How to read your Spark Plugs?

Oh no, you have a check engine light on your dashboard. How can you determine what is wrong with your engine? The spark plugs in your engine can tell you a lot about how your engine is performing, if you suspect there is something wrong with your vehicle; checking your spark plugs isn't a bad idea. This applies to your car, ATV, boat, motorcycle, moped and even your lawn equipment. Using this article you can find engine problems yourself.

Before you take out your sparkplugs, make sure the engine is turned off, the key is out of the ignition and that the engine and its surroundings had enough time to cool.

Colour is a great indicator to determine your air to fuel mixture, if you own a twostroke vehicle; you might benefit from checking our SparkPlug colour Chart .
we are currently still building this colour chart. Do you want to contribute? Please email us our pictures of your sparkplugs. We will provide immideate support to help you!

Genrally speaking, a lightly brown coloured spark plug (often described as coffee coloured) is the best colour the electrodes can have. This means that the mixture of air to fuel is perfectly in line with the temperature the spark plug is operating at. This means that the engine is in a good condition and should be functioning properly.

A dark colour of the firing nose, very black and dry or extremely wet and black, usually indicate that the air to fuel mixture is too rich in fuel, the temperature rating of the spark is too cold, there is a vacuum leak, extremely late/soon ignition timing or low compression.

A very wet condition (usually black coloured too) can indicate a blown head gasket, a faulty mixture of air to fuel or a wrongly set injector/carburettor.

Refrences in the following piece of text refer to the picture above. The spark plugs are counted from left to right, starting at one.

Normal state
If the firing end of your spark plug resembles spark plug 2, that means that it s performing optimally. When resolving engine problems you should aim to have a spark plug which looks like this.
Lean state
When your engine is running on a mixture which is too lean in fuel, the spark plug will resemble number 3 and 4 the most. This can be fixed by increasing the amount of fuel in the mixture.
Wet/dry state
There are many different causes for this state. Watch out that the resistance between the center electrode and the housing does not drop to 0 ohms. If that happens the spark plug is not able to fire anymore. Sometimes you can fix a wet spark plug by cleaning the spark plugs. A great example is spark plug 3.
If your spark plug is overheating you will see a shimmer on the firing tip. It looks like the sparkplug has momentarily melted and is a bit more glossy than usual.
Unidentifiable deposits
If you find lots of unidentifiable deposits all over your spark plug, you might have a leak into your cylinder. These deposits come from oil, bad fuel and dirty air; and can severely damage your engine.