1994 Saab 900S 2.3L naturally aspirated with 58k miles. I have noticed that my engine is much quieter and seems to run very smooth. I also had a slight leak before when I was using havoline 5w30 full synthetic and with GC there is no more leak. It completely dryed up and is still dry. I have had the GC in now for only around 500 miles. Overall, the car seems pretty happy with this stuff. Here in Northern Maine the weather is definitely cold. Every morning it's usually around 0F this time of the year. The car turns over really easy and always starts. Those are the good things. Now for the not so good. I have noticed about a 2 mpg drop in my fuel on GC. I hope this gets better but its not enough of a drop to make me not use it.