Types of Exhaust Smoke:
BLUE SMOKE: Bad news because it means the engine is burning oil. The underlying cause is usually worn valve guide seals or guides, or it may be worn or broken piston rings, or worn or damaged cylinders.
WHITE SMOKE: More bad news because it means the engine is burning coolant or transmission fluid. If the white smoke is coolant, the cause is likely a leaky head gasket or a crack in the cylinder head. If the white exhaust smoke is transmission fluid, the engine is sucking transmission fluid through a vacuum hose to the transmission.
BLACK SMOKE: Black smoke coming out of the tailpipe on a vehicle with a gasoline engine is a sign of a rich fuel mixture (too much fuel, not enough air). A brief puff of black smoke may be visible during hard acceleration when the fuel mixture goes momentarily rich, but under normal driving conditions and idling the exhaust should be transparent. If black smoke is visible all the time and the inside of the tailpipe is coated with heavy black carbon deposits, it would tell you the engine has a rich fuel condition.
On an older vehicle with a carburetor, a rich fuel condition and black smoke can be caused by a stuck or misadjusted automatic choke, a leaky metal or hollow plastic float inside the carburetor fuel bowl, or a fuel saturated foam plastic float, or an incorrectly adjusted float (set too low). A restricted fuel filter may also contribute to a rich fuel mixture.
BLUE SMOKE: Usually smells like burned toast. Check the oil level on the dipstick to see if the engine is using oil and the oil level is low (add oil as needed to bring it back up to the full mark. DO NOT let the engine oil level get too low or serious engine damage will result!. You can also do a compression check or leak down test to diagnose worn pistons or rings.
WHITE SMOKE: The exhaust will have a slightly sweet smell if the exhaust contains coolant, or a burned oil smell if it contains transmission fluid. Check the coolant level and the transmission fluid level. If the coolant is low and/or the engine has been overheating, pressure test the cooling system to see if it holds pressure. If it does not, the head gasket is probably leaking and needs to be replaced. If only the transmission fluid level is low, add the required type of transmission fluid to bring it back up to the full mark, and inspect the vacuum hose from the transmission for fluid inside. If it is passing fluid, replace the vacuum modulator valve on the transmission.
BLACK SMOKE: Check the adjustment and operation of the automatic choke if the engine is an older one with a carburetor. Also inspect the air filter.
