What are the impacts of leaving the car running for 4 hours without turning it off?

[River]

The impacts of leaving the car running for 4 hours without turning it off: First, it will affect the engine. If the vehicle remains in a parked but not turned-off state for a long time, the engine will operate at low RPM for an extended period, increasing carbon deposits on the piston and valves, leading to unstable idling or other adverse effects. In severe cases, it may even affect the engine's lifespan. When the engine operates at low RPM, the leakage between the valves and piston rings increases, and the intake vortex weakens, resulting in poor fuel atomization and incomplete combustion. The contact time between the combustion gases in the cylinder and the cylinder wall increases, raising heat dissipation losses, and oil mist becomes difficult to disperse, significantly increasing the engine's fuel consumption.