I idle when it gets about 10 degrees or lower. Yes I have an APU. Yes I have an estar heater......Yes I treat my fuel. BUT.......the filters still can was and tell because of the #### bio diesel blends. Depending on the fuel distributed the blend can vary. Also......don't trust the big truck stop chains to treat their fuel on a consistent basis. I don't idle very much. But when it gets stupid cold out I will idle. Better off idleing than finding out your gelling issue when you finally get on the big road and you start to sputter.