Pre-heating system — description and testing (Audi 100 C3)

To facilitate cold starting, diesel models are equipped with a pre-heating system consisting of four glow plugs, a control unit, and a control lamp installed in the instrument panel.

Glow plugs are miniature heating elements in a metal housing that are connected to the electrical network. Each glow plug is screwed into the cylinder head, and the tip of the plug is placed in a swirl chamber. When the plug glows, the air in the cylinder heats up, thereby reaching combustion temperature faster.

The duration of the warm-up period is controlled by a system that receives engine temperature information from the coolant temperature sensor and adjusts the warm-up time based on this information.

A control lamp installed in the instrument panel informs the driver that the heating is on. The lamp goes out after the temperature in the vortex chamber reaches a level sufficient to start the engine. When the engine is warmed up or the ambient temperature is more than 8°C, the lamp will only light for about one second, after which the engine can be started.