As I recall, I used QS in my first car, the '75 Ford Maverick with the larger (ha!) six-cyl. engine. I changed every 3500 miles or so, and drove the car from 1976 to 1981 without any issues. I guess I was using the detergent oil!
I'm using the QS Defy in the Buick now, and it may have slowed the oil consumption. I'm at 2500 miles on the fill, and the oil is still within the cross-hatched area on the dipstick. On most of the non-HM oils I've tried since I've had the car, I've had to add a quart within that time -- and Castrol Edge gulped a quart in 1200 miles.
I'm using the QS Defy in the Buick now, and it may have slowed the oil consumption. I'm at 2500 miles on the fill, and the oil is still within the cross-hatched area on the dipstick. On most of the non-HM oils I've tried since I've had the car, I've had to add a quart within that time -- and Castrol Edge gulped a quart in 1200 miles.