Would that be a burned glow?
I have massive problems with NGK that will not stand the heat on a E300 turbo.
They lastet more or less 6 month.

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E300TD year 2000. RUSTY SOLD
cost a fortune to maintain on the road
but run well on WVO
Second Merc died due to corrosion ( NOT rust) How can mercedes get away with that for so long?
Third lasted a month then went away...
Fourth now... Corroded too...