Diesels are less efficient at idle becasue they are not running at their optimum temperature. They also tend to be louder at idle because they are not burning the fuel efficiently. I saw a sticker on a company work truck one day that reminded the drivers to shut their trucks off...the sticker read "Idling gets you nowhere"...kind of has a double meaning to it.....
In regards to passenger vehicles and pickup trucks with a diesel engine, the engine will see less wear from starting and stopping than it will from idling, especially if the engine is warm. The unburned fuel at idle tends to wash down the cylinder walls of the engine and dilute the oil film on the cylinders increasing the friction of the piston rings on the wall of the engine, which over time creates blow-by that can only be corrected by rebuilding the engine. Conversely, starting and stopping the engine for short periods of time when the oil is warm, prevents the above mentioned wear, saves fuel, and besides, a starter is far easier to replace than rebuilding an engine with excessive blow by.
Has anyone noticed that Ford now has an Engine Idle Shutdown setup on the diesel trucks? It automatically shuts the truck off after a certain period of time and is mandatory in alot of states. I believe that it was introduced at the beginning of 2009 MY production.
