To facilitate starting a cold engine, diesel engines are equipped with a heating system, which consists of glow plugs (one spark plug per cylinder), glow plug control unit, control lamp located in the instrument panel, coolant temperature sensor (only on late models) and associated electrical wires.
Glow plugs are miniature heating elements enclosed in a metal case with a probe at one end and an electrical contact at the other. One candle is screwed into each combustion chamber. When the glow plugs are turned on, they quickly heat up, raising the temperature of the air entering each combustion chamber. The spark plug probe is located directly in the path of the fuel jet from the injectors. Therefore, the fuel passing through the glow plug is also heated, allowing the optimum combustion chamber temperature to be reached more quickly. Additionally, small particles of fuel passing through the glow plugs are ignited and this contributes to the start of the combustion process.
The duration of the heating period is determined by the heating control unit. This device monitors the air temperature in the engine compartment using an ambient air sensor (on earlier models) or coolant temperature (determined by the coolant temperature sensor screwed into the cylinder head - later models). The device changes the heating time period (the time during which the glow plugs are energized), to meet specific conditions.
A warning lamp mounted on the instrument panel informs the driver that heating is in progress. The lamp goes out when the cylinders have warmed up so that the engine can be started. However, supply voltage is applied to the glow plugs until the engine starts. If the engine does not start, power to the glow plugs is cut off so as not to drain the battery and overheat the spark plugs. Note that on later models, the control lamp will light up when the engine is running if there is a problem in the heating system.
Late models have a warm-up mode after starting ("post-heating") - after starting the engine, the glow plugs continue to function. This helps improve fuel combustion until the engine warms up. This mode allows you to make the engine quieter, the ride is smoother, and the emission of harmful components is less. Period duration "post-heating" determined by the coolant temperature.