according to my Dmax manufacturer's manual (which is different from dealer's PMS) every 40,000 km. puede rin every 30,000 km. just use the right classification of axle oil with proper selection of viscosity. if you are using FUEGO, it might be GL-5 class with SAE of 90 or 140. for my '94 model isuzu pick up, i use SHELL SPIRAX GL-5 with SAE of 140. The SAE 90 works in the MAXIMUM temp of 37 deg C ambient or surrounding temp...