🔍 Key Concepts

• Color of exhaust smoke and what it indicates on a diesel (white vs black vs blue). • How cooling water leaks into an exhaust system can appear at the stack. • Typical symptoms of worn exhaust valve guides on a diesel engine.

💭 Think About

• Think about what white smoke coming from a diesel usually is composed of—what substance, and why it looks white instead of black or blue. • Which of the listed conditions would introduce that substance into the exhaust stream under all load conditions? • Consider which options would mostly change exhaust back pressure or gas flow, versus which would change what is actually being burned or carried in the exhaust.

✅ Before You Answer

• Match smoke color with whether it suggests fuel, lubricating oil, or water/steam involvement. • Ask: does this fault add liquid water or coolant into hot exhaust gases, and what would that look like? • Consider whether leaking exhaust piping joints or restricted muffler would create visible white smoke, or just noise/backpressure problems.