I am sure that some on here, in even colder climes than I am in, use the T6 year 'round with no seemingly ill effects, but I would not use anything that viscous in the winter in my FiST unless I were open tracking it every day, or it had a decently high viscosity index (like the Red Line 0W-40 does).
It DOES have a fairly high starting TBN (being a 'diesel type' HD oil), so it would help with the winter short trip, DI fuel dilution 'washdown' of the sump oil, but still way too thick on start-up in the 0*F (or lower) to 20*F ambient temps, in my opinion (yup, despite the 5W rating!).
Next year, for the winter OCI, I will try the Sustina 0W-20, regardless of price, again, IF I can even find it!
(I already did my winter OCI for this year with Amsoil Signature Series 5W-20.)
It DOES have a fairly high starting TBN (being a 'diesel type' HD oil), so it would help with the winter short trip, DI fuel dilution 'washdown' of the sump oil, but still way too thick on start-up in the 0*F (or lower) to 20*F ambient temps, in my opinion (yup, despite the 5W rating!).
Next year, for the winter OCI, I will try the Sustina 0W-20, regardless of price, again, IF I can even find it!
(I already did my winter OCI for this year with Amsoil Signature Series 5W-20.)