My Car Smokes From the Exhaust Pipe. What Does This Mean?

Reader Question:
My car frequently smokes from the tailpipe; does this mean I need an
engine overhaul?
Thank you, Don.

Dear Don,

Good question Don. Smoke coming from the
tailpipe is not good news, but does not necessarily mean the engine
needs rebuilding. First, you need to determine what color of smoke is
coming from the tailpipe. The three most common colors of smoke that can
be emitted from the engine and billow from the tailpipe are as follows:

White smoke: White smoke
is caused by water and or antifreeze 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
antifreeze from entering the cylinder area. The cylinder is where the
fuel and air mixture are being compressed and burned. Any amount of
antifreeze that enters this area will produce a white steam that will be
present at the tailpipe area.

If white smoke is present, check to see
if the proper amount of antifreeze is inside the radiator and the
overflow bottle. Also check to see if antifreeze has contaminated the
engine oil. You can look at the engine oil dipstick, or look at the
under side of the engine oil filler cap. If the oil is contaminated with
antifreeze, it will have the appearance of a chocolate milkshake. Do not
start the engine if the oil is contaminated with antifreeze, as serious
internal engine damage can result.

How did antifreeze get in the oil or
cylinder in the first place? The engine probably overheated and a head
gasket failed due to excessive heat, thus allowing antifreeze to enter
the cylinder (Where it is not meant to be).

Blue Smoke: 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
tailpipe. Blue smoke is more likely in older or higher mileage vehicles
than newer cars with fewer miles.

How did the engine oil get inside the
cylinder in the first place? The car has many seals, gaskets, and
O-rings that are designed to keep the engine oil from entering the
cylinder, and one of them has failed. If too much oil leaks into the
cylinder and fouls the spark plug, it will cause a misfire (engine miss)
in that cylinder, and the spark plug will have to be replaced or cleaned
of the oil. Using thicker weight engine oil or an oil additive designed
to reduce oil leaks might help reduce the amount of oil leaking into the
cylinder.

Black Smoke: 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 tailpipe. Black smoke out the tailpipe is the
least cause for alarm. Excess fuel will usually effect engine
performance, reduce fuel economy, and produce a fuel odor.

How did the fuel get into the cylinder in
the first place? Some of the causes of excess fuel are a carburetor that
is out of adjustment, a faulty fuel pump, a leaky fuel injector, or a
faulty engine computer or computer sensor. If black smoke is present,
check the engine oil as in the white smoke example to make sure excess
fuel has not contaminated it. Do not start the engine if a heavy, raw
fuel smell can be detected in the engine oil. Call your mechanic and
advise him of what you have found.

I hope this helps you determine what
could be causing your engine smoke, and the possible reasons behind the
smoke.