Lubricant oil composition and lubrication method

A lubricating oil composition, comprising:

• a base oil (A) comprising a mineral and a synthetic oil, wherein the synthetic oil comprises at least one ester oil and optionally at least one poly-α-olefin;
• an olefin polymer (B), which is an ethylene-propylene copolymer having a number average molecular weight of 1,500 or more and 7,000 or less;
• a sulfur compound (C) represented by formula (3):
• R1—Sm1 (1)
• wherein R1 represents a divalent hydrocarbon group, m1 represents an integer of 4, n1 represents an integer of 10 or less, p represents an integer of 1 or more and 4 or less, and R3 and R4 each represent a monovalent hydrocarbon group;
• at least one thiadiazole compound (D1);
• and
• optionally, polymethacrylate,
• wherein:
• the content of the base oil (A) based on the total amount of the composition is at least 80% by mass,
• the content of the synthetic oil relative to the base oil (A) ranges from 5.96% by mass to 20% by mass, with the balance of the base oil (A) being the mineral oil,
• the content of the at least one poly-α-olefin based on the total amount of the composition is 9% by mass or less,
• the content of the olefin polymer (B) based on the total amount of the composition ranges from 3% by mass or to 8% by mass,
• the content of the sulfur compound (C) based on the total amount of the composition ranges from 0.2% by mass to 1.5% by mass,
• the content of the thiadiazole compound (D1) based on the total amount of the composition ranges from 1.5% by mass to 4.5% by mass,
• the content of polymethacrylate based on the total amount of the composition is 5% by mass or less, and
• the content of all sulfur atoms based on the total amount of the composition ranges from 1.59% by mass to 2.5% by mass.