Black smoke from the exhaust points to a problem with the fuel, which is either contaminated or mixing too heavily with oil in the engine (it’s supposed to mix, but with the right balance of oil and fuel). If it’s just a burst of smoke that then clears, then there shouldn’t be a serious problem – but it’s probably worth mentioning it to your service advisor at your next service.
If there is an excess amount of black smoke pouring out of your exhaust, then you have a bigger problem. The sensors, injection system or fuel line may not be functioning properly, all of which will need a trip to the workshop to address the problem. Leaving the problem may cause you to use more fuel than usual, as well as creating a hazard on the road and potentially making your car unroadworthy. As with blue smoke, it’s best not to keep driving with it, as any fluids coming out of the fuel line are potentially flammable.
Blue smoke usually indicates a problem with oil, and can often be confused for white smoke leading to bigger problems down the line if the right parts aren’t addressed at service. While it’s commonly called ‘blue’ smoke, it’s commonly more of a purple-grey or a very light blue.
This smoke is often accompanied by an overall loss of power, or the car struggling to accelerate. This is certainly the case with turbocharged cars – as blue smoke can also mean that the turbocharger has something wrong with it.
On a regular, petrol-powered vehicle, blue smoke from the exhaust usually means that the car is burning oil – but there can be several causes for this. There may be a leaking valve, which is letting oil get into places in the engine that it’s not supposed to, causing smoke to come out of the exhaust. If your exhaust starts blowing blue smoke, it’s best to pull over and call your roadside assistance provider, if you have one. If you keep driving, not only are you creating a hazard for other road users, any leaking oil could catch fire in your engine bay.