How to Change Spark Plugs: A Step-by-Step Guide

Vehicle maintenance is something everyone should brush up on, even if you’re not a car person. It helps to know what tasks you can handle at home and what you have the tools for. If you’re interested in learning how to change spark plugs, you’ll be happy to know it’s a straightforward process that almost anyone can follow.

Before we get to the instructions, there are some essential questions to answer, like when to replace spark plugs or how to identify the signs that your vehicle needs new spark plugs. Let’s open the hood and peer in.

How Do I Know When to Replace Spark Plugs?

Spark plug problems aren’t readily apparent unless you know what to look for. If a spark plug is damaged or malfunctioning, it may degrade your vehicle’s performance — but not always in an obvious way. It doesn’t help that a general check engine light on your car’s dashboard signifies many problems, including aging spark plugs.

Some bad spark plug symptoms you may notice if a plug is aging include your car being slow to start, the engine misfiring, idling rough, or issues like poor acceleration and decreasing fuel efficiency. However, many of these symptoms also indicate other maintenance issues. For example, poor fuel efficiency can happen when your vehicle needs a simple oil change. 

That’s why it’s best to rely on a proper car maintenance checklist to identify problems systematically. Tasks like changing an engine air filter, changing the spark plugs, replacing belts, servicing the radiator and changing fuel and oil filters are all part of that maintenance checklist.

In general, the telltale signs you need new spark plugs are related to your vehicle’s performance. If you notice a decline and you’ve ruled out other concerns, it may be time to look at your spark plugs.

How Do Spark Plugs Work?

Spark plugs are designed to move high-voltage electrical currents from the ignition coil into the combustion chamber, which helps start your vehicle when you turn the key or press the start button and keep it going while the engine is on.

In the combustion chamber, the spark plug ignites the fuel or gas, which creates an explosion and helps push the engine’s pistons’ down, sending power and energy to the transmission, which propels the wheels. When the car engine is on, this happens several hundred times a minute. That’s why malfunctioning spark plugs will cause performance issues. They’re not used just once but throughout the duration of your vehicle’s trip.

Since spark plugs rely on your car battery for the proper voltage, you should also check battery health. An optimal car battery ensures healthy spark plugs work more efficiently. Conversely, running your vehicle with damaged or malfunctioning spark plugs puts strain on the battery and drains it faster than usual. Learning how to change your car battery and measure the resting voltage levels are crucial maintenance steps you should probably do every time you replace spark plugs.

How Often Should You Change Your Spark Plugs?

If performance degradation is the primary symptom, it makes sense to change your spark plugs regularly as they become a problem, right? Yes, in fact, it’s actually best to change out the spark plugs before you start to see issues. 

Benefits of changing your spark plugs include:

• Improved vehicle performance and engine idling.
• Improved fuel economy.
• Smooth and less challenging vehicle startups.
• Less harmful emissions because spark plugs improve performance and gas mileage.

That is why most vehicle tune-ups include changing the spark plugs. Generally, consider replacing them at least once per year for each vehicle, certainly every couple of years or when you notice performance declining.

If you don’t service your vehicles and take them to a local mechanic or garage, they should be able to recommend a suitable schedule for replacing your spark plugs.

What Is the Average Spark Plug Replacement Cost?

The price of spark plugs varies from vehicle to vehicle. If you’re paying a mechanic, parts and labor costs also vary. You can expect to pay anywhere from $50 to $500 or more, depending on the vehicle and engine complexity and the spark plug types. For instance, with V6 and V8 engines, the spark plug replacement costs will be higher than those of a standard four-cylinder engine.

The size or type of engine determines the number of spark plugs in your vehicle. Typically, a four-cylinder engine has four spark plugs, a six-cylinder engine has six — a V6 has six — and so on. Boxer engines have four spark plugs, while rotary engines have three.

There are different types of spark plugs, including copper, silver, platinum, double platinum, and iridium, with the latter type being the most expensive — prices range from about $30-$100 each. The more expensive materials tend to offer unique conductivity and varying performance and so those types of spark plugs are used in high-power vehicles. However, platinum and iridium spark plugs last much longer — about four to seven years, respectively.

Should All Spark Plugs Be Replaced at Once?

Ideally, yes. All spark plugs should be replaced to ensure similar life cycles. A misfiring or malfunctioning spark plug can put a lot of added stress on other engine components, including the other spark plugs.

Consider replacing components like spark plug wires, oxygen sensors, coil packs or the fuel filter. All of these engine components affect the performance of the spark plugs.

In an emergency, replacing the malfunctioning spark plugs is okay, but you should know that it may affect the engine’s performance.

How to Remove Old Spark Plugs: A Step-by-Step Guide

Before getting started, there are some tools you may need:

• An old towel or rag
• Mechanic’s gloves
• Goggles or protective glasses
• Compressed air
• A pair of ring nose pliers
• A full socket wrench set, including a spark plug socket
• A socket extension, depending on how deep the well holes are

1. Make Sure the Vehicle Is Off and the Engine Is Cold

This will prevent the engine from burning you, as all components get very hot when the vehicle is running. Also, wearing a pair of mechanic’s gloves is a smart idea.

