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Understand How To Read The Spark Plug Color

Understand How To Read The Spark Plug Color
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Your car will show many warning signs when there’s a problem with the spark plug. A light tan or gray is the normal spark plug color, but it’s a red flag when you spot a different hue.

It does the job of igniting the air and fuel mixture in the cylinders by providing sparks. Your automobile keeps moving on the road because of the constant ignition. So, you may well understand the importance of this device in keeping the engine running.

How To Read The Spark Plug Color

A healthy spark plug will have a little bit of electrode erosion but no abnormal deposits while the color would be a light tan, gray, or brownish. It indicates the optimal operating condition. What will be the spark plug color when it’s undergoing some problems? Let’s have a look:

No Color

spark plugs
You have to understand the color differences to determine the real problem.

If one or more of these devices do not have a dark brown color or are not colored at all, it suggests that the plugs are not firing at all. A working component must collect some deposits and have a different tone than the original shade. If it happens, you should check the fuel or ignition.

Ashy Coating

When the center or ground of the spark electrodes is covered with a layer of ash-like substances, you have to check for an oil leak or the quality of the fuel. The build-up will grow over time and fill in the blank space between two electrodes eventually, causing a misfire. So, if you face this issue, check for a leakage or change the oil to the higher grade one.

Black Deposits

If your engine shows poor starting and misfires, check the spark plug color immediately. You can call a blackish build-up at the top as dry or carbon fouling and oily appearance at the bottom as wet fouling. A clogged cleaner or carburetor, a leak in the vacuum, or the plug’s improper heat range is the probable reason of the first problem while the second one may result from a compromised head gasket or an issue in the valvetrain.


Glazed White Appearance

Spark Plug Color
You can avoid major damage should you detect the problem quickly.

If you frequently face the issue of power loss at high speeds or when the engine load is high, look at the insulator to see if it turns silvery white. You may also find a worn out electrode and minor black deposits. It’s the result of spark plug overheating that may arise from a thin mixture of air and fuel, a vacuum leak, or a poor cooling system.

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A Green Shade

It’s the sign of heavy oxidation and leads to poor engine performance because of the gap in creating sparks. We know that there’s lead in the gasoline. This material creates some chemical reactions with the components in the electrodes and causes corrosion and erosion in the plugs.

Yellowish Brown Deposits

When your engine misfires under hard acceleration or at high-rpm, look for a build-up of this color on the insulator nose. The name of this condition is lead fouling, and it appears when the fuel contains too much lead.

  1. Kathreena Maidang says

    My car has been failing to start even though I’ve just refilled the battery water.

    After reading this, I’m now going to check the spark plug for possible black deposits.

    This information has been very helpful.

    Thank you.


    1. Trang Tran says

      Arigatou. Thank you. Your comments encourage us a lot.

  2. Kabogor says

    Thanks for the instructions. Keep updating us.

    1. Trang Tran says

      Thank you. We will provide more useful information like this. Stay tuned

    2. Reuben says

      I really value these tips. Thanks alot for them and share more with us.

  3. Albert says

    Good tips

    1. Trang Tran says

      Thank you. We will provide more useful information like this. Stay tuned

  4. Victor musonda says

    Slowly am coming a professional mechanics through this page thanks.

  5. james kiama says

    mine i changed plugs last week and as we are speaking,the car has no power(pulling)and fuel consumption is more than normal.thanx

  6. felix mitchell says

    thanks for the tips…

  7. Mudenda Never says

    My engine won’t start. I checked plugs ad discovered they are all wet. Could it be that the coil are not functional. I even bought new plugs. Same problem. It’s a 4e- fe engine. Help

  8. Geoffrey Sembs says

    Thank you so much for sharing with us this important piece of information. I appreciate so much. it will help me for many years to come. Thanks and Compliments of the season.

    1. Saiyad S Ali says

      What is insulator. I think I had problem under Glazed White Appearance . A very good advices to know your vehicle.

  9. Peter says

    Thanks for the updates. I am learning a lot about cars. Arigatou gozaimasu.

  10. Amos says

    For how long am i supposed to change spark plugs for passo sette

  11. Lenzki says

    Thanks for the car looses power at the second gear,i’ll now check on the spark plugs

  12. Jacob M. says

    Very informative. Thanks for such great lessons. Knowledge os power.

  13. Unruly boss says

    My toyota bus is giveing me a problem. When i reve it hard it does loose compression could it come from the plugs

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