How To Read Your Spark Plugs Like The Pros

Automotive Articles

There are plenty of ways to tell how your engine currently performs. One of those ways includes taking a good look at the wear and tear on your car's spark plugs. Being able to examine the appearance and condition of your spark plugs can give you a leg up when it comes to diagnosing a variety of engine problems. The following shows you how you can do just that and what you should look for when reading your spark plugs.

The Life and Times of a Spark Plug

An engine needs three things to function: air, fuel and an ignition source to detonate both within the combustion chamber. Spark plugs provide the spark needed to set off the fuel/air mixture in the cylinder. At one end, the spark plug is connected to a lead from the ignition coil. The coil must deliver enough voltage through the central electrode to overcome the dielectric constant of the fuel/air mixture. When it hits the ground electrode, the spark detonates the mixture and creates the carefully controlled combustion needed for proper engine operation.

Just like your belts and fluids, spark plugs are wear items that require replacement every so often. Most standard copper plugs can last 15,000 to 20,000 miles (24,000 to 32,000 kilometers) between replacements, while the latest iridium spark plugs are capable of surviving 120,000 miles (193,000 kilometers).

Looking in All the Right Places

To access your engine's spark plugs, you'll have to grab a ratchet fitted with the appropriate socket and remove the spark plug from the cylinder head. As a simple tip, you may want to remove and reinsert each spark plug one by one to avoid crossing up your spark plug wiring.

Once the spark plug is out of the cylinder head, simply take a look at the bottom of the plug and look for the L-shaped ground electrode. Beneath it will be the center electrode, which will be encased within the porcelain insulator. This is what you'll look at when

Reading Your Spark Plug's True Colors

As you can imagine, the forces spark plugs are subjected to throughout their lifespan can drastically change their appearance over time. On an engine operating in peak condition, the spark plug's central and ground electrodes will have a light gray or brownish color, with no signs of erosion, fouling or carbon buildup.

If you see any of the following when checking your spark plugs, then there may be underlying mechanical issues that should be resolved as soon as possible:

  • Carbon fouling – The spark plug appears black and full of carbon deposits. This is usually caused by oil leakage through the piston rings or poor fuel quality.  
  • Oil fouling – You'll see wet oil on the plugs. This means oil is somehow making its way past the piston ring or valve guides. It's usually a sign of a badly worn engine.
  • Overheating – The insulator tip takes on a glazed or glossy appearance, usually due to improper ignition timing or a lean fuel/air mixture. It can also be caused by low engine oil or coolant or even a spark plug operating well above its heat range.
  • Gasoline additives – You may see ash deposits on the electrodes or a pinkish color on the insulator. This is usually caused by various gasoline additives.
  • Physical damage – A bent or broken ground electrode, a broken central electrode or broken insulator could point to a number of problems. Pre-ignition or detonation can cause these problems, as well as the entry of a foreign object into the combustion chamber. A spark plug that's too long for the cylinder head can also be damaged once it comes into contact with the piston.
  • Splash fouling – The spark plug accumulates "spotted" deposits after the vehicle has undergone a long delayed tune-up. Combustion byproducts can come loose from the valve heads and piston crown and end up on the spark plug insulator.
  • Erosion – This usually occurs when the spark plug is well past its useful life. The longer it remains in place, the more voltage is needed for the plug to operate properly. The vehicle will experience poor fuel economy and engine performance over time.

Checking your spark plugs on a regular basis can help you determine how well your engine functions and whether it requires early auto tune ups by a trained and experienced mechanic.


8 July 2015

Emergency Car Care for Young People

When my daughter packed up and left for college, I worried that her car would get her from point A to point B with some sort of problem. I was right to worry. Her car ended up at a mechanic's shop miles from home with extensive repair work needed. Even though the car was fixed promptly and she arrived at her destination on time, I was worried. After that, I created a blog for other young people who are faced with car problems while traveling. My daughter didn't even know how to change a tire! With the research I compiled and a little practice, she can now change her tire and more.