ABYC Diesel Practice Exam

What does white smoke from an engine only when cold typically indicate?

1. Excessive fuel pressure

2. Faulty pre-heat device or partially vaporized fuel

3. A clogged air filter

4. A need for engine oil change

The correct answer is: Faulty pre-heat device or partially vaporized fuel

White smoke from a diesel engine, particularly when it is cold, often arises from issues related to the fuel injector or combustion process. The correct answer revolves around a faulty pre-heat device or partially vaporized fuel. In diesel engines, starting in cold conditions requires efficient combustion of fuel. A pre-heat device, such as glow plugs, is critical in warming the combustion chamber, allowing for proper fuel ignition. If the pre-heat device is malfunctioning, the fuel may not vaporize adequately, leading to incomplete combustion. This results in an abundance of unburned fuel entering the exhaust system, manifesting as white smoke. Additionally, partially vaporized fuel can also contribute to this phenomenon, as it indicates that the fuel isn't being properly atomized, further hindering the combustion process. When the engine warms up, the issue typically resolves itself as combustion efficiency improves, and the smoke dissipates. The other options, while they might indicate problems in different scenarios, do not specifically correlate with the presence of white smoke in a cold engine startup condition as effectively as the issues associated with the pre-heat device or fuel vaporization do.