[Bogie]

I often wash with ambient water temp, even in the 30s. However, I sometimes keep my soap buckets warm. Think about it. When you get the car wet before wash, and rinse afterwards you aren't really touching the water...so what's to care? Just keep the wash buckets warm (fill up inside), and most of the washing is nice and warm to touch.

I would advise against washing below freezing even with hot water unless it's carefully applied and dried. This also applies to above freezing washes when the dry period extends below freezing. There are all sorts of nooks and crannies where water can pool and freeze, regardless of how warm or hot it may have been when applied.