I use to run 15w-40, but made the change to 5w-40 this past winter. That depends a lot on where you live, if you are in a hotter climate, 15w-40 may be better for you, although our 5w-40 provides great heat AND cold protection. Being in Canada, I would recommend 5w-40 all year round. That way you get the cold flow properties of the 5w at start up, and you can still run it year round....
10 qyarts equals 9.45 liters.