The heat rating shows the degree of heat load on the spark plug that the spark plug can withstand. The lower the heat rating of the spark plug, the higher its ability to withstand heat loads. Such a spark plug removes heat better, preventing detonation combustion. A spark plug with a high degree of heat resistance has its drawback, which is that it requires a high self-cleaning temperature. Therefore, such spark plugs become covered with carbon deposits faster, especially in conditions where the engine does not reach its operating temperature during movement (movement in urban conditions, over short distances in winter).
The car manufacturer determines the required glow number of the spark plug and, accordingly, its type. There are spark plugs with one or more electrodes, different lengths and different thread diameters. When replacing spark plugs, it is necessary to follow the instructions of the car manufacturer regarding spark plugs.
The average service life of spark plugs varies and is determined by many factors. The material from which the central electrode is made plays an important role. Chrome-nickel alloy is characterized by high heat resistance and anti-corrosion properties. Silver conducts heat better than all metals, platinum electrodes have the highest resistance to corrosion and carbon deposits. The service life of spark plugs, depending on the material of the electrodes and their number, can range from 30,000 km to 100,000 km of mileage.
You can check the gap between the spark plug electrodes yourself.
1. Unscrew the spark plugs and arrange them in accordance with the order of cylinder firing. Subsequent inspection of the spark plugs will allow you to draw certain conclusions regarding the corresponding cylinder.
2. Do not apply significant force if the spark plugs cannot be unscrewed. The thread of the spark plug hole may be damaged. In this case, warm up the engine and unscrew the spark plugs.
Warning! Do not install cold spark plugs on a hot engine. They will not be able to be unscrewed later, as they will be stuck in place like rivets.
3. If you cannot use a torque wrench when installing spark plugs, follow the following rule to install the spark plugs correctly.
4. Screw in the spark plug until its sealing ring touches the cylinder head surface. Further tightening of the spark plug is impossible without applying a certain amount of force. In this position, tighten the new spark plug by about a quarter of a turn, and the used one by turning the key by about 15°.
Attention! To make the spark plugs easy to unscrew, apply a little graphite to their threads by crumbling a pencil lead, or lubricate them with a thin layer of copper grease. Lubricating the spark plug threads with regular grease or oil only makes things worse. In this case, the spark plugs stick to the thread of the hole.
If the thread in the spark plug hole has been stripped, then workshops in this case use a corresponding threaded sleeve, which is inserted into the spark plug socket.
The condition and appearance of the spark plugs can tell a lot about the engine's operation. If the spark plugs are removed for this purpose, the engine should be warmed up first. Inspect the spark plug, paying special attention to the central electrode insulator and the side electrodes:
- a) the central electrode insulator is grey or brown. The fuel injection system is well adjusted and the engine runs economically;
- b) a layer of deposits. This may be caused by additives in motor oil or fuel, as well as increased oil consumption. You can change the type of oil or fuel;
- c) black soot-like deposits. Due to the vehicle being driven in short-distance mode, the spark plugs do not heat up to the self-cleaning temperature. Incorrect glow number of the spark plug;
- d) white coating on the insulator. The ignition timing is too early. The electronic ignition control or knock sensor is not working;
- d) melting of the central and side electrodes. Overheating of the injectors, faulty electronic ignition control, defective knock sensor or engine overheating due to insufficient cooling;
- e) insulator fracture. At the initial stage, it manifests itself in the form of microscopic cracks. The result of detonation combustion due to refueling with low-quality fuel, incorrect ignition timing, a defective detonation combustion sensor, insufficient cooling or lean mixture due to air "sucking";
- g) oil film on the electrodes and spark plug. Wear of piston rings, valve stems or oil scraper caps.
If the spark plug is outwardly normal, but the engine starts with difficulty, jerkily, then the spark plugs may still be the cause. Cracks in the ceramic insulator that are not visible when inspecting the spark plugs may fill with fuel condensate when starting a cold engine and the spark discharge may be diverted in a different direction. The spark plug may not fire as a result of the pressure that is generated, although it produces a spark when removed.