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Troubleshooting white, black and blue smoke from your car exhaust

Troubleshooting white, black and blue smoke from your car exhaust

We rely on our cars for an awful lot, so there's nothing worse than when it starts to show signs of being faulty or worn. With so many different parts that are integral to the smooth running of a vehicle, it can often be difficult to find the problem and diagnose it. But one issue that is unmistakeable is a smoking exhaust. Although there are plenty of different reasons why your exhaust might be smoking, more often than not this is down to problems within the engine.

As the engine is such an important part in getting your vehicle from A to B, if you spot any signs of it not working, it's important to diagnose the problem as soon as possible. There are a couple of different types of smoke that can come from your exhaust and leaving the problem unsolved can result in expensive or irreversible damage to your car. In this guide, we'll help you to diagnose problems with your car exhaust, as well as explaining the possible smoke colours you might see if there's an issue. We'll cover:

How to diagnose car exhaust smoke

How to diagnose car exhaust smoke

There are many tell-tale signs that your car has something wrong with it, and exhaust smoke is perhaps one of the most blindingly obvious. In most well-serviced cars, any visible emissions from the exhaust are unlikely to be anything sinister, however it's always worth checking regardless. That being said, the more severe problems are typically found in vehicles that aren't regularly maintained and where the essential engine parts have been neglected. This can be down to leaks or build ups that haven't been sorted, as well as many more possible causes which we will be explaining in this guide.

Once you've found that your exhaust is smoking, you'll need to consider whether it releases smoke when you're accelerating or when the car is stationary, as these can mean completely different things. For example, if it only happens when you've got your foot on the accelerator then your fuel mixture may be too rich in terms of how much gas you have compared to air within the combustion chamber. If your car is only smoking when it is stationary, it may just be that your car is warming up when it's cold outside and letting off some steam that's created by condensation within the exhaust system.

You'll then need to inspect what kind of smoke you're seeing. There are so many different types of smoke you may potentially see, and knowing which kinds are a cause for concern can save you a whole lot of time and money visiting garages unnecessarily.

For example, is it a cloudy white colour? Or a thick black smoke? Does it evaporate quickly or linger after it has come out of the exhaust? It's also worth considering what kind of car you have — diesel, petrol, or hybrid — as these will all react differently and therefore may put out different types of smoke to one another. Once you've looked at the smoke up close and identified what colour it is, you'll be in a better position to figure what's causing the problem.

Car exhaust smoke colours and what they could mean

Car exhaust smoke colours and what they could mean

There are a number of car exhaust smoke colours that you could see coming out of your engine, but the mains ones are white, grey, blue, and black. Below, I'll take you through the possible exhaust smoke colours you may see and what they could mean.

White smoke from exhaust

White smoke is one of the most common exhaust smoke colours. However, this isn't usually something to be concerned over.

Generally, if this is a thin, white smoke that you see when your engine is starting up, it's most likely nothing to worry about. A lot of people may mistake this as something more serious, but most of the time this can be attributed to the steam being released from your engine as it warms up during colder weather. Once your car has warmed up, this condensation should evaporate completely, and it should run as normal.

It's very important that your vehicle is given enough time to warm up as otherwise it's at risk of building up condensation in your exhaust, which could lead to exhaust leaks and rusting. This can then create expensive problems further down the line.

If you have a hybrid model, there may be a delay as to when you see the white smoke or steam depending on the amount of battery you begin your journey with. But in most cases, it still won't be anything to worry about.

Although white smoke from your exhaust is more often than not a natural part of the exhaust system heating up, there are some cases to watch out for when it can point to something more important. Dense white smoke that forms when you're accelerating and stationary it's likely to be caused by the coolant leaking into the engine. This can happen if your cylinder head gasket or intake manifold gasket is faulty, which in itself can be a costly repair job. But leaving it will only exacerbate the problem and might cause your engine to fail, which would be even more devastating for your bank account or might mean your vehicle has to be written off. So, be sure to get this checked and fixed as soon as possible.

Grey smoke from exhaust

Grey smoke can usually be linked to your car being too thirsty for oil, or it could point to a leak that's causing excess oil to burn within the engine. So, you'll need to inspect the engine oil levels at intervals to see how fast they seem to be going down. For many modern engines, this should be less than a quarter per every 5,000 miles of driving but the very newest cars will consume much less than that.

