Engine lubricant composition

A method comprising:

• lubricating at least one mechanical part of an engine;
• and
• contacting the mechanical part with at least one lubricant composition comprising, with respect to the total mass of the lubricant composition:
• from 40 to 80% by mass of at least one base oil, from 1 to 15% by mass of at least one viscosity index improver polymer selected from styrene from styrene/olefin copolymers and polyacrylates, alone or in a mixture, and from 4 to 8% by mass of at least one polyalkylene glycol, which is a copolymer of butylene oxide and propylene oxide with the butylene oxide to propylene oxide mass ratio being a value of 1:1, the polyalkylene glycol having the general formula (A):
• wherein
• Y1 is hydrogen and Y2 is hydrogen, or an alkyl group having 1 to 30 carbon atoms;
• n represents an integer greater than or equal to 2;
• x represents one or more integers ranging from 1 to n;
• the R2x-1 and R2x groups are, independently of each other, hydrogen, or hydrocarbon radicals, comprising from 1 to 2 carbon atoms;
• and
• for at least one value of x, the sum of the numbers of carbon atoms in R2x-1 and R2x is equal to 2,
• the polyalkylene glycol having a kinematic viscosity at 100° C. measured according to the standard ASTM of 4 cSt and a molar mass measured according to the standard ASTM D4274 of 505 g/mol.

A method for improving engine cleanliness, without increasing the consumption of gasoline or diesel fuel, the method comprising:

• providing at least one polyalkylene glycol, which is a copolymer of butylene oxide and propylene oxide with the butylene oxide to propylene oxide mass ratio being a value of 1:1, the polyalkylene glycol having the general formula (A):
• wherein
• Y1 is hydrogen and Y2 is hydrogen, or an alkyl group having 1 to 30 carbon atoms;
• n represents an integer greater than or equal to 2;
• x represents one or more integers ranging from 1 to n;
• the R2x-1 and R2x groups are, independently of each other, hydrogen, or hydrocarbon radicals, comprising from 1 to 2 carbon atoms;
• for at least one value of x, the sum of the numbers of carbon atoms in R2x-1 and R2x is equal to 2,
• the polyalkylene glycol having a kinematic viscosity at 100° C. measured according to the standard ASTM D445 of 4 cSt and a molar mass measured according to the standard ASTM D4274 of 505 g/mol;
• adding from 4 to 8% by mass of the polyalkylene glycol of the general formula (A) in a lubricant composition which comprises from 40 to 80% by mass of at least one base oil and from 1 to 15% by mass of at least one viscosity index improver polymer selected from styrene/olefin copolymers and polyacrylates, alone or in a mixture, with respect to the total mass of the lubricant composition;
• and
• bringing into contact the lubricant composition obtained at the previous step with an engine.