Why is smoke coming from my exhaust?

 23/04/24

As a driver, there’s nothing quite as troubling as seeing smoke billowing from your exhaust pipe.

Your car exhaust system is supposed to work quietly and seamlessly. So, when it’s functioning properly, you should barely be aware that it’s there. While an occasional puff of smoke isn’t a cause for concern, seeing a large amount of smoke coming from your exhaust is usually a warning sign that something’s not working properly.

In this article, we’ll take you through the most common faults that cause a smoky exhaust, as well as how to diagnose them and when to seek help from a professional.

 

Identifying the symptoms of a smoky exhaust 

The main job of an exhaust system is to expel harmful substances and waste gases from the engine. These are released through the tailpipe as emissions and can often be accompanied by small plumes of smoke. 

It is, therefore, not uncommon to notice small amounts of smoke coming from your vehicle tailpipe, and this isn’t always the sign of an unhealthy exhaust system. However, depending on how much smoke there is, its colour and when it occurs, it could be a key indication that your exhaust system isn’t functioning as it should be. 

Let’s explore how you can diagnose the causes of an exhaust blowing smoke and when the signs indicate something more serious.

 

What different colour smoke coming out of your exhaust means

One of the ways to identify what is causing a smoky exhaust is by paying attention to the colour of the smoke. The colour of exhaust smoke often provides a good indication of engine health. 

You should also take note of when the smoke is at its worst, such as when you’re accelerating or stationery, as this can tell us more about why it occurs. 

 

What does white smoke coming from the exhaust mean? 

There can be numerous reasons for white smoke to start billowing from your exhaust tailpipe. Most of the time, it’s simply caused by condensation in the exhaust pipe, which is nothing to worry about. This usually happens when it’s cold outside, and the steam will soon evaporate when the engine warms up. 

However, if your car still produces white smoke from the exhaust when accelerating and the engine is hot, you may have an engine coolant leak, which is more serious. A coolant leak needs repairing, even if it’s only minor, so you should take your vehicle to a professional to seal the leak. If left, a leak will worsen and likely cause further damage to your engine, potentially resulting in costly repairs or replacements.

Coolant leaks can sometimes be caused by a blown head gasket, which will also cause the engine to overheat and accelerating power to diminish. If you notice any of these symptoms, you should take your car to a professional immediately, as the head gasket likely needs replacing and driving with it could lead to more severe damage. 

 

What does blue or grey smoke coming from the exhaust mean? 

As you’ll likely have guessed, blue fumes coming from the exhaust pipe aren’t normal and shouldn’t be ignored.  If you notice bluish-grey smoke coming from your exhaust, which is often accompanied by a burning smell, it usually means one thing: your engine oil is burning. 

A bluish exhaust smoke is created when engine oil somehow enters the fuel system and burns off. If you’ve recently topped up your engine oil, it may be that it’s been overfilled and is therefore leaking into the system, or you may have simply spilled the oil while refilling it. It could also be that a faulty or overly worn engine component has started to leak. 

If the blue smoke is released specifically when the car is accelerating, it’s likely due to old and damaged piston rings, which are allowing oil to enter the fuel system. In this case, the seals will need to be replaced.

If you’ve noticed blue smoke coming from your exhaust, we recommend taking your car to a professional so they can identify the source of the leak. At ATS, our expert mechanics will be able to provide a thorough vehicle inspection to diagnose the problem and advise you on necessary repairs.

 

What does black smoke coming from the exhaust mean? 

Although it looks alarming, dark, black smoke coming from your exhaust doesn’t always indicate a serious problem, particularly if you drive a diesel car. 

In diesel cars, black smoke coming from the exhaust is relatively normal and usually stops once the engine has warmed up. Black smoke is often the result of a build-up of soot caused by a clogged Diesel Particulate Filter (DPF). 

This is particularly common for drivers who only drive at low speeds, as the engine doesn’t heat up enough to allow the DFP to clean itself, allowing soot deposits to accumulate. In most cases, a long drive on the motorway should be enough to clear it. If the black smoke continues, it’s likely the DFP has become faulty or broken. You should be alerted to this by a warning light on your dashboard

In petrol cars, black smoke coming from the exhaust signals that too much fuel is being burnt, otherwise known as ‘running rich’. This may simply indicate that your air filter needs changing, but it could also be due to clogged fuel injectors or a faulty oxygen sensor. Checking these is a job best left to a professional, so we recommend taking your vehicle to your local ATS centre for our expert technicians to examine. 

If you experience excessive smoke of any colour persistently coming from your exhaust, we recommend taking your vehicle to a garage for professional attention. At ATS, our trained mechanics can provide a thorough vehicle health check to identify any faults or problems, as well as an engine diagnostic or oil and filter change. Book an appointment at your local ATS centre today.
 

Smoke coming from my exhaust FAQs

Can an oil leak cause smoke from the exhaust?

Can I drive with white smoke coming from my exhaust?