Blog Car Care Advice How To Change Spark Plugs (A Step-By-Step Guide + FAQs)
Car Care Advice

How To Change Spark Plugs (A Step-By-Step Guide + FAQs)

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Spark plugs are vital to keeping your car running smoothly. 

They’re responsible for the electric spark that ignites the air fuel mixture in the combustion chamber. This is why it’s crucial to get routine spark plug replacements.

You may be thinking, can you DIY your spark plug replacement? 
And if yes, how can you change spark plugs?

In this article, we’ll go over the detailed procedure of changing spark plugs. We’ll also look at some helpful tips when replacing spark plugs and answer some FAQs

This Article Contains: 

Let’s begin! 

How To Change Spark Plugs (Step-By-Step Guide)

Spark plugs should be inspected routinely to ensure they’re in good shape. And if you ever experience faulty starting or find a worn-out old plug, it’s best to get a prompt replacement to avoid further damage. 

But how do you do that? 
Let’s take a look:

  1. Gather The Supplies
  2. Disconnect The Battery 
  3. Clean The Engine
  4. Locate The Spark Plugs In Your Car
  5. Remove The Spark Plug Wires Or Coil On Plug 
  6. Unscrew The Spark Plug
  7. Prepare The New Spark Plug
  8. Repair The Spark Plug Wires And Clean The Plug Threads
  9. Install The New Spark Plug
  10. Reconnect The Battery And Test Run Your Vehicle

Note: If you’re not confident about handling the repairs, it’s best to let your mechanic take over. Incorrectly installed spark plugs can lead to rough idling, reduced fuel efficiency, damage to the combustion chamber, and even cause spark plug failure. 

Step 1: Gather The Supplies

Changing your vehicles spark plugs can be tricky. 
Here are the tools and other items you’ll need for the replacement: 

Step 2: Disconnect The Battery 

Before attempting any repair or replacement on your vehicle, always ensure your car battery is disconnected

Start by parking your car on a flat, dry surface. Open the hood and locate your car battery. Then, use an adjustable wrench to remove the negative terminal of your battery first, followed by the positive one.

Step 3: Clean The Engine 

The next step in getting a spark plug replacement is to prep your engine and clean it. 

Remove the engine cover if your combustion engine has one. Blast compressed air to clean the surface. This will prevent dirt and debris from getting into the spark plug hole and the engine’s cylinder head.

Label any vacuum hoses you may remove so you won’t misplace them. 

Step 4: Locate The Spark Plugs In Your Vehicle

Under the hood, you’ll find 4-8 wires leading to different points in the engine compartment. The spark plugs are located at the end of these wires, under the spark plug cap. They sit on the lid of the combustion chamber and screw into each cylinder head. 

Your engine may also employ coil-on-plugs (COP) instead, which don’t use a spark plug wire (spark plug lead) as the coils sit directly on top of the plugs. 

Pro Tip: Label the corresponding spark plug wire to the cylinder head, so you don’t mix them up while replacing spark plugs. 

Step 5: Remove The Spark Plug Wires Or Coil-On-Plug 

If your car uses a COP system, release the electrical connector from the ignition coil by gently pulling it up. Take the wiring connector off the coil. COPs have a detachable rubber spark plug boot and springs. If the spark plug boot doesn’t come off the spark plug with the coil, use needle-nose pliers. 

If your vehicle doesn’t use COPs, you’ll find a spark plug cap (plug boot) attached to the spark plug lead and the plugs. In this case, you can use a spark plug wire puller to take out the plug boot.

Note: If you have spark plug wires, remove only a single spark plug wire from one plug at a time. That’ll help you connect the right wire to the right spark plug during replacement. If you have a coil-on-plug (COP), disconnect the coils and set them aside in a safe location.

Step 6: Unscrew The Spark Plug

Next, you’ll need to use a spark plug socket to remove the faulty spark plug from the engine. 

Use a socket wrench to turn the old plug about half an inch in an anti-clockwise direction. You can use a small amount of penetrant liquid to loosen up the threads and wires of old spark plugs. 

If the faulty spark plug seems stuck, gently try to work it out in a back-and-forth motion using the spark plug socket.

If you notice consistent resistance, reach out to your mechanic for help. Using a lot of force to unscrew a bad spark plug can damage the threads and cost you a fortune in repairs.

Step 7: Prepare The New Spark Plug

Once you remove your bad spark plug, you’ll need to prep your engine and new spark plug for installation. Ensure you have the right spark plug set by consulting your vehicle manual and mechanic.

One important step in spark plug maintenance is the spark plug gap. 
Modern spark plugs are pre-gapped, meaning you don’t need to set the gap with a spark plug gauge (feeler gauge) when installing them. 

But if you need to gap them, you’ll need to follow the manufacturer’s specs.

