Prepare your semi truck to be Ready for the Road Ahead , with the Castrol Heavy Duty Multipurpose Automatic Transmission Fluid that provides enhanced transmission performance. Due to its high viscosity index, this replacement fluid is the ideal option to cool a transmission in high temperatures, while also lubricating, sealing, and protecting it. Blended with an advanced mixture to reduce how often the fluid needs to be checked or changed. FleetPride is your First Click in Heavy Duty .