Opaque non-aqueous suspensions of nano-particles mixtures are difficult to analyse directly in terms of particle behaviour under shear conditions (flow). This work proposes a rheological characterisation of a nano-iron-carbide-rich solid phase dispersed in decalin. These suspensions have shown a non-Newtonian, shear thinning, no-thixotropic behaviour at three temperature levels and five concentration levels. Based on acoustic attenuation spectroscopy, it is concluded that the aggregation state of the suspension does not change with solids content. The relationship between viscosity, concentration and shear rate was modelled at three temperature levels using two phenomenological methods.