Originally Posted by DocBrown
At 32 the lines will not freeze solid, they might get slushy....
Just to get nit-picky, standing water does not 'turn slushy'. Liquid water crystalizes into ice as the molecules give up enough heat to the surrounding air.
If the pipeful of water is exposed to temperatures of 32F or lower for enough time, all of the water will solidify and expand; blowing apart the fittings at each end or splitting the pipe. Considering PEX's inherent flexibility, I expect the hard plastic connectors will fail first.
Once that happens, enough water will leak out of the whole system during the next thaw so you only have one or two fittings to replace come springtime.