I have used gold GC for about 2500 miles in our 1999 Forester and 2002 M-B C230K. In the Subaru I noticed no change in mpg and maybe a little quieter compared to 5W-30 M1. In the M-B (2.3 liter 4 cyl with supercharger) there was no mpg change compared to M1 0W-40 or LDX 5W-40. However, after 48 hours of sitting, there is more engine noise at startup for a few seconds. I think it may be the cam chain tensioner losing pressure. It has been very hot in Missouri so the comparison may not be accurate.