spark plug temp grade

Matt82

Matt82

Matt82

Soldato
Joined
13 Mar 2004
Posts
16,649
ive got a feeling i may have the wrong temp grade spark plugs in my car

i had one of them out the other day and the electrode was pretty sooty. with previous plugs they would always come out that perfect coffee colour.

the car should have NGK BKUR6ET-10

gsf didnt have these, i fancied a change too, so took some bosch platinums in there

BOSCH F5DP0R (Platinum)

can anyone remember if thats a grade hotter or colder or equivalent?
 
For NGK's the heat rating is the number in the middle, in this case it's 6. The higher the number the cooler the plug, which means the electrode is less exposed because it's more shielded from the engine heat. One step hotter or colder is unlikely to cause the plug to soot up in my experience.

I reckon the Bosch heat rating is the 5 in the model number, so that would be one stage hotter.

It's usually best to stick with what the manufacturer recommends otherwise economy can suffer, the engine can be difficult to start in the cold (too cool a plug), the plugs can foul up (too cool), or the engine can detonate (too hot). Only change the heat ratings if you've modified the engine.
 
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bosch 5 grade are colder than ngk 6 grade

as i thought, ive got a colder plug than needed, hence theyre staying sooty
 
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