A quick search online of the major diesel engine manufacturers all say do not idle the engine for more than 5 minutes. Some of the engines now even have automatic shutdown timers to turn the engine off. They all talk about excessive engine wear, wasted fuel, decreased oil life, and increased air pollution caused by excessive idling.
Of course the biggest reason many still do it is....."but we have always done it this way."
Times have changed for gasoline and diesel engines and the old ways are no longer relevant.
