5KT: Oil for -30F winters?

[smitht@unb.ca (Tim Smith)]

Any suggestions re: oil weight for cold weather.  It's an '86.  Do I drop to
5W30 or is 10W40 the limit.  We may see -30F for say 10 days straight, then
warmer, 0->+10F.   Car will be making hour long ski-hill trips at <70mph,
any probs with thinner oil? Prefer changing dino oil + filter every 2.5K
miles, so no synthetics thnx.

Oh, and can anyone tell me the size of the hex key I'll need to get of the
cap in order to pull out the front shock cartridge?

tia, Tim Smith