[Bow Tie Scottie]

My mechanic suggested to me to use 20w50 all the time because of a higher millage vehicle like mine. I use Castrol 20w50 high millage oil and will use it year round. Temperature does have an effect on the performance of the oil's viscosity and if Oklahoma's temp during winter is constantly below freezing then you might want to use a 10w30 oil. I also used Castrol 20w50 GTX in a high millage Trans-Am and it started and ran fine even when the temps were below freezing.