Here’s a general guide to setting the spark plug gap: 

Step 8: Repair The Spark Plug Wires And Clean The Plug Threads

Before you install a new plug, you’ll need to repair any worn-out spark plug wire or coil pack and clean the spark plug threads. Replace any old spark plug wire with a new one. Use a wire brush to clean the wire terminal. 

Rub some anti seize lubricant or dielectric grease along the spark plug threads. This will prevent the spark plug from getting stuck in the cylinder head. You can also apply some dielectric grease inside the plug boot to prolong their efficiency and make their removal easier. 

Step 9: Install The New Spark Plug

Once you have your spark plug gap set, you need to install the spark plug using a torque wrench. Gently start screwing the plug clockwise in the spark plug hole, ensuring the threads are correctly mated. Tighten the spark plug to the manufacturer’s specifications. 

Note: As a rule of thumb, give no more than an additional quarter turn after hand tightening.

Reinstall the ignition coil or plug wire to each spark plug.

Next, reinstall any bolts your engine may have. Make sure the necessary wiring connector and other components are reattached. 

Repeat steps 5 to 9 for the remaining spark plugs.

Step 10: Reconnect The Battery And Test Run Your Vehicle

Reconnect the battery — first, the positive terminal, followed by the negative terminal. 

Once done, test run your vehicle to check if your spark plug replacement was successful. Your Check Engine Light should also turn off at this point. 

You now know how to change spark plugs. 
Let’s also look at some things to keep in mind when replacing spark plugs. 

6 Tips When Changing Spark Plugs

Here are some tips to help you with spark plug replacement:

1. Always work with a cool and clean engine. Wait for at least 30 minutes before you handle the engine for repairs, and get rid of any debris around the work area. 

2. Never downgrade spark plugs. If your car comes with a long-life plug or iridium spark plug, avoid using conventional spark plugs

3. Additionally, always speak to your mechanic before upgrading your plugs

4. When handling any spark plug wire, do not rush. The threads are very delicate and can easily get disconnected from the combustion circuit. Use a torque wrench or a socket wrench to handle spark plugs.

5. Do not over-tighten the spark plugs with the torque wrench or the socket wrench. Always use dielectric grease when reattaching the COP boot or plug wire to a new plug.

6. Most importantly, always refer to your vehicle manual. The vehicle manual is the blueprint for all your car repairs and is your best guide to preventing unfortunate mishaps due to misplaced parts.

Now, let’s go through some FAQs on spark plug changing.

5 FAQs On Spark Plugs

Here are answers to five questions you might have on changing spark plugs:

1. How Often Do I Need To Change Spark Plugs?

Generally, you should change spark plugs every 30,000 miles, but you could also replace them between 20,000 to 40,000 miles, depending on your vehicle usage.

Check out your vehicle user manual to get the specifications of spark plug replacement. At the same time, also use your judgment. If your spark plugs are corroded, it’s time to change them.

2. How Do I Know If My Spark Plugs Need Changing?

If your car is due for spark plug replacement, you’ll notice one or more of the following signs

3. How Much Does A Spark Plug Cost?

For traditional passenger cars, each spark plug can cost from $2-$25. The price depends on the expected life and electrode material. Conventional spark plugs with copper electrodes cost less. Platinum or iridium plugs can cost as much as $25 each.

4. What Happens If I Don’t Change My Spark Plugs?

A couple of bad things can happen if you don’t change your spark plugs at the recommended intervals. 

Firstly, corroded spark plugs won’t produce the required spark, so your engine will have to use more fuel and work harder to produce the required force. This also means you’ll end up spending more money on gas. 

Secondly, if you keep using worn spark plugs, the build-up on spark plugs can lead to an engine misfire which can put unnecessary stress on the cylinder walls. This can even cause dangerous pressure levels to build up and lead to engine failure. 

5. Can I Change My Car’s Spark Plugs On My Own?

It should be okay for someone with decent mechanical knowledge to replace the spark plugs on their own. However, if you’re unsure how to change spark plugs and need help, please reach out to your mechanic. 

For assistance, why not try AutoNation Mobile Service
AutoNation Mobile Service is a mobile auto repair and maintenance solution with a wide range of services and competitive pricing.

Remember, incorrectly installed spark plugs can cause engine damage and affect your car’s fuel efficiency. Your car may have trouble starting and experience poor acceleration, rough idling, and reduced fuel economy, among other problems.

Avoid these issues by letting our mechanics come to your driveway and change your spark plugs for you!

Fill out this online form for a spark plug replacement cost estimate! 

Final Thoughts

Modern spark plugs are very low maintenance. Unlike oil changes, you don’t need to replace your spark plugs very often. Regular replacement schedules and routine inspections should do the trick!   

But when the time comes to switch your old spark plug for a new plug, look no further than AutoNation Mobile Service! We offer convenient online booking and a 12-Month, 12,000-Miles warranty on all our repairs. 

Contact us today to get started!