Description Mobil Delvac 1™ ATF 668 is a fully synthetic transmission fluid recommended by Allison Transmission, Inc. that is approved against the Allison TES 668® specification, and is backwards compatible for applications recommending Allison TES 295®.  The fluid is designed to meet the demanding requirements of modern heavy duty automatic transmissions. The synthetic base oil composition enables excellent performance even in some of the harshest of operating conditions. It offers outstanding gear shifting and power transfer performance. Versus conventional ATF fluids, the inherently high viscosity index and stability of  Mobil Delvac 1™ ATF 668 helps protects against thermal breakdown at high operating temperatures, while still providing outstanding performance at sub-zero temperatures.