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What exhaust smoke means for you and your car

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Updated 10 Oct 2019

Jonathan Nash

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How do you know when your car is feeling under the weather?

A shudder here, a tremor there, an unfamiliar noise, squeak or rumble – if you’re paying attention and you know the quirks of your car’s behaviour, there are plenty of signs that will give you an inkling that things are not well with your four-wheel pride and joy.

There is one sign, however, that even the most inattentive of drivers can’t miss - smoke.

Generally speaking, your car should not be coughing up smoke like some misguided teenager trying to get through their first Winfield Red, and there is no circumstance in which billowing clouds of the stuff is a sign your car is in good working order.

However, while any type of smoke coming from your exhaust means trouble, the colour – blue, grey, white or black - can give you an idea of what that problem might be.

So, what do those different colours mean for you, your car, and your wallet?

Firstly, while the smoke is coming from the exhaust system, it is unlikely that is where the problem lies.

The exhaust system is simply a means of expelling the gases created by the ignition of fuel and air in the engine and so it’s at the front end, rather than at the tailpipe, where investigations should start.


Blue smoke usually indicates burning oil and can mean there is a degraded seal or busted piston ring that has allowed oil to seep into the engine combustion chamber.

Alternatively, if your vehicle is turbocharged - which is becoming much more common on modern cars - then the cause might be traced back there.

A turbocharger works by forcing air into the combustion chamber. Like all moving components in an engine, it uses oil for lubrication and any seal problem may cause that oil to leak into the turbo and be blown into the chamber.

Turbochargers are actually considered to be pretty reliable pieces of kit, so blue smoke is more likely to be caused by oil leaks in the engine proper.

However, you’ll want to be sure as either way there’s a pretty serious problem going on and one that could, if left to fester, be expensive to repair.


Thick grey smoke could be the result of a couple of issues. Like blue smoke, it can be an indication your car is burning oil or that the turbocharger is playing up (see above for possible suspects).

It can also indicate that transmission fluid – the stuff that lubricates the components of the transmission system - is leaking and burning off.

Once again, left too long, a transmission fluid leak will turn from a minor problem into something of a whopper, so don’t tally over a visit to the workshop.


While many vehicles blow out a bit of white smoke when starting and warming up, that short burst of fog is nothing to worry about – it’s just a bit of condensation steaming off.

Clouds of white smoke belching from the tailpipe is another issue altogether.

It’s an indication that the engine is running hot and the cooling system is on the blink.

These problems could include a coolant leak, a cracked engine block or an issue with the head gasket – all of which are of major concern.

The head gasket, for example, is the component that sits between the engine block and the cylinder head – the two pieces that form the core of the engine and are where the pistons, cylinders and combustion chamber are housed.

A problem with the head gasket is pretty epic and you may well have have heard the phrase ‘blown a head gasket’ being used to convey the colossal nature of a problem.

When it comes to your engine, this is not an exaggeration.

It can be a real wallet-buster if not treated swiftly.

So, if you see a lot of white smoke, get to a mechanic . . . immediately.


Black smoke means the engine is burning too much fuel.

That is to say that too much fuel is being injected into the combustion chamber.

A few possible culprits here, including fuel sensors, the injection system and the fuel line.

The air filter is on the list of suspects too.

It is designed to prevent debris and contaminants from entering the combustion chamber, so a clogged filter means less air making it through and the fuel mixture becoming too rich.

This leads to reduced performance and, eventually, will cause damage to the engine.

Best to get the problem diagnosed and fixed early.


There is no good reason to ignore the smoke coming from your car.

Whatever the colour, it’s a tell-tale sign that you’ve got a potentially serious problem on your hands.

There is, as the saying goes, ‘no smoke without fire’, and that ‘fire’ could burn a hole in your wallet as well as your engine.

Get a mechanic to diagnose and repair the problem as soon as you can.

Let AutoGuru help you quickly and easily book a high-quality mechanic to sort out your smoke problem. 

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Written By

Jonathan Nash

Jonathan has been writing about the auto industry for years and is particularly interested in the high-tech innovations sweeping the industry.

He’d love to own a Tesla Model S, but also adores anything with a V8 under the bonnet. 

He has yet to decide between an EV or a Mustang for his next ride.