The mix: 3.5qts 15w-50 Mobil 1 EP with 3.5qts Mobil dino 5000mi 10w-40 I’ve been blending for 11k miles now on my s52 powered 97’ BMW M3 with 93k on the clock with no reports of oil loss/consumption or potential engine damage. Before this, the changes were anywhere from 5-7k miles on anything from 10w-30 to 20w-50 or 15w-50 by the owners. The first two changes were M1 15w-50 and Valvoline high mileage 10w-40. The reasoning behind the blend is a follows – These aren’t facts, just stuff I’ve been able to put together after reading the forums so use this guide loosely - I’m no chemist by any means, so I could be completely wrong about my assumptions below: Daily drive 8mi round trip commute in stop/go Atlanta traffic – Synthetic protection wanted 93k mile old motor – let’s remove some buildup and clean passages – Extended performance/5000mi includes detergents/cleaners package Short oil change intervals – Mixing dino with Syn have an economic $ balance and the short changes are to flush out deposits/4000mi old oil. I track my car monthly at Barber, Road Atlanta, etc..- Syn protection and high heat resistance wanted and a reason why 15w-50 was picked as ½ of the blend. I like the 10w-40 for the “colder” mornings in the winter when it can get as low as 20 degrees (still “warm” for the Midwestern/northeastern people – I feel your pain – I’m from MN.) I open to suggestions, bashing, ridicule, etc. I want to really know if I doing something that can cause a problem. I’m going to pull a sample for a UOA from this most current batch (Has a 1000mi round trip to Indianapolis, 1 weekend at road Atlanta, and 2600mi of daily driving on it) Thanks for looking. Please share your opinion.