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Know Your Engine – Read Your Spark Plugs

Assorted Spark Plugs

In case your spark plugs are fouled or damaged, various issues may arise such as decreased fuel efficiency, sluggish acceleration, engine misfires, and difficulty starting the engine. If you are facing engine troubles, inspecting your spark plugs is a recommended initial step. Upon examining the spark plugs, you may come across one of the following scenarios:


Normal

Carbon fouled

Oil deposits

Wet

Burned

Worn electrodes

Broken electrodes


Checking the Performance of Your Engine


Inspecting the spark plugs of your engine can provide insight into its performance. This task can be included in the regular maintenance of your vehicle, ATV, lawnmower, or boat, or when you suspect any issues with the engine.


Getting Started


To start, take out the spark plug you wish to inspect. Refer to the provided guidelines for removing a spark plug. Hold the spark plug in your hand and carefully inspect it for any signs of damage. Focus on the end of the spark plug that was inside the cylinder and conduct a thorough examination. You are likely to observe one of the following scenarios.


Normal Spark Plug

Normal spark plug

If a spark plug shows brown or grayish-tan deposits on the side electrode, it is considered normal. Your spark plug is in good condition, and you can proceed to reinstall it.


Carbon Fouled

Carbon fouled spark plug

If you notice black, dry soot on the electrodes and insulator tip, it means the plug is fouled with carbon. This issue can result from a dirty air filter, frequent driving at low speeds, an overly rich fuel/air mixture, or excessive idling. Your mechanic can recommend a suitable replacement spark plug for the damaged one, and you might want to think about switching to a "hotter" spark plug (remember, the higher the spark plug number, the hotter the plug).


Oil deposits

Oil deposits spark plug

If you notice black, oily deposits on the electrodes and insulator tip, it indicates that the plug is fouled with oil. This could be due to oil seeping into the cylinders, possibly passing worn pistons or valve guides. Identifying the source of the leak is crucial, so it's advisable to seek advice from a mechanic. Once the issue is resolved, you can proceed with replacing the spark plug.


Wet Spark Plug

Wet spark plug

If a spark plug is wet, it may be due to the engine flooding, which occurs when attempting to start the engine multiple times without success. You have the option to either clean the spark plugs or allow them to dry naturally.


Burned Spark Plugs


Burned spark plug

If you notice blisters on the insulator tip, melted electrodes, or white deposits on a spark plug, it indicates that the spark plug is running too hot and is burned. This could be due to reasons such as engine overheating, incorrect spark plug heat range, a loose spark plug, incorrect ignition timing, or a too lean air/fuel mixture. In such cases, it is recommended to replace the spark plug.


Worn electrodes

Worn electrodes spark plug

When electrodes are worn out and eroded, it indicates that the spark plug is no longer effective. The plug has been in use for an extended period and should be swapped out for a new one.


Broken Electrodes

Broken electrode spark plug

Incorrect installation of spark plugs, such as breaking or flattening the electrodes, may indicate that the wrong spark plugs have been used. Using a spark plug that is either too long or too short can result in severe engine damage or issues like reduced fuel efficiency and spark plug fouling. Consult your owner’s manual to confirm that the correct spark plug is being used for your vehicle.

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