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supreme_harmony t1_ja4ot1d wrote

Reply to comment by ECatPlay in If the fuel that goes in car engines is extracted from hydrocarbons, which consist of only Hydrogen and Carbon, and those hydrocarbons react with Oxygen in the air (combustion reaction), to produce CO2 and H2O, why do we get a bad smell from car exhaust fumes if both gases are odorless? by Protoflare

This is a fantastic answer. The only thing I would add to the above is that no burn is ever perfect. Exhaust fumes from a car therefore also contain trace amounts of unburnt fuel and even partially burned hydrocarbons of various complexities. These are tiny amounts, but enough for our noses to pick it up.

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Drink15 t1_ja4zrsq wrote

There is also oil that get past the seals and burns with everything else. It’s a small amount in new cars but increases as motor wears

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