Car exhaust smoke and what it means

Sunday September 25 2011

By Mustafa Ziraba

So you are driving in traffic jam, but the cars from the opposite direction are moving fast. You then see this truck oozing thick smoke from its weirdly placed exhaust pipe coming your way very fast. It hits you that this truck’s fumes are going to blast you in the face, you then hurry to up your windows only to let some in. You then wonder what kind of maintenance this truck is getting or any other car for that matter with lots of smoke coming out of its exhaust.

Smoke from the exhaust is not good news, but does not necessarily mean the engine needs re-building. First, you need to determine what colour of smoke is coming from the exhaust. The three most common colours of smoke include white, blue and black that I’ll look at in more detail. If you have red or yellow smoke, you could be driving a spaceship.

White smoke is caused by water and or coolant entering the cylinder, and the engine trying to burn it with the fuel. The white smoke is steam. There are special gaskets (head gaskets are the primary gaskets) that keep the coolant from entering the cylinder area which could have failed.

Blue smoke is caused by engine oil entering the cylinder area and being burned along with the fuel air mixture. As with the white smoke, just a small drop of oil leaking into the cylinder can produce blue smoke out the exhaust. Blue smoke is more likely in older or higher mileage vehicles than newer cars with fewer miles. You might need replacement of these seals or use oil specially designed for old and high mileage engines.

Black smoke is caused by excess fuel that has entered the cylinder area and cannot be burned completely. Another term for excess fuel is “running rich.” Poor fuel mileage is also a common complaint when black smoke comes out of the exhaust. Black smoke is the least cause for alarm. Excess fuel will usually effect engine performance, reduce fuel economy, and produce a fuel odour. Black smoke is also more common in older diesel engines caused by numerous things, including but not limited to dirty air filters, fuel injectors, a turbocharger malfunction as well as poor fuel quality.

Smoke should be regarded as an opportunity to take measures that will save you money in both the long term and short term. At the least, smoke may be due to a simple problem, which is causing poor combustion efficiency and costing you in excessive fuel bills. At the other end of the scale, though, smoke may be your last chance to act before a catastrophic engine failure occurs.

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