???

 

Speaking just for myself and my car it's hard to say. As you know these cars no longer have heat gauges but FWIW at 40 degrees f my heater is putting out before the first mile.

Below 40 degrees I can't address as we are below the frost line here. I couldn't resist throwing that in.

 

My XK has actually done very well in sub 40 weather. The car is stored in an unheated detached garage. It always starts on the first try. I then let it run for maybe 15 seconds before I put it in gear. It then takes about a minute for me to drive out to the main road where I run it up to 55mph pretty quick.

So far, no problems at all...