Just do it. I cut out an old post of mine:
"Ok, my five öre, as we say here:
2. In my experience, at actual -30 to -40 celsius, fresh good 5w or even 10w will pump. But it will take longer to reach all spaces. So pick an oil with lowest pour point possible like an extreme 0w. Check the data sheets, since there is no lower tag than 0w you will see some variance within that class.
3. Does your engine reach normal operating temps in the cold? If it does, you don't have to lower the hot visc. If it doesn't you may want to lower the hot viscosity a snap or two. Or, as I do here, put a winter cardboard sheet over like 2/3 of the radiator to reach temp and get warm quicker.
4. Get a block heater with an outlet and heater inside the vehicle for heat there too. We use
http://www.defa.com/en/html/fp/
5. In temps like -30 celsius, everything starts to act differently, plastics snap easier, mechanical parts rattle more, part fit deteriorates, so generally things break more frequently in the cold. Nothing to do, but keep it in mind and take it easy with the cars.
As a secondary point, you will also freeze. Keep something warm in the car, like blankets, for the event of a breakdown or accident that may keep you out longer than the car will run. Stay safe.