Exhaust tips naturally turn black over time due to incomplete combustion. It's an inevitable part of any combustion engine. The gasoline rarely gets 100% burned up, and the remaining hydrocarbons are sent out the exhaust tips as soot. This carbon buildup is black-colored and sticks to the exhaust as you drive. Learning how to clean exhaust tips is easy, though, and can get your tailpipes shining like new again.