1. Normal candle
Brown or greyish-yellow color and slight electrode wear. Accurate thermal value for engine and operating conditions.
Helpful advice. When replacing spark plugs with new ones, use spark plugs with the same specifications.
2. Soot deposits
The deposition of dry soot indicates a rich air-fuel mixture or late ignition. Causes misfiring, difficult starting and erratic engine operation. Check if the air filter is clogged, if the coolant temperature and intake air temperature sensors are working.
Helpful advice. use more «hot» candle (elongated insulator with central electrode).
3. Oil deposits
Oily electrodes and spark plug insulator. The reason is oil getting into the combustion chamber. Oil enters the combustion chamber through valve guides or piston rings. Causes difficult starting, misfiring of the cylinder and twitching of the running engine. Required cylinder head repair and piston group of the engine. Replace spark plugs.
4. Overheating
The following reasons are possible: mismatch of the type of spark plug recommended for the engine of your car, early ignition, lean mixture, air leakage into the intake pipe. Check the coolant level and check if the radiator is clogged.
5. Early ignition
Melted electrodes. The insulator is white, but may be dirty due to spark gaps and deposits from the combustion chamber falling on it. May cause engine damage. It is necessary to check the conformity of the type of spark plug, the serviceability of the knock sensor, the cleanliness of the injector nozzles and the fuel filter, the operation of the cooling and lubrication systems.
6. Glaze
The insulator is yellowish, glazed. Indicates that the temperature in the combustion chamber rises unexpectedly during hard acceleration of the vehicle. Normal deposits become conductive. Causes misfires at high speeds.
Helpful advice. After installing new spark plugs, change your driving style. If you do not want to do this, try installing more «cold» candles.
7. Bridge between electrodes
Deposits from the combustion chamber fall between the electrodes. «heavy» deposits collect in the gap between the electrodes and form a bridge. The candle ceases to work, and the cylinder is switched off from work. Identify the faulty spark plug and remove deposits between the electrodes.
8. Ash deposits
Light brown deposits crusting the center and side electrodes. They are isolated from additives to oil or gasoline. A large number of them can lead to insulation of the spark plug electrodes and cause gaps in sparking, interruptions during acceleration. If excessive deposits form in a short time or at low mileage, replace oil seals valve guides to prevent oil from entering the combustion chamber.
Helpful advice. If deposits form consistently over long runs, the reason is the quality of gasoline - change the place of refueling.
9. Wear
Rounded electrodes with a small amount of deposits on the working ends. Normal color. Causes difficult starting in cold or wet weather and reduces fuel economy. Replace the spark plugs with new ones with the same specifications.
10. Detonation
The insulator may be cracked or chipped. This may damage the piston. Make sure the octane rating of the gasoline is correct. Check the knock sensor.
11. Spotted deposits
The soot that has been deposited in the combustion chamber, after proper adjustment, begins to burn out, at high engine speeds it breaks away from the piston and sticks to the candle insulator, causing individual gaps in its operation. Replace spark plugs with new ones or clean old ones.
12. Mechanical damage
Damage can be caused by foreign objects entering the combustion chamber, and if too long a spark plug is used, its electrodes can catch on the piston. This leads to the destruction of the candle, the shutdown of the cylinder and may damage the piston. Remove the foreign object from the cylinder and (or) replace the spark plug.