Is a cetane improver required? I have read so much about this topic I am pretty much befuddled by it all. Some point to low cetane levels in ULSD, I have been told that Ford recommends a certain cetane level that is higher than that found in most USLD. I read that cetane levels are different based on whether you buy fuel that meets Canadian versus US specs.

What does GM say? After all they warrant the engine.