[RKDinOKC]

Most of the newer diesels manuals say to NOT let them idle after startup for more than 3 minutes.
They also say to shut them off it you are going to let them set for longer than 1 minute and it only takes the turbo a max of 30 seconds to cool down after being driven hard. The only exception being a 7.3 Liter, for some reason they have problems hot starting in situations like ambulances. Drive like heck to pick someone up. Shut down immediately without it cooling at all, then after the short time to load the patient up it won't start.

Idling they burn a gallon an hour. And cool off enough idling that it gets an incomplete burn and starts washing the cylinders, etc.

Refrigeration trucks are different, the idle is set higher to take the load of running the refrigeration units and keep the engine warm enough to burn and lubricate properly.