Originally Posted By: PimTac
The only times I question the oil spec from the manufacturer is when it's a engine that gets new oil specifications but it's the same engine as before.
For example, the Mitsubishi 6B31. The original requirement was 5w30, then shortly thereafter it was changed to 5w20. A few years ago the spec changed once again to 0w20. I cannot find any evidence that there were changes to the engine such as newer rings etc. Now if I owned a vehicle with that engine I would run 0w20 as long as there were no issues like consumption. But the question stays in the back of my head.
That was the case with my 08 Liberty, the engine ran on 5w30 for years with no changes to key components, then they changed the oil spec to 5W20. I ran that for a few years and decided to change my stable over to 5W30. My Pentastar engine was originally spec'd for 5W30, then 5W20 only. My owners manual gives me an option to run 5W20 or 5W30. I use 5W30.