Maintenance Technician Practice Test

What is the likely cause of a vehicle emitting thick, white smoke?

1. Lack of oil

2. Excess fuel

3. Coolant leaking into the engine

4. Burned out spark plugs

The correct answer is: Coolant leaking into the engine

Thick, white smoke from a vehicle's exhaust is commonly indicative of coolant leaking into the engine. When coolant enters the combustion chamber, it vaporizes and exits through the exhaust system, creating a noticeable white smoke. This situation usually serves as a warning sign that there may be a problem with the head gasket, a cracked engine block, or a damaged cylinder head. These issues can lead to significant engine damage if not addressed promptly, as the presence of coolant in the engine can disrupt the combustion process and result in decreased performance. In contrast, the other options do not produce white smoke. A lack of oil typically results in engine knocking or overheating, excess fuel usually leads to black smoke, indicating rich fuel mixture problems, and burned-out spark plugs may cause engine misfires or rough running but would not result in colored exhaust smoke. Understanding these distinctions helps in accurately diagnosing engine issues based on smoke color and characteristics.