How to Remove and Inspect Your Car’s Spark Plugs

Years ago, spark plugs became fouled much more quickly than they do today. It was common to need replacements after driving little more than 10,000 to 15,000 miles. Part of the problem back then was that automotive fuel contained lead. Today, with lead all but removed from fuel, spark plugs can last 40,000 miles or more. Some are even advertised to last 100,000 miles (though this is optimistic).
Because the plugs represent a critical part of your engine’s operation (without spark, there can be no combustion), it’s important to change them when they show signs of wear. Neglecting to do so will result in declining performance. Below, we’ll take you through the process of removing and inspecting them.
Gathering Your Tools And Locating The Plugs
In addition to a set of replacement spark plugs, you’ll need access to a socket wrench, spark plug socket, and a few socket extensions. You should also plan to wear safety goggles to protect your eyes from debris.
Lift the hood of your vehicle, and look for wires along the top of your engine. They are made of rubber, and each is connected to a cylinder. If your vehicle’s engine has four cylinders, you’ll be able to see four wires. A 6-cylinder engine will have six wires, and so on. Once you have located them, you’re ready to remove the plugs.
Removing The Plug Wires
A lot of people doing this for the first time are tempted to removed all of the wires simultaneously. It seems simpler to do so. The problem is, the plugs in your engine’s cylinders fire in a particular order. If, while replacing them, you inadvertently mix the wires and cylinders in the wrong order, your engine’s performance may suffer. To avoid that problem, replace them one at a time.
Grasp the first plug wire snugly, twist it, and pull. It should come off easily, leaving the plug sticking out of the engine block. You’ll see the plug’s terminal (the topmost part) and part of the insulator exposed. The next step is to remove the plug.
Removing The Spark Plugs
You’ll need your socket to remove the spark plug from its housing in the block. Slip the socket over the plug (using an appropriate extension), and make sure the fit is snug. Then, attach the ratchet. Gain some leverage and turn it gently counter-clockwise. Apply a little pressure if the plug seems stuck.
Once you have removed the first spark plug, inspect its condition closely. It will provide clues regarding your engine’s operation.
Checking The Condition Of The Plugs
There are several indicators that suggest possible problems. For example, look at the side and center electrodes (located on the opposite end of the terminal). Has black soot accumulated on the tips? If so, you’re observing carbon deposits, which suggest the air-fuel mixture in the cylinder is running rich.
Do you see deposits on the electrodes that appear black and wet? If so, you’re seeing oil. This can mean a few things, but the most common is that oil is leaking past one or both of the valves (intake or exhaust) into the cylinder.
Sometimes, the center electrode will melt. This is more serious than oil leaks or a too-rich air-fuel mixture. A melted electrode might imply your engine is running too hot. It can also mean other things, but it is important to identify the cause to prevent expensive damage from occurring to the assembly.
Another item to note is the gap between the side and center electrodes. The spark that ignites the air-fuel mixture in the cylinder must be able to jump the gap. Over tens of thousands of miles and millions of sparks, the center electrode erodes. As it does, the gap widens. If you notice significant erosion, it’s time to change the plugs.
Fouled, melted, or eroded spark plugs will eventually lead to engine performance problems. If your engine is behaving strangely, check the plugs and replace them, if necessary.