D4 Automatic Transmission Fluid is a fully-synthetic product designed with superior low-temperature properties compared to a Dexron III fluid, and the improved shear-stability requirements which is part of the Mercon V specifications. D4 Automatic Transmission Fluid also provides a GL-4 level of gear protection, making it a superior product for transmissions and transaxles. The balanced frictional characteristics provides smooth and consistent shifts for extended drain intervals. The superior stability compared to petroleum Automatic Transmission Fluids allows high-temperature operation without varnishing valves and clutches which leads to transmission failure