Every
now and again, our cars try to tell us something by bellowing clouds of smoke
out of the exhaust. This is an issue more like to occur with older cars,
but it can also potentially happen with newer models as well.
It's
understandable if you're unsure how to react when you see some smoke coming out
your car. For instance, does a big cloud of black smoke mean your car needs
more oil? Or is the smoke a consequence of an even more serious issue instead?
Here we
tell you how to make sense of your car's smoke signals. Of course, it is always
best to take the car to a garage if you're in any doubt, but it’s good to know
a little about what is going on internally.
If
you own a diesel car and you notice smoke coming out of its exhaust, then you
can check out our seperate guide that focuses on smoke from diesel cars.
BLUE OR GREY SMOKE
If
smoke that is coloured blue or grey is coming out of your
car's exhaust pipe, this generally means that your car is a little bit too
thirsty on the oil. If you're driving a car with an automatic transmission,
make sure to inspect the oil being used by the transmission system, since a
leak here could potentially be the reason for blue smoke.
If
grey smoke is coming out all the time, you'll need to get to a garage as soon
as possible, because this could be a sign that something pretty bad is going
on. Potential issues can include a jammed turbocharger or leaking engine seals
for example. Issues such as these could be pricey to repair, but less expensive
compared to a full engine failure, so make sure to have it looked at as soon as
possible to avoid larger, costlier problems down the line.
Intermittent
blue smoke can be caused by a combination of factors, but most frequently it is
caused by worn valve seats - a critical part of the engine. This used to happen
most often on older cars built to run on leaded fuel, but which are using
unleaded instead. However, it can also happen on newer cars that are driven
particularly hard, or if they have been driven in adverse conditions with big
variations in temperature etc.
In
diesel engines, a pale blue smoke may mean that you have air in the fuel
system, which would also mean you have a problem with your fuel pump or the
fuel pipes. Blue smoke is generally bad news - the repairs are quite tricky and
not a basic DIY job. Instead, a visit to a garage will likely be necessary.
WHITE SMOKE
Instead,
it could in fact be steam from condensated water that evaporates in the hot
exhaust system. This will often happen when the engine is still cold. Once
the engine warms up and the humidity has evaporated from the exhaust system,
the white smoke disappears. Generally, this is nothing to be worried
about, though if it continues after the engine has warmed up it probably
is smoke instead, in which case you may have a problem.
If
your car has an even flow of white smoke, even when it is running nice and warm
(after, say, 30 miles), make sure you check your coolant fluid. If it's low you
may have a leak in the head gasket, a problem with the cylinder head, or a
cracked seal somewhere. The best way to avoid any of this is to make sure to
keep your cooling fluid topped up, and get to a garage when you have a chance.
It may be no big deal, but it could be serious.
If
huge billows of white smoke are coming from the car, but not necessarily from
the exhaust system, then you may have a problem with your brake fluid. The
hydraulic oil that keeps the pressure in your brake system smokes a lot when it
comes into contact with something hot (such as your exhaust system or the hot
brake discs). It may be a leaking brake cylinder or crack somewhere in the
brake system. Obviously, this can be quite dangerous, and it's worth taking
your car to the garage for a quick once over.
In
diesel engines, white smoke may signify fuel not being burned well enough due
to an injection problem, air delivery problem, or any of the problems noted
above.
BLACK SMOKE
Black
smoke coming out of your car probably means that the engine is getting either
too much fuel or too little oil.
For
cars with carburettors (i.e non-fuel-injection cars), it might be to do with a
problem with the fuel supply (more specifically a defective fuel pump, problem
with the purity of the fuel, or a blocked fuel filter). Alternatively it could
be to do with the air supply (problems with the vacuum system), problems with
the carburettor itself, or a dirty air filter that wants changing. The latter
issue is probably the simplest thing to change yourself; if that doesn't do the
trick, it may be worth having a mechanic look at it.
If you
have a car with an injection engine, then the black smoke may be due to a
problem with the injectors, the on-board computer or the sensors. Some times
turning off the engine and restarting it may reset the computer, and the
problem can go away, but generally it needs to be inspected by a mechanic.
With diesel
engines specifically, black smoke means that the engine is ’running rich’ - too
much fuel or too little air. This may be due to any of the problems above, or
just because the engine is working hard. If you are experiencing black smoke at
low load or at idling, get to a garage quickly, as it may be an early
indication of a more serious problem.
SMELLY SMOKE
Do
the emissions from your car's exhaust smell a bit like eggs? Have you noticed a
lack of power, or high fuel usage?
This
could because of a serious issue with your timing belt, the ignition system, or
something like a damaged/missing exhaust filter. Whatever the possible cause,
it's worth taking your car to a garage if it's emitting smelly smoke. Diesel
fumes are especially poisonous, so it's worth getting it checked out if only
for the sake of other road users!
