We have a 2007 Chevy Cobalt. I noticed that the tail pipe is black around the

about all the cars you see today have black tailpipes. it,s the kind of gas you have to burn. the next time your in town take a glance at the tailpipes on cars.
 
All exhausts do that to a lesser or greater degree and it depends on the air currents around the rear of the car as to how bad it will be. it should just wash off.
 
the cars fuel injectors are probably running a little rich. That means they are putting slightly too much petrol into the engine.

But this isn't a problem if everything is running smoothly and economically.

You see it isn't necessarily a fault because some engines are designed to run slightly rich... the reasons why are a bit technical, but one simple fact is that a "lean" mixture makes the engine run a bit hot around it's valves and they can burn out, so in order to allow for when you drive up and down mountains, the injectors are set to run slightly rich so the valves are always cool under every driving condition.

Check your fuel consumption. If it's close to that advertised for your model. don't worry about it. If it's using up a bit of gas, mention this exhaust colour when you get the car next serviced
 
It's just from the exhaust coming out, totally normal. If it really bothers you just scrub it off, but it will just come back. It's from the smoke made during the combustion in your engine.
 
All exhausts do that to a lesser or greater degree and it depends on the air currents around the rear of the car as to how bad it will be. it should just wash off.
 
the cars fuel injectors are probably running a little rich. That means they are putting slightly too much petrol into the engine.

But this isn't a problem if everything is running smoothly and economically.

You see it isn't necessarily a fault because some engines are designed to run slightly rich... the reasons why are a bit technical, but one simple fact is that a "lean" mixture makes the engine run a bit hot around it's valves and they can burn out, so in order to allow for when you drive up and down mountains, the injectors are set to run slightly rich so the valves are always cool under every driving condition.

Check your fuel consumption. If it's close to that advertised for your model. don't worry about it. If it's using up a bit of gas, mention this exhaust colour when you get the car next serviced
 
the cars fuel injectors are probably running a little rich. That means they are putting slightly too much petrol into the engine.

But this isn't a problem if everything is running smoothly and economically.

You see it isn't necessarily a fault because some engines are designed to run slightly rich... the reasons why are a bit technical, but one simple fact is that a "lean" mixture makes the engine run a bit hot around it's valves and they can burn out, so in order to allow for when you drive up and down mountains, the injectors are set to run slightly rich so the valves are always cool under every driving condition.

Check your fuel consumption. If it's close to that advertised for your model. don't worry about it. If it's using up a bit of gas, mention this exhaust colour when you get the car next serviced
 
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