Viscosity measuring apparatus

A viscosity measuring apparatus mounted on a vehicle comprising an engine, a cylinder pressure sensor configured to detect cylinder pressure which is inner pressure of a cylinder of the engine, a fuel injection valve configured to supply fuel to the engine, and a temperature sensor configured to detect temperature of a coolant of the engine, said viscosity measuring apparatus comprising:

• an estimating device configured to calculate a cooling loss from a heating value of the cylinder based on the cylinder pressure detected by the cylinder pressure sensor and an input heating value of the cylinder, and to estimate viscosity of the coolant on the basis of a relation between the viscosity of the coolant and a cooling loss, which is led from an operation condition of the engine and the temperature of the coolant detected by said temperature sensor, and the calculated cooling loss.