Ok. I've used M1 oils since 1978 and have never found an engine with any visible sludge or varnish at 10K OCI. M1 oils have an outstanding record here for keeping engines clean. The tri synthetic era was a long time ago, but I have found the M1 oils in the last 20-25 years have once again kept my engines very clean even with high mileage engines like my present Ford Fusion with 333K, again with 10K OCIs. The so called vanilla M1 is still and outstanding product with OCIs good for 10K and beyond. Now with direct injection turbo engines I might drop back to 7-8K perhaps, but I have no need for turbos. I have talked to Mobil tech and they have tested turbo engines and they claim that M1 10k oil will actually surpass 10K by several K. So I just roll my eyes when threads present other oils clean up dirty engines that used M1 oils, especially with 5K OCIs which for most engines is a waste of oil and filters. This is my 07 Fusion at about 330K. Any discoloration is residual oil. and not varnish. Nothing was cleaned up.
View attachment 291579View attachment 291579