Red Line’s most popular and versatile ATF, D4 is suitable for use where Dexron III, Dexron II, or Mercon fluids are recommended. D4 ATF is a fully-synthetic product designed to satisfy the improved low-temperature requirements which will be in the new Dexron IV specification, and the improved shear-stability requirements which will be part of the new Mercon specifications.

D4 ATF also provides a GL-4 level of gear protection, making it a superior product for transmissions and transaxles like the Corvette's T-56. The balanced frictional characteristics provide smooth and consistent shifts for extended drain intervals. The superior stability compared to petroleum ATFs allows high-temperature operation without varnishing valves and clutches which leads to transmission failure. It’s stability allows high-temperature operation without varnishing valves and clutches. Also provides improved shifting in cold weather.