2. Disconnect the Battery

Unplugging the battery prevents it from shocking you, including components that may be powered, like the spark plugs. Technically, they wouldn’t have power while the vehicle is off, but it’s better to be safe.

Pro Tip: While not necessary, it’s beneficial to clean the surface of the engine and around the spark plugs with a throwaway towel. Once they’re removed, an open hole will be exposed, and if anything gets into the engine chamber, it could cause damage. Keeping the area clean helps prevent this.

3. Identify and Remove the Ignition Coils

The ignition coils are wire-like components attached to the end of each spark plug. They help transfer the electricity when the engine is on. 

To remove them, grab the boot (the cover) with one hand and pull gently until it’s removed. It takes a firm hand, but you must still be careful. Do not pull the coils by the wire, as you may cause damage. If the boot is too difficult to remove by hand, which sometimes happens, you can use a pair of ring nose pliers to make it easier.

4. Remove the Spark Plugs From Their Housing

With the coil removed, the spark plugs are exposed. You’ll need to remove them from their housing by firmly grasping the available top portion and gently turning them counterclockwise. As they’re located deep in the exposed hole or cavity, this may seem difficult. Use a spark plug socket to remove the spark plugs from the well. The special socket is lined with rubber to prevent damage to the ceramic shell of the spark plugs.

Take it slow, and don’t allow debris to fall into the exposed hole. You can use compressed air to blow out debris before removing the old spark plugs.

How to Install New Spark Plugs: A Step-by-Step Guide

Assuming you followed the first portion of the guide to change spark plugs, now we can install new ones. You should keep the same tools handy. 

Here’s some new or additional gear you might need:

• Replacement spark plugs
• Anti-seizing lubricant, if required
• Dielectric grease
• A spark plug gap tool

1. Compare the Old Spark Plugs to the New Ones

Before installing, compare the old and new spark plugs to ensure they are the same size. Although there may be minor design differences, the size should match. Installing the wrong size plugs could damage your engine.

2. Make Sure the Spark Plug Gap Is the Correct Size

Next, we must ensure the spark plug gap is the correct size. This is the area at the top of the plug where the spark is created. If it’s too wide, there may be no spark at all, or your vehicle’s performance will suffer. If it’s too small, there’s a chance the ignition won’t start, or the spark will be weak.

Pre-gapped plugs should also be checked. It’s possible the measurements were affected during shipping and handling or when the packaging was handled at the store.

You should be able to find the correct gap measurements in your vehicle’s owner’s manual or by referencing the emissions sticker attached to your car (under the hood). You may also be able to look it up online.

Use the gapping tool to check the measurement and pry open the plug as needed. If you need to close the gap, press the top hook firmly and evenly on a hard surface until it’s in the correct position.

3. Optional: Apply the Lubricant or Anti-Seize to the New Spark Plugs

Spark plug anti-seize is a lubricant you apply to the plug threads to ensure the unit doesn’t get stuck, making it harder to remove later. 

You only need enough to coat the threads, and it should be evenly spread without getting any on the rest of the plug. Avoid thick globs, and you don’t want any near the gap at the top. It’s best to wear gloves while applying so you don’t get any on your skin.

Pro Tip: Some newer vehicles don’t need anti-seize lubricant. Review your car’s owner’s manual, or check with the spark plug manufacturer, and they’ll tell you if lubricant is required.

4. Apply Dielectric Grease

Also called silicone grease, dielectric grease is an insulator ensuring proper heat dissipation. It also prevents moisture from entering the spark plug boot and causing corrosion. 

Place a small amount on the bottom ceramic portion of the spark plug without spreading it anywhere else. Apply a glob and then spread it evenly with your fingers around the cylinder. You may also place some grease inside the spark plug boot. It’s easy to apply using a cotton swab.

5. Install Your New Spark Plugs

You must use just the right amount of finesse to install the new plugs. Tightening them too much could damage the threads or break the plug or housing. Not tightening them enough could cause them to come loose during operation and damage the engine.

Use the spark plug socket, place the new plug into the socket, and then, with an extension attached, lower it into the well and tighten it by hand. Never use a power tool to tighten your spark plugs. When the plug is too tight to finish with your hands, use a socket wrench to complete the last half-turn. Do not over-tighten the plugs.

6. Reconnect the Ignition Coils or Boots

Finally, reconnect the ignition coils or boots to the top portion of the spark plugs, sealing up the wells. It should be pretty straightforward. Press them down into the well until you hear a click.

You’ll also want to reconnect your battery if you follow the top portion of this guide.

Start It Up and Take a Drive

Now that you know how to change spark plugs in your car and you have new ones installed, it’s time to start your car and take it for a drive. If you have noticed some of the performance-related spark plug problems, note how much better your vehicle operates now. Those issues should not persist unless there’s another maintenance concern.

It’s also a great idea to keep track of fuel economy and gas mileage after you replace your spark plugs and old components. That way, you know when your car is using fuel more efficiently and when things start to decline — which means maintenance is necessary again.