for every 100 gallons of gasoline, you produce 90-120 gallons of water, 3-10 gallons of unburned gasoline, .5 to 3-lbs. of soot and carbon, 0.25-1-lb. of varnish, and 1-4-lbs. of sulfuric and nitric acid. Most of it goes out the tailpipe, but some of it flows into the crankcase. Water, soot, carbon, and acids all deplete motor oil additives.

Engines always run rich at cold startup. They have to to overcome the quenching effect of cold metal. Once the engine reaches operating temperature, the computer cuts back on the fuel

to add, support,

2005 be an OBDII platform. as such it likely has a full compliment of exhaust o2 sensors. iffin she was running rich, the computer would see that condition via those sensors and prompt a CEL/MIL light.

There is always black stuff in a car exhaust, it is a byproduct of combustion.

Black soot in the exhaust has become normal and harmless for many vehicles.No one seems to agree why this is happening.

It's a 2005 sunfire 2.2L engine. It's been sitting for 2 months and we started it up and put my hand in the exhaust, there was black stuff in there (soot?). What could this be? It can't be driven right now because it isn't insured or registered, mechanic told me on the phone though if u turn a car on that's been sittings or a while but don't actually take it for a drive that can result in black residue. Is that true what could it be and is it expensive to fix