What is the correct way to shut down a Diesel engine?

Shutting down a diesel engine involves various steps, but the most effective and immediate method is to shut off the fuel supply. Diesel engines rely on a continuous supply of fuel to run, and by cutting off the fuel, you directly stop the combustion process, leading to a clean and safe shutdown. This method minimizes the risk of engine knock or stalling since diesel engines can continue running even after the ignition is turned off due to the fuel left in the injectors and combustion chamber.

While allowing the engine to idle for a few minutes can be beneficial for more complex shutdown procedures—such as cooling down the engine and allowing oil to circulate—you still must ensure that the fuel supply is ultimately shut off to avoid any issues. Turning off the ignition may not be effective since diesel engines can "run on" or continue functioning due to their compression ignition method. Draining the oil is not a shutdown procedure; instead, it would be part of maintenance and could damage the engine if done improperly. Thus, shutting off the fuel supply remains the safest and most immediately effective way to shut down a diesel engine.