Under which condition is crankshaft noise most noticeable?

• A. When the engine is cold
• B. When the engine is at low idle
• C. When the engine is hot
• D. The noise should not change with temperature or rpm

Answer: (C)

Crankshaft noise tied to how well the bearing journals are lubricated. As the engine warms up, metal expands and bearing clearances increase, and the oil becomes thinner. That thinner oil film provides less cushioning between the crankshaft journals and bearings, so the load is carried with less support and any wear or looseness is more likely to produce audible noise. Because of these lubrication and clearance changes, the noise tends to be more noticeable when the engine is hot. At cold conditions, the oil is thicker and clearances are tighter, which can dampen or conceal the same noise, and RPM variations at very low idle don’t typically override the temperature effect.