How to tell if spark plugs have gone bad?

Back in the early days of automotive industry cars had a lot of ignition parts, but these days its more simpler, like we no longer have spark plug wires. But regardless of how exotic the car is, all cars have spark plugs. In this article we will show you how to read a spark plug, how to tell if its gone bad or if there is some more life left in it. You can also determine the condition of your engine by looking at the spark plugs.

Normal Wear

Have a look at the spark plug in above picture. What you can notice is that the center electrode has worn away. This is normal wear and you don’t have to worry about your engine. Your engine is in good health but you have run too many miles on those spark plugs, so its time to change.


Black & Dry

Now this spark plug is black at the top of the electrode and is also dry like charcoal. If this happened only on one cylinder of the engine then that can mean that you have a leaky fuel injector. If this black stuff is on all cylinders then your engine most probably have overall fuel control problem.

Clean Plug

If your plug in spotless clean and cleaner than all other plugs in the engine, that probably means that your car’s coolant is getting into the cylinder and is steam cleaning the tip of the spark plug.

Slight Discoloration

This is what you should expect from a normal plug which has not run out of life yet. There is slight discoloration, the electrode have worn out evenly and there are no visible deposits. If you see it like this, then just put it back in the engine and you’re good to go.

Sandy Electrode

If the spark plug has dry and sandy looking surface that has enveloped mainly the outer electrode, then its a clear symptom of bad valve seals. It means that oil is leaking into the engine and is coming around value seals or gates.

Greasy Plug

This is the one you should fear. You can see that the end of the plug is filled with black gunk and its oily and greasy. This probably signifies that oil is leaking from the bottom of the engine around the piston. This will probably set you back as your engine might need some major engine repairs.

Contact the author: trevorphilips@wheelsjoint.com


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