Reading spark plugs

3 posts in this topic

I have pulled my plugs some time ago and have these pictures below.

Basically, upper spark plugs have some white deposits, and lower exhaust ones have black carbon deposits.


No issue, I just want to understand better. Slightly higher fuel consumption than advertised: 55 mpg at steady 60 mph, and 35 mpg in short-distance (5mi) city driving.

Car: Roadster 452.


Is it normal for plugs to be different in same cylinder? All three cylinders look consistent.

Is the lower plug working too cold? Perhaps I could upgrade these lower plugs to hotter model?





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Lower plugs always turn black and sooty. I simply give them a good clean with a brass wire brush and swap upper and lower plugs when refitting. 

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