Originally Posted by Pierre Louis
Modern premium diesels have an electric coolant heater that in cold weather brings the engine to operating temp faster and allows for the cabin heater to work. The rest of the benefit of a grill cover in winter may just make it easier for the thermostat/system to work, but perhaps may not be necessary. Can't think of a reason it would interfere with anything in the dead of sub-zero winter, so it shouldn't hurt. I would be careful not to overheat the all-aluminum engine if the temperature becomes more human.
So far everything has been working pretty well without, but when it gets down below -10F it does seem to affect the heat somewhat. It could be me just needing more heat than what I am getting. I think TDIWyse was covering his grill and monitoring the coolant temps which is why I asked the question.
On gas vehicles I never did this because they run less efficiently and they had a lot of excess heat to share but I find that the diesel does not throw heat like our gas running BMW in the same temperatures.