Thermal characteristic (glow number) spark plug is an indicator of the degree of heat load of the spark plug in the engine under certain operating conditions. The lower the glow number of the candle, the higher its ability to withstand heat stress. Candle can better dissipate heat, thereby preventing damage due to pre-ignition (engine knock). A spark plug with a high heat load capacity has the disadvantage that its self-cleaning temperature is correspondingly higher. Such a plug is more prone to smoke, especially if the engine often does not reach its operating temperature during operation (urban cycle, driving in short stretches in winter). Usually, "cold" candles (with heat numbers starting from 06) installed on "hot" engines, i.e., for power units that require more power.
The heat number is contained in the designation of the candle. The designation of the candle is deciphered as follows:
Bosch spark plugs
Example:
W R 7 D C
1 2 3 4 5
1 - W = thread M 14x1.25 with flat sealing surface, SW 21;
F = thread M 14x1.25 with flat sealing surface, SW 16;
M = thread M 18x1.5 with flat sealing surface, SW 25;
H = thread M 14x1.25 with conical sealing surface, SW 16;
D = thread M 18x1.5 with conical sealing surface, SW 21;
SW = key size.
2 - R = with radio interference suppression resistor. Does not affect the operation of the ignition system.
3 - Heat number. Scale of incandescent numbers from 06 "cold" up to 13 "warm". In this case, the value of the glow number 7 corresponds to the value of 175 on the old scale, 6 - 200; 5 - 225, etc.
4 - A = thread length 12.7 mm, normal spark;
B = thread length 12.7 mm, extended spark;
C = thread length 19 mm, normal spark;
D = thread length 19 mm, extended spark.
5 - material of the central electrode: No designation = alloy of chromium and nickel;
C = nickel and copper compound,
S = silver,
P = platinum,
O = standard spark plug with reinforced center electrode.
Due to the copper core in the central electrode, and even more due to the silver central electrode, the thermal conductivity is significantly increased.
BERU candles
Example:
14 R 7 D U
1 2 3 4 5
1 - thread diameter in mm, here M14 x 1.25
2 - design feature, for example, K for a flat sealing surface, K for a radio interference suppression resistor
3 - glow number (like Bosch)
4 - thread length (like Bosch)
5 - electrode material, for example U for a copper core
As standard, MAZDA models are in most cases equipped with NGK or Nippondenso spark plugs. Standards vary from manufacturer to manufacturer. When replacing, you can install candles BOSH and BERU.