eli5 – Why do old cars have more visible smoke coming out of their exhausts?

Question

Where is that smoke coming from? Does this means they consume more gasoline?

In: 6

Answer 1

Older engines are less efficient at burning gasoline. The smoke is partially burnt or even unburnt gasoline that is wasted.

Modern engines are better at ensuring a better fuel air ratio with more complete combustion making them more powerful and more efficient.