Just looking at my owner's manual this morning says to use 15W-50 for temps. from -20C (-5F) to 100F. It goes on to say that ambient outside temps. can go above or below the SAE grades for short periods without problems. Now, I believe these numbers were derived with using conventional oils since looking at synthetics such as M-B's specs of Pour point -45C (-49F) and Pumpability limit of -37C (-35F). Does this mean it's safe to use all year? I'm in Toronto and it rarely gets to below -20C....and even if it did a couple degrees, would it matter?