They are made to do that.
Built in high idles to keep things warm enough.


phox

 

You will rarely see a trucker idle his truck without speeding it up.

 

OTR truck extended idling is rapidly becoming a thing of the past. Not only is extended idling illegal in 32 states now but the feds are likely to start giving short term low interest loans to truckers who install auxiliary power units (APU) for semis real soon, some states are already doing it. A typical OTR truck spends $700-$1000 per month on idling fuel while a APU burns less than $100. Pretty obvious which method puts more money in the trucker's pocket. This is expected to cut oil consumption by over 20 million barrels per year in the US plus reduce emissions, noise and engine wear.

Typical APU
http://www.auxiliarypowerdynamics.com/