IDK.
The OM for my old BMW recommends 10W-30 down to down to -30C.
We had lows down to the range you quoted last winter and my younger son's old Legacy started just fine on the HM 10W-30 that was in it.
Had I anticipated a winter as cold and as long as the one we had, I would have put something lighter in it.
We've had cars that lived outside that we started at temperatures as low as -30C on 10W-40 dinos of the mide 'eighties and early 'nineties.
Thinner grades are certainly prefered for very cold temperatures, but an engine will still start and circulate oil of thicker grades.
The OM for my old BMW recommends 10W-30 down to down to -30C.
We had lows down to the range you quoted last winter and my younger son's old Legacy started just fine on the HM 10W-30 that was in it.
Had I anticipated a winter as cold and as long as the one we had, I would have put something lighter in it.
We've had cars that lived outside that we started at temperatures as low as -30C on 10W-40 dinos of the mide 'eighties and early 'nineties.
Thinner grades are certainly prefered for very cold temperatures, but an engine will still start and circulate oil of thicker grades.