What spark plugs color and deposits tell about an engine

COPYRIGHT WARNING:
All pictures and texts in this web page are the property of nomaallim.com. Any use of any part of those contents without the written consent of nomaallim.com shall be subject to legal procedures as per international and local laws in the concerned country. Using the name "nomaallim" or "nomaallim com" or "nomaallim.com" in the text describing the unauthorized copied content shall not constitute an exception and shall be sanctioned in accordance to the effective laws and proceedings.

DISCLAIMER:
Our pictorials are of informative nature and do illustrate works carried out by ourselves at our own premises for our own use and satisfaction.
Readers who envisage to carry out similar works inspired by the below method shall do this at their own risks and liability.

Context of the below spark plugs symptoms

The below described spark plugs observations occurred on modern MPFI engines with or without direct injection.
They do appear when the engine starts to age while all is still normal i.e. you almost feel no failure and the MIL light (check-engine light) remains off. The only symptoms you will notice are a substantial increase of fuel and oil consumption.
Although they remain valid for older carburetor fitted engines, they do not constitute the most common failure on these, since carburetors require frequent adjustments; black carbonized plugs denoting a rich mixture are the most common condition found on such engines along with misfiring caused by the older generation of spark plugs and distributor ignition systems.

Spark Plugs diagnostic No 1: Oily and wet black appearance of the spark plugs electrodes | Excessive oil consumption.

The spark plugs are covered with a black and wet coating especially the central electrode.
This denotes an excessive engine oil consumption; which could indicate worn spark plugs seats.
Check our specific oil consumption diagnostic schedule for more details.

Spark Plugs diagnostic No 2: White and thick deposits on electrodes | Fuel additives

The below shown white thick deposits are typical to the use of fuel additives on a high oil consumption engine. When you use injection cleaners on an aged engine, you might notice a cloud of smoke left behind your car under some driving conditions and these associated deposits on the spark plugs. Check and fix your excessive oil consumption, avoid using fuel additives on aged engines.

Spark Plugs diagnostic No 3: Engine pressure wash

The use of a water pressure jet machine to clean the engine is allowed as long as the operator knows where to direct the jet. In most cases, the powerful water jet can hit unwanted places of the engine like the COP's and could result in little water infiltration in the spark plugs wells which will turn into trapped moisture and corrode both the spark plug insulator and nut.
Make sure to remove the COP's after an engine wash and treat them as described in our specific tutorial.
Removing the COP's while the engine is hot will also guarantee that the moisture in the spark plugs wells will evaporate.

Spark Plugs diagnostic No 4: burnt spark plug insulator

The below pictures show how the insulator suffers extreme heat at the contact with the metal part of the plug.
To the left, a spark plug that was driven for 13,000 Km, to the right 30,000 Km.
One can see how the burns progress.
It is also possible that the inner seal broke letting some combustion gas out.

The only possible preventive remedy when refitting new plugs is to make sure the plug is tightened to 2.5 mKg to ensure optimum heat conductivity with the cylinder head.

13,000 Km iridium spark plug

30,000 Km iridium spark plug

Spark Plugs diagnostic No 5: damaged earth electrode

The platinum center electrode suffers almost no damage compared to the earth electrode which is seen here with a hole at the Km 13,000 only.
The hole increases the gap between electrodes and weakens the spark due to the deterioration of the material inside the worn circle. This is a spark plug fault, however it can be increased by super knock.