I live in Calgary, Canada, where the ambient temperature often drops below -4F (-20C) in the winter. However, my 87 260E is either parked in my garage, or inside a heated parkade at work. When it's -4F outside,
it's +40F in the garage and +60F in the parkade. It never overnights outside and I don't ski any more, so the car is never subjected to "cold" starts. My question is what determines the correct oil grade? Is
it the ambient temperature at start-up, or the ambient temperature while driving? If the former, I could happily use single grade 30 year-round (at least in theory).
Thank you in advance,
75 FIAT 124 Spider