plugs sooner could damage your engine. 

Early replacement is bad because it leaves less time for the newly installed spark plugs to fully soak in. Normally, new spark plugs are allowed to sit overnight before installation. If you try to install them immediately, the hotplug holes in the cylinders may not seal properly. 

Another reason is that old spark plugs make contact with the walls of the hole differently than new ones. Old spark plugs may stick to the walls due to fouling. Newer models may leave behind deposits of oil, tar, and other substances that reduce the effectiveness of the plug. 

In addition, old plugs may not fit correctly in the hole. Improper placement can lead to poor airflow and increased wear. Finally, old plugs may not hold up well under intense stress. For example, poorly maintained spark plugs may crack when subjected to sudden changes in temperature. 

How to Change a Spark Plug

Normally, you can easily change a spark plug yourself without having to pay a professional mechanic. Whenever you put your car in a professional shop, they have to bill you for at least one hour of labor. 

This hour of labor will run you about $100 when in reality, it probably only took them five minutes to change the plugs. The following list will show you how to change your own spark plugs so you can save money next time. 

What You’ll Need

  • The new spark plug
  • A spark plug socket
  • Socket wrench
  • Anti-seize grease

Step One

Make sure your car is parked on a flat service and the engine is cool. If you’ve just recently parked, give it about 30-minutes to cool down. While you’re waiting for the engine to cool, clean the engine compartment of any dirt or foreign objects. Air compressors are ideal for this. Cleaning everything out of this area will prevent any dirt from getting into the engine cylinder while you’re replacing the spark plugs. You’ll also disconnect the negative battery cable. 

Step Two

You’ll want to remove any interference items. You’ll find the rubber spark plug wire end and the metal terminal hard to remove from the spark plug. It’s important that you’re careful not to damage the rubber boot. If it feels stuck, try using spark plug wire pliers to help. The metal terminal that connects the plug inside the boot must be taken off at the same time to avoid damage. If it does get damaged, it’s not the end of the world. You’ll need to replace the plug wire if this happens; otherwise, the plugs will misfire. If your vehicle has over 100,000, it’s recommended that you replace the plug wires anyway. 

Step Three

Disconnect the electrical connector from the ignition coil. Push down on the locking tab and disconnect. You might need a small screwdriver to push the tab down. Once the connector is removed, push the bolt down and twist the coil about a quarter turn. Do this back and forth until the seal is broken. Afterward, it should pull right out. Be careful not to damage the boots, or else you’ll need to replace them. 

Step Four

Use the spark plug socket to remove the plugs. Make sure you don’t damage the threads during this step. Blow down into the spark plug well hole to remove any debris. The smallest particles can cause damage to the heads. If you’re having difficulty, place a small drop of the grease near the base area of the spark plug. Wait a few minutes and give the grease time to work into the threads. Slowly begin turning. If it doesn’t budge, turn the plug a half-turn clockwise to spread the grease. Turn back counter-clockwise, then clockwise once more. After some twisting, it should begin to free itself. 

Step Five

Before you install the new plugs, make sure the part number on the plug matches the part number on the box. Check each plug closely for any damage. Each plug should be clean, straight, and have no cracks. The electrode should be in perfect shape with no chips anywhere on the part. Install the new plug, but be careful that you don’t cross-thread or damage the plug, as well as your cylinder heads. When you tighten the plugs, it’s critical that you use the right amount of torque. You can use a torque wrench to check this if you’re unsure. Basically, you just don’t want to overtighten the plug and damage the heads in any way. 

Step Six

Place a small amount of the grease onto the boot and prepare to replace everything. Connect the plug wires back to the corresponding plug. Replace the coil hold-down bolts, and re-attach the electrical connections. You can replace any other components you moved before beginning the installation. Make sure all tools are clear from under the hood of the car, and don’t forget to re-connect your negative battery cable before you start the car. 

How to Tell If Spark Plugs Are Still Good

Many mechanics have a knack for figuring out whether a worn spark plug is worth fixing. One easy way to test the longevity of a spark plug is to look at its color. Blackened or cracked spark plugs indicate that the plug has been damaged. 

However, some metals become discolored even when they appear fine externally. If a black spot develops below a shiny surface, it likely indicates a problem. If you find any cracks or chips, you should consult a professional mechanic. He or she will usually examine the spark plug under magnification and advise you accordingly. 

It’s also possible that the spark plug itself is working normally, but the connection between the wire and the terminal is degrading. If you notice a loss of power or a drop in performance at higher speeds, it could mean that the spark plug has developed a short somewhere between the tip of the central electrode and the ground electrode. This is known as a “high tension spark.” In this case, you should consult a professional mechanic. 

You can avoid this scenario by checking the connections regularly. Look for loose screws, broken wires, corroded contacts, or bent pins. If you see any of these signs, clean the area thoroughly, then check again. 

The steps above may seem complicated – that’s just because they’re explained thoroughly. In reality, changing a spark plug shouldn’t take longer than 15 to 20 minutes. 

Whether you’re changing your spark plugs yourself or taking them to a shop, you shouldn’t neglect this vital part of your car’s system. Proper maintenance helps ensure that your spark plugs perform optimally for years to come. 


Written by Strut Daddy's

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