Originally Posted By: Char Baby
I am currently using DEFY 5w30 in my older Firebird FORMULA V8-4bbl. And it has made the engine the smoothes/quietest even compared to MaxLife or Castrol HM/Castrol Start-Up. A little too quiet for this particular car(lost some rumble) and not quite to my liking for this particular car(although, I don't hate it and I may stay with it).
But, I love the smooth/quiet in our other cars.
ATMOF, I am using QS oils(QSUD, QSGB, DEFY) in all of my cars right now and it certainly has made my engines as smooth/quiet as any of the best oils that I have tried. Or I should say...certain oils make engines quiet compared to others and QS oil is one of them!
Not surprised at all, I think it's the boron heavy add packs. Every boron heavy oil I've tried so far has resulted in quiet running. I suspect this is one of the reasons Hyundai/KIA have been using/recommending QSGB for a number of years, they've received some criticism for engine noise and the boron heavy QSGB does a good job of quieting those engines down.