Looking through the tails of some exhaust pipes, you will see how clean and neat they are. If your food mistakenly falls into it you may not have any problem picking it up and eating but examining some others, you see them full of charcoal-like substance, very dark?

I find it difficult to believe this reflects the state of the engine because funny enough, I see some old or tokunbo cars with clean exhaust but some new cars with soot covered exhaust.

Does the quality of fuel or the car fuel system contribute to this or what could be responsible for this?

Civil and enlightening comments will be appreciated.

Cartalk is the appropriate section for this type of topic.
Quality of fuel combustion affects the state of the exhaust pipe. Gunky exhausts are usually caused by bad fuel, oil leak into combustion chamber and bad air/fuel ratio.

OK, tanx.