In preparation for winter, I've bought a snow muff, my question being, should it only be used for a start up procedure in very cold weather? What's the Temp where it should be used? And if the Landy is left to warm up, should it then be opened to allow cooling in transit. Having found out my block had a hairline crack in it due to inherited lack of Copland frost etc, I'm keen to avoid this again. However I also need to temper the chance of over heating.