We use two steps: 1. Insert a medical-grade endoscope through the spark plug hole to visually inspect cylinder wall scratches and carbon buildup on the piston top; 2. Extract an engine oil sample to check for large metal debris or emulsification (caused by coolant leakage).

Experience turbo lag and power surge during road tests; check for significant oil accumulation at the turbo intake and intercooler connections (slight oil vapor is normal); and use OBD to read the real-time boost pressure peak to see if it meets factory settings.

Completely different. The assessment of commercial vehicles focuses on: the extent of wear/deformation in the cargo area, whether the frame has been twisted due to overload, the fatigue of the leaf springs, and the emissions of the diesel engine. Minor exterior scratches carry very little weight in the assessment of commercial vehicles.