Automotive engine coolant composition, automotive engine concentrated coolant composition, and method of operating internal combustion engine

An automotive engine coolant composition comprising:

• a sole surfactant as a viscosity index improver;
• a rubber swelling inhibitor;
• and
• a base, wherein
• the rubber swelling inhibitor is at least one selected from a compound expressed by a formula (1):
• in the formula, R1 is hydrogen, a methyl group, or an ethyl group, and a compound expressed by a formula (2):
• in the formula, R2 is hydrogen, a methyl group, or an ethyl group,
• the base includes at least water or an alcohol selected from the group consisting of a monohydric alcohol, a dihydric alcohol, a trihydric alcohol, and a glycol monoalkyl ether,
• a kinematic viscosity is 8.5 mm2/s or more at 25° C.,
• the sole surfactant is an anionic surfactant selected from the group consisting of a polyoxyethylene alkyl ether sulfuric acid ester salt, an alkyl phosphoric acid ester salt, and a polyoxyethylene alkyl ether phosphoric acid ester salt, and
• a content of the rubber swelling inhibitor is 0.03 parts by mass or more and 0.9 parts by mass or less with respect to 100 parts by mass of the coolant composition.