Why does the ceramic on the spark plug turn yellow

It is generally suspected to be an air leak.

In the ignition system of a gasoline engine, a high-voltage current is introduced into the cylinder to produce an electric spark to ignite the components of the combustible gas mixture. It is mainly composed of a wiring nut, an insulator, a wiring screw, a central electrode, a side electrode and a shell, and the side electrode is welded to the shell.

The spark plug insulator skirt (the conical part of the insulator outside the central electrode of the spark plug) is in direct contact with the high-temperature gas in the combustion chamber and absorbs a large amount of heat, and the absorbed heat is transferred to the cylinder head and the atmosphere through the housing. Experiments show that in order to ensure the normal operation of the automobile engine, the spark plug insulator skirt should maintain a temperature of 500 600 (this temperature is called the self-cleaning temperature of the spark plug), if the temperature is lower than this value, carbon deposition will be formed in the insulator skirt and cause leakage between the electrodes, affecting the spark plug flashover. If the temperature of the insulation is too high (more than 900 °C), a hot spot fire will occur when the mixture comes into contact with such a hot insulator, resulting in premature ignition of the engine.

The normal operating temperature of the spark plug is between 450 and 870. At this time, the spark plug is yellowish-brown. If the spark plug operating temperature is below 450 for a long time, there will be a lot of carbon deposits around the spark plug, and the spark plug will be black.

It is mainly formed by the dust and oil stains attached to the surface of the ceramic, which are cracked and transformed under high temperature and high pressure.

It is because of the spark plug corona - because the central electrode inside the spark plug conducts high voltage, the high voltage has an adsorption effect on the oil particles floating in the air and adsorbs on the surface of the white insulator.

It's like a plastic bag with static electricity that will suck on people, the high-voltage parts of an old-fashioned TV will absorb dust, and a high-voltage electric box will suck people.

In addition, due to the blocking effect of the rubber sleeve of the ignition coil (cylinder wire), the corona is only available in the section close to the metal housing.

Corona does not affect the performance of the spark plug and is not directly related to the service life of the spark plug. Corona is not used as a basis for judging whether the spark plug is to be replaced.

The reason for the yellowing of the ceramic of the spark plug is: the spark plug is not tightened, the air leaks, and the situation is caused by high temperature. A spark plug can be replaced in time to solve the problem.

The metal housing of the spark plug (except for the electrodes and gasket parts) is mainly made of steel, and a thin anti-corrosion coating is plated on the outside. When the steel is heated, an extremely thin oxide film (below 500) is produced due to the interaction between the steel and the oxygen in the air, and the color of the oxide film changes with the change of temperature.

The temperature of the steel will also change when the temperature is higher. This gives a rough estimate of the approximate temperature of each part of the spark plug. The color of the spark plug housing is the evidence that reflects whether the spark plug is leaking and overheating, and of course, the influence and change of gasoline composition, gasoline additive composition, and engine oil composition on the color of the spark plug housing should be ruled out.

Oily sediments. There are oily deposits on the spark plugs, indicating that the lubricating oil has entered the combustion chamber. If it's just an individual spark plug, it may be a damaged valve stem oil seal.

If this deposit is stuck to the spark plugs of each cylinder, indicating oil channeling in the cylinder, the air cleaner and ventilation should be checked for blockage. Remove the spark plug and observe, if it is russet or rust colored, it indicates that the spark plug is normal; If it is oily, it indicates that the spark plug gap is out of balance or too much oil, and the high-voltage line is short-circuited or open-circuited; If it is smoky black, it means that the spark plug is selected incorrectly or the mixture is thick, and the oil is channeled; If there is a deposit between the top and the electrode, when it is an oily deposit, it means that the cylinder channeling oil has nothing to do with the spark plug, when it is a black deposit, it means that the spark plug is deposed with carbon and bypassed, and when it is a gray deposit, it is the additives in the gasoline that cover the electrode and cause a lack of fire; Severe ablation, such as scarring at the tip, cracking of black patterns, or melting of electrodes, indicates damage to the spark plug.

The biggest role of spark plug ceramics is insulation, when some car owners will find that the ceramic of the spark plug is yellow, can the spark plug ceramic part be yellow?

In fact, it is normal for the spark plug ceramic to turn yellow, and the main reason for the yellowing is that the skirt of the spark plug insulator will be in direct contact with the high-temperature gas in the combustion chamber, and will also absorb a large amount of heat, when the inhaled heat is transmitted to the cylinder head through the shell. In order to ensure the normal operation of the engine, the insulator skirt should be kept at a temperature of 500 600 °C, if the temperature is low, the skirt will form carbon deposits, causing leakage between the electrodes, affecting the spark plug flashover, resulting in the yellowing of the spark plug ceramic.

