Cars, Caravans and Other Vehicles

Blue, White, and Black: What Can a Car's Exhaust Smoke Colour Tell You?

A cloud of smoke spewing from the exhaust of a vehicle is an obvious sign of trouble, but the underlying issues can be hard to pin down. One way to identify the probable cause is by checking the colour of the smoke, then reading through this list.

Blue Smoke

Blue smoke is often seen as less serious than more visually-ominous black smoke, but often indicates more serious problems. Blue smoke is a common sign of engine damage, and will often occur when oil is leaking. Instead of being used to lubricate the moving parts of your vehicle, it can leak into the combustion chamber of the engine and starting being burned along with the fuel. Broken valve seals or piston rings and worn cylinder walls can all be the cause of blue smoke.

However, there is an exception. If your car uses a turbocharged engine, it could be that blue smoke is produced because there is something wrong with the blower. In either case, you'll need to see a professional mechanic as soon as possible.

White Smoke

It's often hard to diagnose whether white smoke is a problem; in fact, white smoke is often nothing but steam. It is simply discharged when a cold engine is becoming warm, and is a natural part of the fuel combustion process. On particularly cold mornings, this may be more noticeable, but you shouldn't be seeing anything after you've travelled a mile or two.

That said, actual white smoke is a problem. You can usually tell the difference because smoke will be much thicker and produce a more noticeable odour. White smoke is less common than grey or blue, and is usually caused by either a small leak of coolant, which can cause overheating, or a blown gasket.

Black Smoke

Black smoke looks pretty bad. In fact, many people see it as the kiss of death for their favourite set of wheels. However, black smoke usually indicates nothing more serious than that your car is burning through too much fuel.

If your car is emitting black smoke for this reason, you'll probably notice a marked drop in efficiency, and possibly a smell of fuel while you're driving. If this smell is strong upon start-up, call for a tow instead of driving to your mechanic – it usually means that a significant amount of fuel is leaking somewhere inside the vehicle.  

If your car exhaust begins emitting clouds of smoke, no matter the colour, consider it a clear red flag. See a professional mechanic immediately to set the problem straight before it can develop into something more serious.


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