What is the most likely reason for white smoke coming from an engine tailpipe?

The presence of white smoke coming from an engine tailpipe is most commonly indicative of coolant leaking into the engine. When coolant enters the combustion chamber, it vaporizes and produces a white or light gray smoke. This can occur due to a blown head gasket, a cracked engine block, or a damaged cylinder head, all of which can allow coolant to mix with the engine oil and combustion gases.

In contrast, excessive fuel combustion typically produces black smoke, suggesting that the air-fuel mixture is too rich. Oil burning typically results in blue or gray smoke, which is a different color signal. A blocked exhaust system might cause backpressure issues and could lead to various performance problems, but it is not specifically associated with the production of white smoke. Thus, identifying white smoke as a sign of coolant leakage is crucial for diagnosing engine issues accurately.