Spark plugs — general information (VW Transporter T4)

The spark plug consists of an insulator, a housing, a central electrode, and a ground electrode. The ground electrode is tightly fixed in the insulator. The insulator is rigidly connected to the housing. An ignition spark jumps between the central and ground electrodes, igniting the air-fuel mixture.

The spark plug determines the ease of starting, idle characteristics, acceleration and maximum speed. Therefore, it is impossible to deviate from the type of spark plugs prescribed by the manufacturer without reason, which is determined by the heat rating. The heat rating indicates the degree of heat load of the spark plug in the engine under certain operating conditions.

Engine spark plugs are selected so that they reach the self-cleaning temperature under various operating conditions. The lower the glow number of the spark plug, the higher its glow ignition resistance and the lower its resistance to contamination. The higher the glow number of the spark plug, the lower its glow ignition resistance and the higher its resistance to contamination.

The glow plug heat rating is contained in the spark plug code. The code is deciphered as shown below.

Spark plug BOSH

F	R	G	D	U	R
1	2	3	4	5	6

The text is copied from this portal: VWmanual

1.

• W – thread M14 x 1.25 with flat seat, SW21;
• F-thread M14x1. 25 with a flat fit, SW16;
• M – thread 18 x 1.5 with flat seat, SW25;
• H – thread M14 x 1.25 with conical fit, SW16;
• D – thread M18 x 1.25 with conical fit, SW 21;
• SW – key size.

2. R – with a noise suppression resistor. The operation of the ignition system is not disrupted.



3. Heat rating. The heat rating scale has designations from 06 ("cold") to 13 ("hot"). The number 7 corresponds to the old heat rating of 175 (old designation), 6-200, 5-225, etc.

4.

• A – thread length 12.7 mm, normal spark discharge trajectory;
• 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;
• DT – thread length 19mm, elongated spark discharge path, 3 ground electrode;
• L – thread length 19 mm, highly elongated spark discharge trajectory.

5. Electrode material of the central electrode: Cr-Ni alloy;

• C – central electrode made of Ni-Cr compound;
• S – silver central electrode;
• P – platinum central electrode;
• O – standard spark plug with reinforced central electrode.

6. R = 1 kOhm, resistance to burning, X – distance between electrodes 1.1 mm.

Due to the inclusion of copper (Cu) in the central electrode and, even more, when using a silver electrode, the thermal conductivity and, therefore, the thermal load are increased. The advantage of a spark plug with a platinum central electrode is a high sparking ability, low wear and a wide glow range.

Spark plug BERU

14	F	G	D	U	R
1	2	3	4	5	6

1. Thread diameter in mm, here M14 x 1.25.

2. Design, for example K – for conical fit, F – for flat fit, SW16, R with interference suppression register.

3. Heat rating. The heat rating scale has designations from 06 ("cold") to 13 ("hot"). The number 7 corresponds to the old heat rating of 175 (old designation), 6-200, 5-225, etc.


4.

• A – thread length 12.7 mm, normal spark discharge trajectory;
• 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;
• OT – thread length 19mm, elongated spark discharge trajectory, 3 ground electrode;
• L – thread length 19 mm, highly elongated spark discharge trajectory.

5. Electrode material, for example, with U copper inclusions.

6. R = 1 kOhm, resistance to burning.