Diagnosing a problem through your exhaust pipe

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The exhaust coming from your car's tailpipe can tell you a lot about what might need to be fixed. Image: Flickr / dagoaty / CC-BY

The exhaust that your vehicle puts out can tell you a lot about how the engine is functioning. If the exhaust coming out of your vehicle starts to look or smell differently than normal, that difference can help you diagnose the problem.

Blue smoke

If blue or bluish smoke is coming out of your vehicle’s tailpipe, the likely reason is burning or smoldering oil. Oil is used throughout the engine to lubricate moving parts, and it can get into the combustion chamber of the vehicle and create blue smoke in a number of ways. The most likely places the oil could be making it into the combustion chamber are the valve seals, valve guides, piston rings, cylinder walls or crankcase ventilation system.

Light gray smoke

If your exhaust pipe is putting out gray smoke, then the engine is likely burning coolant or antifreeze. Generally, there will be a sweet or acidic smell when antifreeze is being burned. Coolant can get into the combustion chamber through three major areas. The cylinder head or engine block could crack, which would allow coolant into the combustion chamber. A cracked cylinder or engine block can be very difficult, even impossible to repair. A blown head gasket is also expensive to repair, so be sure to ask your mechanic for a detailed quote before you agree to any repairs.

Black or dark gray smoke

If very dark smoke that smells very foul is belching out the back of your vehicle, then it is an indication that your car is burning too rich of a fuel mixture. Rich fuel mixtures not only cause more pollution, they indicate a larger problem with your fuel system. Leaking fuel injectors, a bad fuel return, a fuel pressure system out of balance and a variety of other factors can all cause a fuel mixture that is too rich for the vehicle’s engine.

The difference between steam and smoke

When you first start an internal combustion engine, it is normal for some amount of steam to come out of the tailpipe. This clean, white steam will not smell bad and will stop coming out of the tailpipe in a matter of moments. It is normal for steam to come out of an engine, but it is not normal for smoke of any description to come out of your tailpipe. If you are not sure, ask a friend to watch as you start up or run your vehicle outdoors. Never run a vehicle in a closed garage.


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