I'm referring to the volvo shops and other euro indi shops here in southern california. I don't know if this goes the same in other states, but all the shops I've been to use 20w50 year round. here's my understanding. 20w50 has a higher viscosity and is mainly used during the summer. the volvo manual states different oil weight for different seasons. I remember some shops saying that 20w50 is better for older cars or high-mileage cars because the higher viscosity reduces wear. I remember getting 20w50 even in cooler seasons. I've noticed here on the board many bricksters use 10w40 or synthetic. so, big question, is 20w50 ok for winter? it's been cold here, like around 60-65F. my last oil change was with 20w50. I'm due for a change, and I might do it myself and put in valvoline 10w40. but then I need to do a pcv service, so I might just end up throwing some cash to a shop for an oil service plus a flame trap service since I'm a bit wary of doing the latter myself.