Red Line 30505 D4 Full Synthetic ATF - 1 Gallon

Red Line 30505 is the one-gallon jug of their D4 full synthetic automatic transmission fluid. It is a polyol ester based ATF built to cover the Dexron III, Dexron II, Mercon and Mercon V service fills, which makes it the jug most shops keep on the shelf for mixed domestic and import work instead of stocking four separate part numbers.

Red Line lists D4 for Toyota Type T-III and T-IV, Honda ATF-Z1, Nissan Matic D, J and K, Diamond SP-II and SP-III, Mazda ATF M-V, and most BMW and Audi/VW automatics. It is also rated for manual transmissions and transaxles - T-5, T-45, T-56 and late-model BMW gearboxes - where it gives GL-4 level gear protection, and it can be used as a power steering fluid where an ATF is specified.

Where it earns its keep on the bench is heat. A synthetic ester base holds its film and its viscosity at converter-outlet temperatures that cook a conventional fluid, so the friction material is not fighting a fluid that has already thinned out and started to varnish the valve body. The same balanced friction modification is what keeps cold-morning shifts from banging in a unit that is otherwise healthy. If you are refilling after a rebuild or a pan and filter service, check the OE fill spec first - this covers the Dexron/Mercon family and the imports listed above, but it is not a substitute for a fluid with its own unique spec such as ATF+4, Mercon LV, Dexron VI low-viscosity, or a fluid written for a continuously variable belt drive.

One gallon is 128 fluid ounces, roughly four quarts, which handles a typical pan-drop-and-filter service on most passenger car automatics. A full rebuild or a cooler-line flush will take more than one jug.