If the spark plug ceramic is broken, it must be replaced in time. The impact of the fracture is insufficient ignition, engine shaking, lack of power, and in severe cases, engine breakdown.

If there is a yellowing situation, you can not replace it first, continue to observe the suspicion, and replace it as soon as possible if there is a break.

Abstract The yellowing of ceramics is mainly due to the leakage breakdown of the spark plug itself, and the other is that the temperature of the electric spark itself is relatively high, so that the temperature of the spark itself is too high.

Why does the ceramic of the spark plug turn yellow, and what is going on?

The yellowing of ceramics is mainly due to the leakage breakdown of the spark plug itself, and the other is that the temperature of the spark itself is relatively high, so that the temperature of the spark itself is too high.

If this is the case or if the spark plug is removed, then the spark plug needs to be replaced.

Because from this yellowing, it is generally possible that the spark plug itself has the problem of leakage.

<> "Exposing pseudo-common sense, spark plug ceramics turning yellow is air leakage?

In the daily maintenance of the car, replacing the spark plug is a relatively common one, when the vehicle travels more kilometers, there will be a weakening of power and an increase in fuel consumption, at this time it is necessary to consider whether to replace the spark plug. But the reason why many car owners replace spark plugs is probably because the maintenance worker said: your spark plug ceramic body has turned yellow, and there are traces of air leakage in Mingmin Xinliang, which needs to be replaced.

Is that really the case?

The yellowing of the spark plug ceramics indicates that the spark plug is leaking, which has become a classic rumor in the auto repair industry, and it is estimated that even they themselves can't tell whether it is a rumor or the truth. The National Standard of the People's Republic of China GB 7825-1987 stipulates the hot sealing performance of the wide spark plug of the fire bridge: when the temperature of the air medium around the spark plug electrode is 190-220 and the air pressure difference is 190-220.

And after holding for 4-5min, the total air leakage of each part of the spark plug should not exceed 5ml min. That is to say, when the spark plug is working, it cannot exceed 5 ml of air leakage per minute, and it is considered to be qualified. Whether the spark plug itself is leaking or not cannot be known without scientific testing by professional equipment.

Generally speaking, all spark plugs of regular manufacturers are qualified, and we can roughly think that there is no air leakage with a very small and very small air leakage. So what's going on with yellowing?

This yellow, brown dirt is called corona. Because the central electrode conducts high-voltage electricity when the spark plug is working, the high-voltage electricity will adsorb the free gasoline particles floating around the spark plug ceramic body on the ceramic surface. Since the upper ignition coil is protected by a rubber sleeve, there will only be an adsorbed corona near the electrode.

Corona does not affect the performance of the spark plug, and there is no direct relationship with the service life of the spark plug, so it cannot be used as a basis for judging whether the spark plug should be replaced.

That is to say, if the car has never replaced the spark plug, but there are signs of yellowing around the ceramic body, it is likely to be a normal phenomenon after a period of daily use, and there is no need to replace it. However, if the spark plug has obvious electrode damage, breakage, and electrode melting, it must be replaced in time.

So where did this leaky rumor come from? What is the real sense of air leakage? It turns out that if the spark plug is not locked according to the torque required by the manufacturer when the spark plug is installed, there will be a gap in the spark plug sealing gasket, which is the culprit of air leakage.

It is necessary to replace the spark plug according to the use of your vehicle, but we also need to know some basic common sense to help you better judge and reduce being "fooled".

Spark plugs will also encounter a variety of problems when they are used, and they need to be well maintained, so what are the reasons for spark plug ceramic cracking?

1. The voltage is unstable. The reason for the cracking of spark plug ceramics has a lot to do with the voltage is not silver, which is also the most common, because when the insulation ability of the high-voltage ignition coil decreases, the additional resistance is damaged or the working capacity is reduced, and so on, and the voltage reduction will cause the spark plug to deposition and burn, so that the ceramics will crack. This reason needs to be corrected after passing the inspection, and the problem of voltage instability should be corrected.

2. High temperature. The cracking of spark plug ceramics also has a lot to do with high temperatures, such as ignition in advance, but the cooling system is faulty, there are problems such as insufficient lubrication, excessive valve clearance, etc., which will make the cylinder temperature rise, and the ceramics will crack because of the breakdown. For this situation, it is necessary to replenish the engine oil at the time of Changchong to ensure that the cooling system is normal.

3. The quality of the spark plug is poor. If the quality of the spark plug you buy is particularly poor, it is also easy to cause poor heat dissipation and explode the ceramic, so you must choose the best spark plug.