I had the Terrain 2011 for one year and 29k miles with the I-4 AWD
I now have the 2012 Terrain AWD with the V6..I have about 1300 on that.
I drive alot, I use it for work.. I went with the I4 at first for the MPG.. but I didnt get good MPG.. i was around 19-21 MPG on the I-4.. I think it had enough power, it just really gets loud when you give it the gas to get it to go..I had an I-4 in my last vehicle, 2006 HHR with the I-4 2.4L. I had no issues with that engine..so I thought i would be fine with the I-4 on the Terrain too.
now I was fine with it, I just felt like the Terrain, to me, being a heavier vehicle than my HHR, that the engine really worked hard...again, this is my opinion, and obviously my driving habits!
Now that I have the V6 and Im getting 18-19 MPG..(so not really seeing any change in MPG) and the engine is quiet, and has plenty of power..moves quick getting on freeways or passing...
I wish that I would have gotten the V6 in the first place with the 2011..
Also I changed the oil on the I-4 every 7k..my oil life at 1300 miles shows 78%..so we will see how the oil changes go..( no, I dont go by just the oil life monitor...)