There is smoke coming from my tailpipe. What do I do?

Every car, except the rare electric vehicle, has a tailpipe and gives off exhaust. However, some cars just go too far.

You see them driving down the street every day: cars with thick, smelly smoke billowing from their tailpipes. Not only is it impossible to see through and unpleasant to get stuck behind on the road, you know that what you’re seeing cannot be good for the air.

However, what do you do when your car is the offender? It all depends on what manner of smoke your car is sharing with the world.

During normal operation, the emissions from a car’s tailpipe should be invisible, but what if they’re not? Should you be worried if you notice what looks like smoke? What should you do?

Proper modern service shops employ diagnostic machines capable of pinpointing the cause of bad emissions in a matter of minutes. The cost is typically around $50. Still, there are steps you can take to monitor your car’s exhalation:

Thin white vapor: Don’t worry.

A thin cloud of white vapor that quickly dissipates after leaving the tailpipe is probably the result of normal condensation buildup inside the exhaust system. It should disappear after only a minute or two of engine operation. It may even be accompanied by a slow drip of water. This is a common sight when cars, even new ones, are first started in the morning, since condensation builds up overnight like dew on the grass.

Blue or gray smoke: See a mechanic.

Thick blue or gray smoke that doesn’t dissipate quickly is most likely the result of oil burned in the engine’s combustion chamber. It can be caused by something as minor as clogged oil passages, or it may point to something more serious that could require extensive engine work, like an oil leak caused by weak seals around the pistons.

If your engine is burning enough oil to produce visible exhaust smoke, the oil level will drop over time and require periodic top-offs. That will cost you because motor oil is not free. Worse still, burning oil can foul the engine’s spark plugs, causing breakdowns ranging from rough idle and reduced fuel mileage to hard starting and sluggish acceleration.

On turbocharged and fuel-injected vehicles, the presence of bluish-gray exhaust smoke may indicate turbocharger failure, especially if accompanied by a high-pitched whine. The turbo may need to be repaired or replaced. The oil lines to and from the turbo should also be replaced. A properly experienced mechanic will be able to take care of both.

Regardless of the cause of this type of smoke, you should have the vehicle checked out by a qualified mechanic as soon as possible.

Black smoke: First, replace your air filter. If it doesn’t clear, see your mechanic.

Black, sooty smoke is usually symptomatic of an engine that’s burning too much fuel and nearing collapse. Because engines run inefficiently when cold, they use extra fuel at start-up to ensure a smooth idle and hesitation-free acceleration. If the smoke clears up as the engine warms to operating temperature, it’s probably nothing worth your worry.

Should the smoking persist, a clogged or dirty air filter is a likely culprit. On carbureted vehicles, the choke and choke linkage could also have a buildup of gum and varnish. If the filter checks out OK, a faulty sensor, a clogged fuel injector, or another intake-system component may be the cause.

Because of the vast complexity of modern fuel-injected engines, your best bet may be to have the car checked out by a mechanic who specializes in these types of repairs.

Thick white smoke: Call a tow truck and head to your mechanic.

Unlike the wispy white vapor described above, billowing white smoke is usually an indication of serious engine trouble and warrants immediate attention.

If you continue to drive the vehicle, the engine could overheat and suffer extensive damage. Smoke of this sort is usually caused by the engine burning coolant and can be the result of a blown head gasket, a damaged cylinder head, or a cracked engine block. Such serious failures can mean a new engine or an engine rebuild, or even a new car entirely.

Even a small coolant leak can lower the engine’s fluid level, resulting in overheating and catastrophic engine damage like a seize-up. A coolant leak into the engine’s oil system may not cause any tailpipe smoke but could cause the oil to become thin and milky. Finally, the coolant can turn to brownish sludge, which is useless to your engine. These conditions also require immediate attention.

You shouldn’t panic when a little puff comes from your tailpipe, but keep an eye on it. Your vigilance and knowing what to do in these worst-case scenarios could mean the difference between a minor adjustment and a major repair.

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