Combustion

• The combustion of gasoline produces carbon dioxide and water vapor, according to chemistryland.com. Oxygen reacts with hydrogen in gasoline to produce water vapor, which exits the engine through the exhaust manifold.
  
  

Exhaust System

• The exhaust, which includes carbon monoxide, nitrous carbon dioxide, water vapor and unburned gasoline are processed by the catalytic converter, which changes the gasoline to more carbon dioxide and water and directs them into the muffler.
  
  

Other Facts

• In hot weather, the water vapor is less likely to condense and drain, but in cold weather, water vapor will do exactly that and drip from the tailpipe. Over time, water in the exhaust system can cause corrosion.