Grey smoke emissions might also be down to a faulty positive crankcase ventilation (PCV) valve, which is a device that usually draws back unburnt fuel to help control emissions. Just like any other part of your car, the PCV can wear down over time, especially when it's cold outside. However, when this happens, your engine can begin to burn your transmission fluid. Luckily, it's quite easy to check the fluid using the dipstick. If the fluid looks dark or smells burnt, it might just a case of changing this, as well as your PCV so the problem doesn't occur again. But if the fluid looks fine and changing it doesn't seem to solve the problem, you'll need to take your car to a mechanic.

If you drive an automatic car, it's worth knowing that grey smoke can point to a leak in the engine system which is drawing automatic transmission oil through it. This can be a major problem for your vehicle and will always require the help of a professional, so don't attempt to fix this yourself.

Blue smoke

Blue smoke can have causes that are closely linked with those of grey smoke. In most cases, blue smoke will signal that oil is entering the combustion chamber somewhere, meaning it's coating the exhaust rather than lubricating the moving parts like it should. This can happen for a number of reasons, including the natural deterioration of your engine elements, or another fault somewhere in the engine.

There are a couple of possible diagnoses for blue smoke coming from a car depending on the condition and last service time of the vehicle. For example, if your car has a high mileage and you spot blue smoke coming from it, this might be a sign that the valve seals or piston rings have become worn. This can result in oil getting through to the fuel system. As well as being a threat to your important engine parts, this can also be costly for you as your fuel efficiency will be significantly impacted by the leak.

Blue smoke coming from the exhaust could also mean your modulator has failed. This is an important part of the engine that controls the flow of the transmission fluid. If this fails, the fluid is sucked into the engine and starts to burn, creating the blue smoke.

If this occurs, you'll need to look at getting replacement seals. However, as a car can have anywhere between 8–32 valve seals, you'll need to take your vehicle to a professional so they can figure out which one needs replacing. As this process involves engine dismantlement, we wouldn't recommend attempting it yourself unless you're qualified.

You might also see blue smoke if you've serviced the car recently. This is usually down to putting too much oil back into the exhaust system where it's now burning off. Alternatively, it could be caused by oil being spilled directly onto the exhaust while filling up and this is being burnt as your car heats up in preparation for your drive. Typically, your car should stop smoking after a little while, but if not then you might need to go to a mechanic to have the other important engine parts looked at.

Black smoke

If you see black smoke coming from your exhaust, it could be down to a couple of things. As with most other forms of exhaust problems, the reason for this could differ depending on if you have a petrol or diesel engine. For petrol cars, black smoke from the exhaust could be a sign that too much fuel is being burnt within the combustion chamber. This can happen when your engine is not getting enough oxygen to mix together with the fuel in the combustion chamber, which may mean your need to change your air filter.

In diesel cars, it may be that the diesel particulate filter (DPF) has accumulated soot deposits over time. This important part of a diesel engine is designed to trap debris from emissions before it's released out of the car's exhaust. These soot build-ups usually occur when the car is continuously being driven at lower speeds, but a warning light should show if this is the case. Similarly, black smoke could signal that your intake manifold gasket is blocked.

How to fix a smoking exhaust

How to fix a smoking exhaust

As the engine is such an integral part of your vehicle, it's important that you try to diagnose and fix any issues with it immediately. If you don't have much knowledge about cars, then we would always recommend taking it to a mechanic who can sort it properly.

Depending on what causes the smoking exhaust, you may be able to carry out the fixes yourself, assuming you have some experience with repairs and feel confident about doing so. Below, I'll explain the possible fixes for the different colours of smoke you may see.

Clearing white smoke from the exhaust

Thick, white smoke that doesn't stop once your car is properly heated up will typically point to a crack somewhere in the exhaust system. So, it's important that you take a look under the hood to find where the problem seems to be, as leaving it can make for an expensive trip to the garage later down the line.

It'll help to keep an eye on how much coolant your vehicle is using if you suspect a problem. So, be sure to open the coolant reservoir and check the levels are correct. If your car seems to be using more coolant than normal, there could be a leak somewhere. However, be cautious that even if your car's coolant levels look normal, it's still possible that you could have a leak. This means a thorough check over of the engine must be done. If you aren't qualified to do this yourself, you'll need to take this to mechanic.

White smoke from a diesel exhaust will signal that the diesel fuel isn't burning properly inside the combustion chamber, due to a lack of heat. This can be down to a clogged fuel filter, poor fuel injector pump timing or even backed up cylinder head valves, so you'll need to have a professional clear these.

