Spark plugs (BMW 5 Series E39)

The spark plug consists of an insulator, a housing, a central electrode and a ground electrode. The central electrode is hermetically secured in the insulator, and the insulator is firmly connected to the housing. An electric spark jumps between the electrodes, which should ignite the fuel-air mixture. The starting qualities of the engine, idle properties, acceleration and maximum speed of the car depend on the spark plug. Therefore, it is impossible to deviate from the spark plug type prescribed by the manufacturer, which is determined by the heat rating, without good reason. The heat rating indicates the degree of permissible thermal load of the spark plug under certain operating conditions. Spark plugs for engines are selected so that they reach the self-cleaning temperature, if possible, under all road conditions. The lower the heat rating of the spark plug, the higher its resistance to glow ignition and the lower its resistance to contamination. The higher the heat rating of the spark plug, the lower its resistance to glow ignition and the higher its resistance to contamination.

The heat rating is contained in the spark plug designation. This designation includes the following:

Example: Bosch spark plugs



1 - thread

• W - thread M14 x 1.25 with flat seal, SW 21; (SW - turnkey size)
• F - thread M14 x 1.25 with flat seal, SW 16;
• M - thread M16 x 1.5 with flat seal, SW 25;
• H - thread M14 x 1.25 with conical seal, SW 16;

2 - Heat rating. The heat scale value is indicated from 06 ("cold") to 13 ("warm"). The number 8 corresponds to a heat rating of 150 (former designation), 7 - 175, 6 - 200, etc.

3 - thread length.

• B - thread length 12.7 mm, elongated spark discharge trajectory;
• C - thread length 19 mm, normal spark discharge trajectory;
• D - thread length 19 mm, elongated spark discharge trajectory;
• L - thread length 19 mm, long spark discharge path. Thread length data applies to spark plugs with flat seals. Additional symbol T (for example, DT) indicates the presence of three mass electrodes.

4 - Design of electrodes.

5 - Central electrode material:

• in the absence of the symbol - Cr-Ni - alloy;
• C - Ni-Cu - alloy;
• S - silver;
• P - platinum.

6, R - with resistance for protection against interference. Due to this, the operation of the ignition system is not disrupted.