What is the primary cause of turbocharger failure on heavy diesel engines after long high-load highway journeys?

1. Shutting down the engine immediately without allowing it to idle for 2–3 minutes, which cuts off oil lubrication while the hot turbine is still spinning at high RPM
2. Driving at the statutory speed limit of 90 km/h
3. Using air brakes during normal stops
4. Keeping headlights switched on at night