I have always only used 30 w oil in 'all' cars I have ever owned. 'Here' is socal coastal, and it snowed here the year I was born & once again in 1967. Never had a hard frost (frost is rare anyway) (rarer than rain!) I've never had the need for multi-vis oils. Originally Valvoline (old label =API CC) then to Pennzoil (old CD). Never any problems

53 chev actually used reclaimed oil 11 cents a quart!
67 VW (about 5 bugs & buses)
75 ford pu
79 VW Rabbit diesel (x2)
82 chev 6.2 d (x2)
84 MB 300 TD
84 chev blazer 6.2
83 MB 300cd
& a few others