The glow number determines the degree of heat resistance of the candle. The lower the glow number of the candle, the higher its heat resistance. This means that the spark plug is better at dissipating heat, reducing the likelihood of glow ignition (detonation). A disadvantage of a high heat resistance plug is its higher self-cleaning temperature. This leads to more intense carbon formation, especially when the engine does not reach its operating temperature during operation (urban driving, short distances in winter). Usually, "cold" candles (heat number starting from 06) installed on "hot" engines, i.e. for engines that require high power output.
The heat number is indicated in the marking of the candle. The marking of the candle has the following structure:
Bosch candles
Marking example:
W | R | 7 | D | WITH |
1 | 2 | 3 | 4 | 5 |
(1) W=M14x1.25 thread with flat sealing surface, wrench size 21; F=M14x1.25 thread with flat sealing face, SW 16; M = thread M18x 1.5 with a flat sealing surface, turnkey size 25; H=M14x1.25 thread with conical sealing surface, turnkey size 16; D=thread M18x1.5 with conical sealing surface, wrench size 21.
(2) R = with an interference suppression resistor, this indicator does not affect the performance of the candle.
(3) Heat number. The heat number is in the range from 06 ("cold") to 10 ("hot"). In this case, the number 7 corresponds to the old designation of the glow number 17 corresponds to 200.5-225, etc.
(4) A = thread length 12.7 mm, no protrusion
B = thread length 12.7 mm, raised
C=thread length 19 mm, no protrusion
D=19mm thread length with thermal case protrusion
(5) center electrode material: n/a = chromium-nickel alloy; C = electrode material is composite, consists of nickel and copper; S = silver center electrode; P = platinum; O = standard plug with reinforced, center electrode.
Thanks to the copper core (Cu) on the central electrode, and even more thanks to the central electrode made of silver, it increases the thermal conductivity of the candle and its heat resistance.
Beru candles
Designation example:
14 | R | 7 | D | U |
1 | 2 | 3 | 4 | 5 |
(1) thread diameter in mm, here M14x1.25.
(2) constructive sign, for example,? means cone interface, R - the presence of an interference suppression resistor.
(3) glow number (like Bosch).
(4) thread length (like Bosch)
(5) electrode material, for example, U - with a copper core.
Serial models of TOYOTA COROLLA cars are in most cases equipped with NGK or Nippondenso spark plugs. Different manufacturers use different candles. When replacing standard spark plugs, you can use Bosch and Beru spark plugs.