Lubricating oil compositions with enhanced piston cleanliness

A method for improving the piston cleanliness of an internal combustion engine, the method comprising operating the internal combustion engine with a lubricating oil composition comprising:

• (a) from about 50 to about 65 wt. %, based on the total weight of the lubricating oil composition, of a first base oil component having a Kv at 100° C. of about 3.5 to about 4.5 cSt;
• (b) from about 10 to about 30 wt. %, based on the total weight of the lubricating oil composition, of a second base oil component having a Kv at 100° C. of about 5.5 to about 6.5 cSt;
• (c) about 1.5 wt. % to about 10 wt. %, based on the total weight of the lubricating oil composition, of at least one Mannich reaction product prepared by the condensation of a polyisobutyl-substituted hydroxyaromatic compound, wherein the polyisobutyl group is derived from polyisobutene containing at least about 70 wt. % methylvinylidene isomer and has a number average molecular weight of from about 400 to about 2,500, an aldehyde, an amino acid or ester derivative thereof, and an alkali metal base;
• and
• (d) at least one ashless dispersant other than component (c);
• wherein the lubricating oil composition has a sulfur content of less than or equal to about 0.30 wt. %, a phosphorus content of less than or equal to about 0.09 wt. %, and a sulfated ash content of less than or equal to about 1.60 wt. % as determined by ASTM D 874, based on the total weight of the lubricating oil composition;
• and further wherein the lubricating oil composition is a multigrade lubricating oil composition meeting the specifications for SAE J300 revised November 2007 requirements for a 0W-X multigrade engine oil, wherein X is 20, 30, 40, 50, or 60;
• with the proviso that when the lubricating oil composition has a sulfated ash content of less than or equal to 0.60 wt. %, based on the total weight the lubricating oil composition, the Mannich reaction product is present in at least about 3.0 wt. %, based on the total weight of the lubricating oil composition.