Clearing grey smoke from the exhaust

If you think the grey smoke is being caused by a faulty positive crankcase ventilation (PCV) valve, you're likely to see the burnt oil that's causing the emissions in the engine. You can also check to see if it's obstructed by shaking the valve to see if it rattles. If it doesn't, or if there's suction from the hose then you'll know it's the PCV valve that's been affected. So, the first thing you'll need to do is to change the oil. If you've never done this before, don't worry — we have a helpful guide to changing your oil that breaks it down easily for you, even if you've never done this before.

Next, you'll need to make sure you change any faulty PCV valves. This is one of the more straightforward maintenance processes you can do yourself as it just requires you to remove it from the valve hose and replace it with the new one. If you're still having issues after this, make sure you take your car to a professional to check over.

Clearing blue smoke from the exhaust

Blue smoke can be caused by a stuck positive crankcase ventilation (PCV) valve, as this will keep mixing oil in your exhaust system with air and other gases. The combustion of this mixture will cause the blue smoke. To repair this, you'll need to locate the tube which links to the intake manifold and follow it back until you can see the PCV valve. Remove it and replace with a new one.

If you think the blue smoke is down to some worn or clogged engine elements, you'll need to look under your hood. As a full cylinder head can be one of the parts behind the smoke, you'll need to know how to clean this. Simply remove the valve cover and clean it and the drain holes thoroughly, then recheck and reassemble them.

Blue smoke can also be down to failure of the modulator. This important car part is designed to control transmission shift in older vehicles to ensure fluid isn't sucked up by the engine where it then burns and produces the blue smoke. If you suspect this is the case, you'll need to locate the modulator at the rear of the transmission. You'll know when you've found this as it's connected by a small rubber hose, at one end of which is a steel tube which rises up to the engine. If you're having trouble finding it, check your owner's manual. If you've misplaced yours, no need to worry, here at GSF Car Parts, we stock a range of replacement manuals and handbooks to help you keep your car healthy for longer.

Clearing black smoke from the exhaust

If you've got black smoke coming out of your petrol car you'll need to check or replace your air filter. If this appears fine, you should also check the fuel injectors to see whether they're clogged, as well as the fuel pressure regulator. However, this can be a tricky job to do if you're not qualified, so I'd recommend taking your car to a mechanic to take a look at.

For diesel cars, you'll need to ensure the fuel and air is mixing properly to prevent soot from forming, and the best way to do this is to drive the vehicle faster. Of course, this needs to be done sensibly and you should always stick to the speed limits for any given road. But you can help to clear it by going for a long drive on a quiet road or dual carriageway where the national speed limit applies. This should clear any build-ups, which may appear as a puff of black smoke —it may even leave soot on the road behind you. After this, your engine should run much smoother and get rid of any warning lights that were previously illuminated. If the light seems to illuminate often for you, a diesel engine might not be the best choice for your driving style.

If you're considering buying or have recently bought a used diesel car, it's important to check that the diesel particulate filter (DPF) is still embedded into the exhaust system. This is because many unreliable garages looking to sell quickly will remove this to stop the problem of black smoke but doing so can mean the vehicle will continuously pump out black soot and is more likely to fail MOTs, so this can be incredibly costly for you over time. This is yet another reason why it's especially important to buy from a reputable dealer.

Diagnosing car exhaust issues isn't always simple and straightforward, but with this handy guide you should hopefully find it a lot easier to work out what's causing your car to smoke, so you can get on with fixing the problem. Whether you're a tradesman who's a dab-hand at fixing up cars or have a lot of experience working on your own car, you're sure to find plenty of helpful tips here to assist you with the job.

Here at GSF Car Parts, we pride ourselves on supplying quality parts for all makes and models of vehicle. This includes everything from essential engine parts to maintenance products, lubricants and fluids, and even tools you may find helpful when carrying out repairs. You can use our product finding tool to discover the most compatible pieces for your specific vehicle make and model.

We have plenty of other helpful guides in our knowledge hub to help you understand problems you could face with your vehicle and how to fix these when they do arise. If you'd like to speak to our experts directly, feel free to phone us on 0121 626 7971 or pop into your nearest local branch to chat with our friendly team in person.

It's always best to seek the help of a professional before attempting to work on any essential components of your vehicle such as the engine. So, if you're not qualified to carry out the repairs yourself, be sure to take your car to your local garage so a trained mechanic can remedy the problem.