One thing has never changed with a diesel engine, at idle, they use more air than fuel during a cold engine startup. Your diesel engine uses (depending on make) glow plugs, intake heaters, or a mix of both, to help aid in starting in the morning or during cold ambient temperature startups.
These starting aids also help with another area of your truck – tail pipe emissions are improved by increasing intake air temperatures. The hotter the incoming air flow is to that cylinder, before it ignites, the cleaner the burn. These “starting aids” do not run all the time, there are exceptions, but usually after town minutes of idle time these heaters are shut off. Once these heaters “starting aids” are shut off, the cylinder temperatures cold down due to all of the incoming air drawn in and the small amount of fuel used to keep the trick at idle.
If you’re going to run extended idle times when cold, be sure to have an elevated idle. Some trucks, if cold enough, will have this enabled automatically after a certain amount of idle time is achieved. Older trucks will have to have something built in, or a brick on the pedal. This way the engine will build heat more efficiently than if at idle.
