I'd like to use Mobil 1 0w40 but can't find it here in Toronto. I am thinking of using a mixture of 5w30 and 15w50 (maybe 75/25 respectively). In Toronto, the coldest it gets is usually -20° Celcius (-4° F). Opinions?

TIA

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Jean

97 C280, 36k miles
96 Subaru Impreza Outback Sport, 146k miles