Blue Smoke | Caused by Oil In Combustion

Smoke that emerges blue from the tailpipe indicates that your engine is burning a significant amount of oil. Worn out valve seals or piston rings can allow oil to squeeze past and into the combustion chambers, where it will be burned along with the air and fuel. Burning a little bit of oil is okay, especially in an older car where piston ring replacement would be extremely costly. But if your car burns so much oil that blue smoke is noticeable, you may also get a dramatic decrease in power.

Cars with aftermarket performance add-ons often display blue smoke. Adding a turbocharger, for example, puts additional stress on the engine and its various seals — increasing the likelihood of an oil leak.

White Smoke | Caused by Water Vapor or Burning Coolant

On a cold winter day or when your car is just starting up in the morning, white smoke isn't a problem. This smoke isn't even smoke at all, but steam — that is, water vapor.

Overnight, condensation can collect in the exhaust which will turn into steam as your engine warms up. This will be more noticeable on cold days, but, in general steam coming from the tailpipe before the engine warms up is nothing to worry about.

When a head gasket fails, coolant can be allowed to leak past the gasket and into the combustion chambers, where it is burned. The water inside the coolant turns into steam, and then billows dramatically from the tailpipe. Burning coolant isn't a problem — but the blown head gasket that caused it is. Eventually, there won't be enough coolant left to keep the engine cool, and catastrophic damage will occur when the engine overheats.

So, if you see lots of white smoke emerging from the tailpipe on a warm summer day, pay close attention — and be prepared to pull over and stop the car if it begins to overheat.