the pink RV stuff clearly states for plastic pipes (not for engine internals). I use it to flush my RV. But have seen boat dealers use it for winterizing.
I was using this Merc -50 stuff cause it had corrosion inhibitors and never had any problems. The pic below shows what happens at -40C. It got slushy but could still shake it about. The jug never expanded. Even though it didn't go solid, after seeing that I started flushing and left the internals dry/drained.