The heat number is contained in the designation of the candle. The designation is deciphered as follows:
Bosch spark plugs
Example: WR 7 D C R
- 1) W = M14S1.25 thread with flat sealing surface. wrench size 21 mm: F - thread M14S1.25 with flat sealing surface, wrench size 16 mm; M - thread M18S1.5 with a flat sealing surface, key size 25 mm; H - thread M14S1.25 with a conical sealing surface, key size 16 mm; D - thread M18Sl.5 with conical sealing surface, wrench size 21 mm.
- 2) R - with resistance to radio interference, does not affect the functioning of the ignition system.
- 3) 7 - glow number. The heat number scale has a range of 06 («cold») — 13 («hot»). In this case, the number 7 corresponds to the previous designation 175.6 - 200.5-225, etc.
- 4) A - thread length 12.7 mm, normal spark position; B - thread length 12.7 mm, extended spark position; C - thread length 19 mm, normal spark position; D - thread length 19 mm, extended spark position; DT - thread length 19 mm, extended spark position, 3 ground electrodes; L - thread length 19 mm, significantly extended spark position;
- 5) center electrode material: Cr-Ni alloy (Cr-Ni = chromium-nickel). C - Ni-Cu-alloy (Ni-Cu - nickel-copper), S — silver central electrode, P — platinum central electrode. 0 - standard spark plug with reinforced center electrode.
- 6) R - 1 com. extinguishing resistance. 1 kOhm
Thanks to copper (Cu), and even more so for the silver central electrode, the thermal conductivity increases, and hence the heat resistance. The advantages of plugs with platinum center electrodes are easier sparking, as well as less wear and a wide temperature range.
Beru spark plugs
Example: 14 K 7 DUR
- 1) Thread diameter, here M14S1.25.
- 2) A design feature, for example, k is a conical sealing surface, R is the presence of radio interference resistance 5/10 kOhm.
- 3) Heat number - the decoding is the same as for Bosch candles, except for Silverstone candles: here the designation S6 corresponds to the heat number 145-200, S7 - 200-215.
- 4) Thread length - the decoding is the same as for Bosch candles. Except for Silverstone candles: here the designation S6 is a short thread, S7 is a long thread.
- 5) Central electrode material: U - Ni-Cu-alloy. A candle with a silver center electrode is indicated «Silverstone». Spark plug «Silverstone» have a service life determined by Vega, 50,000 km.
- 6) R is the damping resistance. 1 kOhm
The value of the glow number recommended by the manufacturer can only be deviated from if the operating conditions differ significantly from normal and malfunctions occur. If the candles are constantly covered with soot, that is, they do not reach the self-cleaning temperature (when traveling short distances), then it is recommended to replace them with candles with the next, higher value of the glow number. If the engine is operated exclusively at full load, it is recommended to replace the spark plugs with spark plugs with the next lower glow number.
Spark plug torque: 25 Nm.
Recommended spark plugs for BMW vehicles
Attention: To take into account the constant technical progress - it is likely that other types of spark plugs can be installed on older cars. Therefore, it is recommended to obtain information about the admissibility of installing one or another type of candles at the service station.