Over a year ago, similar thread, I posted my cocktail. Was mostly blown off, but now that I have at least one backer on this thread who will agree that sheering of Mobil 1 is not an issue and that viscosity improvers aren't that bad if you change your oil every 3k...
My recipe, needless to say only Mobil 1:
2.5 quarts 15W-50
3.0 quarts 0W-30
Net result:
6W-38 (roughly)
This was because I couldn't find 0W-40 in the states. Once they start selling it in Cleveland I'll switch.
Look at the clearances post, our engines are not that much tighter than what was made years ago. Yet back then, not as concerned about EPA gas mileage, a brand new engine would get 10W-30 dino. Now we're feeding 5W-30, 0W-30, 5W-20 synth?
For best engine life, your cold number should be between 0 & 10 depending on the season and where you are in North America.
Your operating temp number should be around 40 in my humble opinion. I don't have the numbers in front of me, but my gut says 40 synth flows just as well as 30 dino (anyone with DATA to double check?)... and it protects many times over. See BMW data. So it's not like the engine is circulating less oil when I use a 40ish synth compared to the 30 dino they put it at the factory, and all these years at the dealers.
Know I'll get flamed for this somehow.
Brian Dors
99 SVT