[onewhippedpuppy]

Remember that the OEMs are financially incentivized to maximize their fleet wide MPG, which has led to the spec of increasingly thin motor oils. Similarly they are motivated for your car to get past the warranty period with minimal issues, but after that point they make money when your car breaks. So blindly trusting the OEM or dealership may not always be in your best interests.

A good example is my RX8. They went from recommending 5W-30 in the RX-7 to 5W-20 in the RX-8 to combat the rotary’s notoriously crappy MPG. But the rotary engine building industry unanimously recommends against using either, as rotary engines run hot and need an oil less prone to breaking down. Most rotary engine builders recommend something like 15W-50 and will void your warranty if you use 5W-20 per the book.