how to read a spark plug

How to Read a Spark Plug

A spark plug is a critical component in the modern combustion engine. Modern gasoline engines heavily rely on this component to ignite the engine by mixing air and fuel in the right ratios in the combustion chamber. Though tiny, this component is mighty as it emits a great deal of electricity across a small gap enough to ignite your vehicle. Now, while that’s the case, did you know that a spark plug can also provide valuable information about your car’s performance? Well, that’s absolutely true especially if you know how to read a spark plug.

But, what if you’re not conversant with spark plugs? Well, in that case, this short guide has done all the homework for you by taking you through a step-by-step procedure on how to read your car’s spark plug.

As we mentioned earlier, a spark plug is a critical component that’s directly linked to the performance of your engine. If the plug is faulty, your engine’s health will automatically be affected leading to poor tuning issues, a drop in fuel economy, and finally, a major engine problem.


How Does a Spark Plug Work and What Causes It to Wear Out?


Before we get to our main topic, let’s first understand the spark plug by briefly discussing how it works, what makes it wear out, and when it needs to be replaced.

Now, just like other components in your car, a spark plug does wear out in normal usage. Since the electrode is the one responsible for creating an electric arc/spark that ignites your vehicle, it’s hence the primary component that wears out in a spark plug.

If you happen to look closely at a spark plug, you’ll notice that one of its ends is narrow and tapered while the other end is bulbous—with a metal rod at the center and a metal hook attached to one side.


What Makes the Spark Plug Wear Out?


Although your spark plug is designed to endure very high temperatures, it will definitely age with time making it difficult for the electrode to generate enough bursts of energy to ignite your car. Now, here are some factors that accelerate the wearing off of the spark plug.

  • Debris Buildup: following frequent interaction between the spark plug and the air-fuel mixture, debris and other oil contaminants can form deposits on its surface causing debris build-up that over time causes pre-ignition of the fuel.
  • Wear and Tear: since spark plugs are exposed to very high temperatures, this over time causes wear and tear on the electrode resulting in inefficiency.
  • Overheating: sometimes, your engine’s cooling system might fail to work optimally causing the engine to run hot. This in return overworks the spark plug exposing it to extreme heat thus reducing its efficiency.


So, How Do You Read Your Car’s Spark Plug?


Now that we’ve briefly discussed some essential points that you need to know about the spark plug, let’s now head straight to our main topic of the day. Now, reading the spark plug simply involves observing its color and condition. In most cases, a healthy spark plug has a light tan color around its tip.

If the tip has any other color or maybe if you doubt its condition, then it simply indicates there’s an issue with the engine, the ignition or the fuel system. With that said, below are some steps that will help you learn how to read the spark plug.


Step 1: Remove the Spark Plug to Inspect It

Before you remove the spark plugs, it’s a good practice that you first read your car’s service manual to determine the location of the plugs and the right tools to use when pulling them out. Now, depending on the model of your vehicle, you may require an extension bar and a ratchet socket drive wrench to remove the plugs out of their sockets.

If you wish to inspect the plugs after driving your car, it’s recommended that you first spare some time to let the engine cool down. Remember, when the engine is hot, the spark plugs too are extremely hot causing them to bind in the cylinder. This in return makes it difficult to remove them.

Tip: When removing the plugs, do it one at a time instead of removing all of them in one go. This helps to avoid confusion as each plug must be retrieved to its respective slot. If a spark plug has a problem, make sure that you replace it and if you don’t have a replacement, fit it back to its respective slot and don’t forget to note its slot and cause of the problem.

Step 2: Check for Soot

If you’re a new car owner with little or insufficient knowledge about automotive parts, then it’s wise that you use a new separate spark plug for comparison purposes. At least this will make reading the spark plug a lot easier.

Now, if you’re inspecting your spark plug for soot, what you’ll be looking for actually is deposits of black soot on the electrode and the insulator tip. If there’s soot on the spark plug, then it simply means that your car has a dry air filter or the engine is experiencing a high air-fuel mixture.

In case the black soot is caused by a rich fuel-air mixture, then you don’t have to replace the spark plug but instead, you should adjust your car’s carburetor.

Note: a carbon-fouled spark plug can also be caused by lengthy idling of the engine or driving at long distances at very slow speeds.

Step 3: Look for Any White Deposits

Any white ashy-looking deposits on the spark plug’s electrode or insulator mean that your engine is running on excessive oil or there are potential fuel additives. This problem can also be caused by leaking oil somewhere in the engine or potential issues on the valve guide seals, the cylinders, the oil control rings or the pistons.

Unlike a carbon-fouled plug that’s usually dry, an oil-fouled spark plug is moist when touched. Now, although this serious problem can be remedied by replacing the spark plug, it’s advisable to have an engine specialist diagnose the problem and repair the oil leakage as replacing the spark plug will only mean that you’ll keep having the same problems over and over.

Step 4: Check for Tan Blisters or Signs of Burning

Here, you will notice white or tan blisters that resemble bubbles on the insulator tip of the spark plug or you might see some signs of burning. This is a clear sign of overheating in the engine’s system and is mostly caused by insufficient engine coolant.

It can also be caused by leakage in the engine’s cooling system as leakage can prevent the coolant from circulating properly leading to overheating. Other causes of blistering in the spark plug are loose plug, incorrect ignition timing, or lean fuel-air mixture in the combustion chamber that’s caused by using fuel with lots of additives.

To remedy this problem, use spark plugs that match your car’s make and model and have a mechanic or an engine specialist check and repair any vacuum leaks.

Step 5: Check for Any Black Spots

If you happen to see black pepper-like spots on the nose of the spark plug, then there’s a high possibility of light detonation. Additionally, if you notice cracks or signs of chipping in the spark plug’s insulator, then there’s an even bigger problem at hand.

Detonation is a serious problem that can cause irreversible damage to the engine’s pistons, oil rings, cylinders, and intake valves if it’s not remedied immediately.

To solve this issue, simply have a mechanic perform a full diagnosis of your car’s engine. Also, make sure the replacement spark plugs you use have the right heat range that’s recommended for your vehicle. Check your fuel and the oil to ensure that they’re in the correct octane levels recommended for your car’s specific engine.

Step 6: Check for Broken Electrodes

Finally, you need to check your car’s spark plug electrodes to ensure that they’re not worn out or broken. By comparing it to anew spark plug, the electrode should be smooth without any dents on the surface.

To identify a damaged spark plug, you won’t see the “hook” section of the electrode. This condition is usually caused by using incorrect spark plugs and is only remedied by replacing the spark plug altogether.

Note: if the spark plug is longer than normal, it might damage your car’s engine and when it’s short; your car’s fuel consumption might be higher than normal.


Final Verdict


If you ever experience problems such as hard vehicle start, reduced performance, high fuel consumption, and unusual rattling noises, then it’s clear that your car has a serious spark plug problem and it requires immediate assessment.

Away from that, reading your car’s spark plug is very easy as it requires you to have a brand new plug for comparison purposes. For those who cannot assess their car’s spark plugs by themselves, then it’s recommended that you seek help from a mechanic or an engine specialist to have them diagnose the problem for you.

For those worried about the long hours, it takes to complete an engine assessment process, then you can have a car monitoring system do the job as they’re able to pinpoint various engine problems much faster.

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