system
Given the following post, respond as if you're commenting on Reddit:
human
eli5 - Why do old cars have more visible smoke coming out of their exhausts?

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