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White smoke from the tailpipe is usually attributable to an engine combusting either antifreeze or water. Black smoke is caused by burning too much fuel and blue smoke is caused by burning oil...So I would say that your BMW is burning coolant of some kind. Does it smoke all the time the engine is running or just when it is cold?
Black smoke is usually excess fuel, that can be caused by things such as leaky fuel injectors, bad coolant temp sensor, weak spark (bad coil?). You don't say what year or engine. If a carburetor, it may need overhaul. If excess fuel gets really bad, it can wash the oil off the piston rings and cause rings to wear, plus dilute engine oil causing bearing failure.
Did you talk to the service people about the problem? I would take it back if they included a charge for looking into the problem. If it was a dealer I would definately return it and talk to the service manager. Otherwise, you may want to take it buy your favorite auto parts store and ask them to read the ECU (fuel brain) for error codes.
White smoke is caused by raw, un-burnt fuel passing into the exhaust stream. Common causes include:
·Incorrect fuel injection timing
·Defective fuel injectors
·Low cylinder compression
Low cylinder compression may be caused by leaking valves, sticking piston rings, ring wear, cylinder wear, or cylinder glaze. When white smoke occurs at cold start and then disappears as the engine warms up, the most common causes are fouling deposits around piston rings and/or cylinder glazing.
Continuous evidence of white smoke indicates a mechanical defect, or incorrect fuel timing.
Yes this is correct, you can get important information from the colour of smoke from the exhaust:
Blue/Gray Smoke: Blue/gray exhaust smoke is an indication of oil burning in the combustion chamber. These are possible symptoms and causes:
Valve Seals: Leaking valve seals will cause blue/gray smoke at startup because oil leaks past the seals into the cylinder after the engine shuts down.
Valve Guides: Excessive clearance between the valve stem and the valve guide allows oil to leak past the gap into the cylinder.
Piston Rings: Worn or damaged piston rings will cause blow-by resulting in blue/gray smoke.
Worn Cylinder Walls: Worn cylinder walls cause blow-by resulting in blue/gray smoke.
PCV System: A stuck closed PCV valve will cause excessive crankcase pressure resulting in blue/gray smoke.
Black Smoke: Black exhaust smoke is an indication of a rich fuel condition. These are possible causes:
Fuel Injectors: A leaking or dripping fuel injector will cause a rich fuel condition.
Fuel Pressure Regulator: A stuck closed fuel pressure regulator will cause a rich fuel condition.
Fuel Return: A restricted fuel return line will cause a rich fuel condition.
White/Gray Smoke: White exhaust smoke is an indication that coolant is burning in the combustion chamber. These are possible causes:
Cylinder Head: A crack in the cylinder head (around the coolant jacket) will cause coolant to enter the combustion chamber.
Engine Block: A crack in the deck of an engine block near the coolant jacket will cause coolant to enter the combustion chamber.
Head Gasket: A damaged or blown head gasket will cause coolant to enter the combustion chamber resulting in white/gray smoke coming from the tailpipe.
There are a number of possible reasons to get smoke including:
Cylinder bore scored, causing rings to not seat.
Damaged rings during piston replacement
Valve guides leaking
Mixture wrong (is smoke blue, white or black?)
Blue smoke is caused by oil. Rich running causes black smoke and will set the check engine light. Rich running (black smoke) on startup could be caused by a leaking injector. The blue smoke puff at startup is likely valve stem seals leaking or a bad crank case vent malfunction and sucking oil into the manifold at high vacuum conditions.
Black smoke: Black smoke is often a result of too much fuel and not enough air in the combustion chamber. In rare cases, it can be weak fuel pressure causing fuel to 'drip' from injectors rather than 'spray'. It can also be caused by weak fire in the combustion chamber.
Gray smoke: Gray smoke is caused by brake fluid. It generally means that your brake master cylinder is bad, and is getting sucked through the vacuum brake hose.
Blue smoke: Blue smoke is generally caused by the burning of an oil in the combustion chamber. Normal causes of oil getting into the combustion chamber are weak piston rings, bad valve guides, bad valve seals, or plugged up engines where oil is sucked back through PCV system,usually due to lack of oil changes
Sounds like you may have ruined the piston rings and this is allowing oil to seep in to the combustion chamber hence your smoke. Or if it overheated when you ran out of oil it is possible that you have a bad head gasket now. Check both your coolant and oil for signs, oil will have a white froth, or darkening of your coolant.
Hope that helps you.