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How to Use Your Mechanic Training to Tell What the Colour of Exhaust Smoke Means

Published on February 21, 2019 by in Blog, CATI

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The smoke that’s coming out of an exhaust pipe can tell you a lot about the health of a vehicle. If the exhaust has changed colour, then it usually means that the engine is burning something that it shouldn’t be, like coolant or oil.

If you’re thinking about a career as an auto mechanic, being able to diagnose common engine problems—like oddly coloured exhaust smoke—will be an essential skill. To help you out on your journey towards becoming the best mechanic you can be, here’s how you can detect the underlying problems behind unusual exhaust smoke.

Auto Mechanics Know that White Smoke May or May Not Be Normal

White smoke can be completely normal or it may be indicative of a very serious problem. If the smoke appears light or comes out in thin wisps, it’s probably just water condensation. This is nothing to worry about and it occurs normally in engines, especially on cold days. The white smoke will usually return to normal after a couple of minutes.

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White smoke during winter is normal due to condensation in the engine

However, if the white smoke doesn’t go away or it appears particularly thick, then coolant is probably leaking into the engine. The cause is often a leaking head gasket or a crack in the engine block or cylinder. All of these problems can allow coolant into the combustion chamber. When burned, coolant emits a thick white smoke. Because coolant helps keep the engine cool, if it’s leaking then the engine is at risk of overheating, which may result in a breakdown or permanent engine damage. That’s why thick and persistent white smoke should be taken very seriously and fixed immediately.

Black Smoke Means that an Engine Is Burning Too Much Fuel

Combustion engines are designed to run on a balance of both air and fuel. When that balance skews towards burning more fuel and less air, it is referred to as “running rich.” If an engine is running rich the extra fuel being burned creates a black smoke that comes out of the exhaust pipe. This problem is typically caused by a stuck fuel pressure regulator, clogged air filter, malfunctioning fuel return line, or a leaky fuel injector.

Sometimes black smoke can impact fuel efficiency, although this will depend on the specific problem and how old the vehicle is. In newer vehicles, for example, a clogged air filter won’t affect fuel efficiency, although black smoke will still come out of the exhaust pipe. Regardless of its impact on mileage, black smoke will usually cause decreased engine performance. For that reason alone, the owner of a vehicle that is running rich should get it inspected by someone with auto mechanic training as soon as possible.

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Black exhaust smoke is usually a sign that the engine is burning too much fuel

Here’s How to Pinpoint the Cause of Blue Smoke During Your Auto Mechanic Career

Blue smoke is caused by burning oil, which means that engine oil has found its way inside the combustion chamber where it doesn’t belong. Not only is burning oil bad for the engine, but it also means the vehicle is wasting the oil it needs to keep its various moving parts well lubricated. In many cases, the valve seals, piston rings, or cylinder walls may be damaged.

During your auto mechanic career one way you can narrow down the potential cause of blue smoke is to check whether or not the blue smoke happens during acceleration or when slowing down. If blue smoke occurs during acceleration, the problem is usually a damaged piston ring. If it happens when the vehicle slows down then the cause is likely a damaged valve guide.

Are you ready to pursue a career in the auto industry?

Contact CATI to learn more about our mechanic training!

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