Traditionally , Mobil 1 and Pennzoil Platinum headed the list of synthetics known to keep engines clean while lower tier oils (i.e. Quaker State , Castrol , Havoline , Valvoline , etc.) were not especially noted for keeping engines as clean as M1 and PPPP ... With so many synthetic oils now meeting the D1 / Gen 2 specs , would it be safe to say that the delta difference in engine cleaning ability of oils meeting the D1 / Gen 2 specs has closed considerably ? In other words , a D1 / Gen 2 rated oil with a decent oil filter run at a reasonable OCI in an otherwise good operating condition engine are going to clean about the same ? M1 and Penzoil Platinum may still hold a cleaning edge - but not nearly as great as before ... Your thoughts ?