Just bought a used 2005 Malibu Maxx 3.5 liter V6 with now 87,000 miles on it, drove it from Ky to my new home here in Colorado. The dealership changed the oil with what I assume is Valvoline conventional. What would be a good oil for this car and the upcoming Colorado winter? I am thinking QS Defy (which I used it my old car), Valvoline Synthetic Blend, or Pennzoil Gold Syn Blend. So far I do not think there is any oil leaks, and with the harsh winter I was wanting to use a syn blend...