there is a manual in the manuals area (accessable by donating to the site)

manual states
constant use below -12C
5w20, 5w30, 5w40

may be used as low as -12C
10w30, 10w40,10w50, 5w20

above 0
10w30 10w40 20w20 20w30 20w40 20w50

so its within spec