To start the engine, it is necessary to ignite the mixture in the cylinders. To do this, use a spark plug, between the electrodes of which a spark arises, igniting the mixture in the car engine. The normal start-up and engine performance largely depend on the condition of the candles.
Any spark plug has a steel casing. On its lower part there is a thread for screwing the candle and its side electrode into the chamber part. Inside the candle body, in a sealed insulator there is a metal rod, it serves as a central electrode. On its upper part there is a thread for summing up the tip of the armored wire. The basis of the candle is a ceramic insulator.
For correct and durable operation, the lower part of the insulator with the engine running should reach a temperature of up to 600 0 . Under these conditions, complete combustion of the oil occurs, which gets on the electrodes, and carbon deposits are not formed. At this temperature, self-cleaning candles.
If the temperature is lower, the oil does not completely burn out, and a carbon crust forms on the electrodes, insulator and candle body. The result of this is a failure of its operation, the disappearance of the spark supply (the discharge cannot break through the sediment layer). In such cases, ignition occurs, that is, the fuel mixture is ignited not from an electric spark, but from interaction and direct contact with the red-hot parts of the candle.
Design features of the central electrode and the insulator divide the candles into cold (with the highest heat transfer) and hot (with low heat transfer). The ability to accumulate heat characterizes the glow number of the spark plug. It is indicated on the candle and means the time (in seconds) after which the ignition will occur.
Every car owner caring for his car knows how to check spark plugs for contamination and deposits. With a well-functioning engine, a correctly tuned carburetor / injector and ignition, with the correct operation of the candles themselves, you can see on them deposits of light brown color.
The appearance of a light gray or whitish coating on the insulator cone indicates the presence of problems such as a small octane number of fuel, overheating of spark plugs due to improper installation of the ignition, and poor composition of the working mixture.
Dry black friable carbon deposits indicate over-enrichment of the mixture, late ignition, fairly frequent engine idling. If you adjust the ignition system, soot disappears.
An oily black coating is a sign of a cold candle. A spark does not appear on it, or there is no compression in the cylinder, and it does not give the required power, as a result of which the engine runs unevenly.
The red-brown deposits on the cone of the insulator are the result of fuel combustion, which contains many additives. Such a spark plug must be replaced or mechanically cleaned.
We can safely say that the spark plug is not working if: its thread is in oil, the rim of the body is covered with loose black soot, dark brown spots on the electrodes and insulator, chips and burn-out on the cone of the insulator. Oiled candles in an engine with great mileage indicate wear on pistons, cylinders, rings.
Reduce and eliminate various troubles will help qualified car service every 15-20 thousand km, and timely troubleshooting.