BLACK OR DARK SMOKE
able to perform a compression test to see if an overhaul is necessary before you commit to it.
A test you may perform to confirm which parts are worn is to use the rear view mirror. If you notice the smoke in your mirrors as you decelerate (after accelerating fairly hard) the culprits are in the valve train, i.e. valve seals and/or valve guides.
A car with worn piston rings will smoke heavily under hard acceleration, which means a bigger repair bill.
If your car smokes under both instances, you will have a bigger repair bill. It is easier to have a friend to observe the incidences (if you are not confident) as using the rear view mirror while driving alone may result in an accident (and a big, big repair bill).
If there is a distinct burnt oil smell, you may have transmission oil entering the intake manifold through the vacuum modulator. Replacement of the vacuum modulator is simple and cheap.
If there is a different sort of smell, it may be that the cylinder head gasket is failing. Check your coolant levels to confirm this. Repair involves a top end overhaul to replace the head gasket.
Black smoke from the exhaust is bad news. It may disappear after warming up and be less noticeable but it will need to be addressed.
The engine may or may not be running rough or misfiring. Possible causes is that the choke may be stuck closed (an easy fix) or the air filter is seriously clogged (also an easy fix). But if the two items are okay, you may have an ignition problem (that is easy to fix on older cars).
Replacement of parts such as the ignition coils, distributor, condensors or contact points on older cars are easy and quite cheap but on a modern car, it may involve a pricey ECU replacement and/or tuning to suit.
A definite symptom of this smoke is a tendency for the car to use more fuel than usual, burn out spark plugs regularly and a general lack of power.
Other things to check are the ignition timing (on older cars). A leaking head gasket may also be indicated by a drop in coolant level and subsequent overheating. Partially stuck injectors as well as a faulty fuel pressure regulator may also create black smoke. Your foreman will be able to diagnose and troubleshoot the problem.
Diesel car owners may feel left out but the same still applies since newer diesel cars tend to emit very little smoke. Turbocharged car owners have more items to go wrong and smoke is usually a bad sign for the health of the turbocharger unit.
In conclusion, anytime you see smoke in your tailpipe is a bad sign for the health of your wallet. Unless you own a twostroke Saab, of course.