If you’re seeing a lot of black smoke, your engine is running rich. What that means is that you’re burning more petrol than you should and thus running inefficiently. A number of different issues could be causing this, including faulty oxygen sensors. Lack of air entering the engine could also be a cause here, possibly from some blockage in the intake.
White smoke is coolant escaping as steam together with exhaust smoke. While not as serious as blue smoke, this is a sign that your car may be due a top overhaul as the cylinder head gasket could have failed. Don’t let this linger too long however, if your coolant burns off you’re at risk of overheating and causing serious damage to your engine.
Blue smoke on the other hand means that you’re burning engine oil – this could be the most expensive of all the smoke-related symptoms. Worn cylinder walls, leaking valve seals or failing piston rings are some possible causes of blue smoke, which are either a costly repair job or an engine replacement altogether.