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Purpose – The purpose of this paper is to experimentally investigate the effect of aluminium oxide (Al2O3) nanoparticles on gear oil (SAE EP 90) as a lubricant in heavy earth moving machinery (HEMM). Design/methodology/approach – Particle size distribution, viscosity, density, stability and other rheological properties have been measured. The variations in rheological properties with varying nanoparticle volume fraction and temperature have been investigated at atmospheric pressure over a temperature range of 15-40°C. Classical as well as modified Krieger – Dougherty models have been used for finding out viscosity variation and a new empirical model has been presented. Findings – Dynamic light scattering data confirm the presence of large agglomeration of about 5.5 times of primary nanoparticles in nanofluid. Nanofluid starts behaving as a non-Newtonian fluid with increasing nanoparticle volume fraction. Viscosity of nanofluid is enhanced by 1.7 times of base fluid with 2 per cent volume fraction of Al2O3 nanoparticles, while it significantly decreases with increase in temperature. The stability of nanofluid decreases with increase in nanoparticle volume fraction due to settling down of nanoparticles. It has also been observed that shear thinning increases with increasing nanoparticle volume fraction. Practical implications – It is expected that these findings will contribute towards the improvement in rheological and thermal properties of the conventional lubricants used in HEMM. The outcome may help the designers, researchers and manufacturers of the HEMM. Originality/value – Most of the previous research in this field is confined with base fluid as water, ethylene glycol, transformer oil, etc. Gear oil in HEMM performs under high mechanical and thermal load. The Al2O3/gear oil nanofluid is expected to have better cooling and lubrication properties.

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