Correct answer
Yes, it may indicate a combustion problem that should be checked.
Yes. It may indicate poor combustion or excess unburnt fuel, and a professional should identify the cause. Smoke colour is a clue, not an emissions measurement or a sufficient fault diagnosis. Seeing it alone does not establish that the cause is always the same. Drivers must cooperate with legally required emissions or noise tests.
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No, it is always a cooling problem that resolves itself.
Yes, it may indicate a combustion problem that should be checked.
Yes, and black colour alone proves that burning oil is the sole cause.
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