The heat number indicates the degree of permissible heat load of the spark plug. The lower the glow number of a spark plug, the higher its thermal load capacity. The candle at the same time conducts heat better, thereby preventing glow ignition (knocking noises when engine is running). A spark plug with a high thermal load capacity has, above all, the disadvantage that its self-cleaning temperature is correspondingly higher. Therefore, carbon deposits form on it faster, especially when the engine often does not reach its operating temperature when traveling (city driving, short distances in winter). Usually, «cold» candles (glow number from 06) installed on «hot engines», from which a large power is required as part of the power plant.
In the presence of copper (Cu) and to an even greater extent of the silver center electrode, the thermal conductivity and with it the permissible thermal load of the candle increase. The heat number is contained in the designation of the candle. This designation includes the following:
1)
W - thread M14x1.25 with flat seal, SW 21;
F - thread M14x1.25 with flat seal, SW 16;
M - thread M18x1.5 with a flat seal, SW25;
H - thread M14x1.25 with conical seal, SW 16;
D - M18x1.5 thread with conical seal, SW21; (SW - turnkey size).
2) Heat number. The thermal scale value is indicated from 06 («cold») up to 13 («warm»). In this case, the number 7 corresponds to a thermal value of 175 (former designation), 6 - 200.5-225, etc.
3)
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 trajectory of the spark discharge;
D - thread length 19 mm, elongated spark discharge trajectory;
L - thread length 19 mm, far elongated spark discharge trajectory.
4) Execution of electrodes: T — 3 electrodes of mass;
5) Material of the central electrode: no designation - Cr-Ni - alloy; C - Ni-Cu - alloy; S - silver; P - platinum; O - a standard candle with a reinforced central electrode, For Beru candles: U - copper.
Standard spark plugs for Passat car engines
1) For all engines, only a part of the approved spark plugs is shown.
2) Replace spark plugs after 60,000 km.
3) Distance between electrodes: 0.9-1.1 mm.
4) When replacing spark plugs, use only the same spark plugs.
5) Distance between workpiece electrode and insulator: max. 0.8 mm.
6) Distance between workpiece electrode and insulator: max. 0.6 mm.
7) When running on Super-Plus gasoline.
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