FWIW, I have had the system freeze. I have pre-85 Westies with the water pump under the sink.  If I don’t prep the system, in the spring I’m buying a new pump. Doesn’t hurt anything else, but water freezing in the pump kills it every time.

Jim

> On Oct 14, 2016, at 9:58 PM, David McNeely <davmcneely40@GMAIL.COM> wrote:
> 
> I have never had the system freeze, and all I've ever done is drain
> everything.  Since the trap is open to the air in two directions (I leave
> the drain cap off in winter), and holds little water, it is ok -- or at
> least mine has never cracked.  The beast does stay in the garage most of
> the time in winter, but I drive it occasionally, and in below freezing
> temperatures.