Is it a good idea to idle truck at "feels like -9F"?

If that were true you wouldn't need winter fronts or shutters. Shoot objects with thermal temp guns and you will see that something that is on the wind side of things will be colder than something on the protected side regardless of ambient temp. That is why you don't want to park nose in the wind. Aluminum fuel tanks will be colder than steel in the same conditions too because aluminum is more of a heat sink while steel holds it better.

 

Wind doesn’t make anything colder. Ambient ambient temperature is ambient temperature. It’s that simple. The wind can just bring ambient temperature to an object that is warmer and pull away whatever he is coming or came from that object. If the object is already an ambient The wind can just bring ambient temperature to an object that is warmer and pull away whatever he is coming or came from that object. If the object is already an ambient temperature, there will be no change. The wind dam is to keep the heat that the engine produces within the hood area. All the wind will do is push ambient temperature directly to the engine. Same thing when parking away from the wind. If you look at a truck with thermals, you will see the heat around the truck. This is the heat that is from operating the engine and Frictional heat caused by the transmission and differentials. If there is a strong wind, it will blow ambient air to the gaps and push the warmth away.

 

Wind make YOU colder, because moving air cools you off much faster than still air. Your body doesn’t care what the air temperature is, it cares about what the body temperature is! Wind will also pull the warmth out of anything that isn’t insulated, like, say, truck windows.

The coldest I’ve ever been was when I got soaked in a 35° F rainstorm. Instant hypothermia!

As for idling, my company recommends that we idle whenever the outside temperature drops below 15° F.