Understanding the Reasons Why Your Car Is Blowing Smoke From the Exhaust!

If you start your vehicle and see large amounts of smoke coming out of the exhaust, there are a few reasons for this. Unfortunately, apart from one issue, it means a relatively severe and costly repair.

However, you shouldn’t panic if the smoke only appears on start-up and disappears once the engine warms. It’s caused by condensation in the exhaust, especially on cold mornings, which goes away as soon as the vehicle reaches operating temperature.

The bad news is if the smoke from the exhaust doesn’t go away, there is a problem that needs rectifying. I have included the most common causes in this article.

Reasons for Excess Smoke Coming Out of the Exhaust

If you find abnormal clouds of smoke coming from your exhaust, first, you need to determine what color the smoke is. Then, you can start to narrow down the cause using this list: 

White Smoke:

  • Coolant Leak – If the smoke is white and smells sweet, it might be due to a coolant leak. A blown head gasket, a cracked engine block, or a damaged cylinder head could cause this. Regardless of how the coolant is getting in, the white smoke indicates that the coolant is getting combusted. You can verify this by checking the coolant level, which should have dropped. 
  • Condensation – In some cases, especially during cold weather, white smoke could be condensation in the exhaust system. It’s usually more visible when the engine starts and should dissipate as the car warms up.

Blue Smoke:

  • Oil Consumption – Blue smoke typically indicates that the engine is burning oil. This could be due to worn piston rings, valve seals, turbo failure, or a malfunctioning PCV system. The oil gets into the combustion chamber and burns with the fuel, resulting in blue/grey colored smoke. When valve seals fail, the smoke coming out of the exhaust is like that of a steam train, which is obvious. Whereas if its a turbo failure, it will just have a blueish tint to a little more smoke than usual. 

Black Smoke:

  • Rich Fuel Mixture – Black smoke often indicates the engine burns too much fuel. This could be caused by issues such as a clogged air filter, a malfunctioning fuel injector, a faulty oxygen sensor, or problems with the fuel pressure regulator. When too much fuel is added, the combustion process cannot be completed, and you get clouds of black smoke coming out of the exhaust. This type of fault can sometimes be cured using a fuel treatment specializing in cleaning injectors. 

What Should You Do if You See Clouds of Smoke Coming From the Exhaust?

Apart from condensation, all of the reasons for excessive coming from the exhaust require a large amount of investigatory work to determine the exact cause, which may require using specialist tools or disassembling the engine. For these reasons, I strongly recommend driving your vehicle straight to a mechanic for inspection. If you catch some of these issues early, they may not be as bad or costly as you think to rectify. 

How Much Exhaust Smoke Is Normal? 

When you first start driving in the morning, you can expect a bit of extra smoke, especially on cold days; after a few minutes, this should return to normal. Regular exhaust smoke should be clear, though it may have a slight tint. I usually describe normal exhaust smoke levels as no more than seeing your breath on a cold day. The smoke should not be seen a few moments after coming out of the exhaust; if the smoke cloud remains, the engine is also burning, something else, highlighting there may be an issue. 

Can You Drive With a Lot of Smoke Coming Out of the Exhaust?

Driving with smoke from the exhaust is possible; however, the risk of damaging more components is exceptionally high.

If the problem is the head gasket, eventually, the car will overheat, and it will do so within a minute or so of starting the engine, so it will not be possible to drive more than 100 yards.

With an oil-related problem, the car will be chucking out vast clouds of blue smoke, requiring the oil to be topped up regularly; there is the danger you may run out of oil, which will also cause damage to the engine. Although this may not bother you so much in your car, blue smoke from an oil-related problem will contain oil droplets, which won’t be nice for the car or motorcycle traveling behind you.

You may be able to continue driving with black smoke for longer than the other issues, however too much fuel being burnt will cause the engine to overheat and fail quickly. So I strongly recommend you don’t.

Frequently Asked Questions

Can Low Oil Cause Smoke To Come Out Of The Exhaust?

Low oil on its own will not cause excess exhaust smoke. Low oil can cause burning in the engine, and smoke can be evident in the engine bay, but there will not be a significant amount exiting the exhaust.

Does White Smoke Mean A Blown Head Gasket?

The most common cause for pure white smoke is a blown head gasket. The head gasket seals the block and head of the motor together, allowing the coolant to flow through the water jackets. When the head gasket leaks, the coolant is allowed to get into the combustion chamber, where it is burnt, resulting in significant amounts of white smoke.

Final Thoughts

Unless you are experiencing white smoke until the engine warms up, it will probably be another issue. A coolant leak caused by a failed head gasket is quite a common problem. Some vehicles are known to have more head gasket failures than others, so it is good to be aware of this. If your car puts out a lot of smoke, and you can’t identify the cause from the list above, have your vehicle inspected by your mechanic, who can help.

My name is Tom although my friends call me Tommy. Messing around with cars and bikes has always been a hobby of mine even from a young age. So I made it my day job 17 years ago. I am a fully qualified mechanic as you would expect. I've worked in all different areas of the motor trade, valeting, panel beating, engine repairs, I'm sure you get the idea. I enjoy sharing my wealth of knowledge and experience with others, which is the reason I spend a lot of time here writing for this website.

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