I have used Pennzoil multi-grade oil in my GM V-8s and like the brand alot. The cars are high mileage so I' m trying the High Mileage Pennz now. My question is on Long Life Pennzoil. I know it's targeted at fleets and also used in gas/diesel engines. Is the 15W40 a great product in Summer for high mileage engines with varied oil burning. Is the 0W30 a good option for our MN Winters?