Remember that the first "W" weight listed in the spec is only for the cold oil, before the engine has warmed up.

Pretty much regardless of season or outdoor temperature, the oil temperature stabilizes at the engine's operating temperature once the engine is warmed up.

My point is, once warmed up, there will be virtually no difference in function between 0W-30, 5W-30, and 10W-30 oils. Warmed up, they'll all function as 30 weight oil.

At the other end of the scale - in my local Connecticut area, most Volvo specialists were recommending 15W-40 year round about 15 years ago when I started driving 240's. Even with temperatures as low as 0 deg F I had no trouble getting the cars started. I've since switched all our 240's over to 10W-30 year round primarily for fuel economy reasons but the 15W-40 worked fine also.
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Sven: '89 245 NA, 951 ECU, expanded air dam, forward belly pan reaches oem belly pan, airbox heater upgraded, E-fan, 205/65-15 at 50 psi, IPD sways, no a/c-p/s belt, E-Codes, amber front corner reflectors, aero front face, quad horns, tach, small clock.