At the first oil change I used Castrol (dino) but have used Mobil-1 (5w30) ever since, with a 7,500-mile change interval. However, I am now considering going with Amsoil (oil and filter) and changing the oil once a year.
In my opinion, there is no advantage to using synthetic oil unless you change the oil at the maximum interval or live in Frozen Buns, Nunavut, Canada, and require a ridiculously low pour-point.
My Mo gets excellent mileage & has excellent power. I've used Synthetic oils in my cars, motorcycles, and lawnmowers since early 1980. Initially, I did it due to the research that NASA had invested into finding the lubricants that would be a part of the space program, requiriing the ability to hold up under extremes, both high & low. I started with a graphite by ARCO. Then went to Mobil synthetic, and eventually to the Castrol Syntex. I now use either Castrol or Mobil 100% synthetic, depending upon the sale price at the time.
As a former engine rebuilder, I can tell you in a few ways how to prove the value of synthetic. First, pull apart an engine with 85,000 miles that had the oil changed @ 3000 miles with regular motor oil, then pull apart a similar engine that used 6,000+ mile intervals using synthetic. The noticeable wear difference alone will convince you to never use anything else. You can generally even look through the Oil filler cap opening at the camshaft lobes, and notice the wear difference-and that's without a micrometer, it's that obvious.
Then there is the cleaner engine. When I used to pull the intake off of small block engines, there would be a thin coating covering large areas, resembling wax paper in the upper engine. This was caused by the ash, sulfer,and other components of oil as it detiorated and formed a semi-dry coating. Those of us who worked on engines frequently and saw this, nicknamed it, "crustacious manifestus".
I do agree that you should benefit from the longer service interval when using synthetic. It would be wasting a good product to change it at the 3000 mile intervals. Honda, Mitsubishi & other manufacturers require the 6,000 mile interval, and suggest that you don't change your filter each tiime. The used filter has better filtration capabilities than a new one does due to the trapped particles providing extra filtration capabilities. (Mitsubishi 3000 GT & Dodge Stealth, & others.) BMW has an even longer oil change limit.
I encourage the use, it will save oil changes, filters, improve mileage, reduce engine wear, and that all adds up to saving you money in the long run.
On the Murano I always used Mobil1 5W-30 with change intervals of 5,000 - 6,000 miles.
On the FX35, same engine as the Murano, I recently switched to Castrol Edge and now to Pennzoil Platinum. The change intervals - 6,000 miles. After 100,000 miles on the odo the FX engine could not be happier.
Oil change intervals - GM has OLM (Oil Life Monitor). If I followed it I would change oil in my CTS every 12,000 miles or so!
To begin with, I got a big kick out of CORIN's remark regarding synthetic and non sythetic where he says "a lot of good info and quite a few religious wars about the subject"
However there is still seems to be a lot of confusion out there and it likely will continue. Just a point of info, I NEVER used synthetic and my 1997 Max got to 280,000k and still wasnt hardly using any oil. I checked it very closely all the time and especially on our trips back and forth to Arizona from Canada and the oil useage was negligible.
I have always made a point however to change the oil AND FILTER on a fairly regular basis.
I never had any starting problems in cold weather. The filters were the regular dealer filters whatever they were.
So.........I will do a bit more research on it, and likely use the synthetic in the Murano, but you can see the non synthetic oil served me very well in the Max.
Something about the statement "The used filter has better filtration capabilities than a new one does due to the trapped particles providing extra filtration capabilities" makes me scratch my non technical head--you could go on the premise that if you really let your filter get dirty it would really be better for the vehicle, but hey why change it at all!!