Ok. I've used Mobil 1 oils since 1978 and have never found an engine with any visible sludge or varnish at 10K OCI. Mobil 1 oils have an outstanding record here for keeping engines clean. The tri synthetic era was a long time ago, but I have found the Mobil 1 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 Mobil 1 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 Mobil 1 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 Mobil 1 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.
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