Red Line MTL 75W80 GL-4 Manual Gear Oil Case of 12 Quarts

Red Line 50204 MTL is a 75W80 synthetic gear oil that meets GL-4 and is built for manual transmissions and transaxles with brass or bronze synchronizer rings. It is the fluid to use where a special synchromesh fluid is specified: Dodge and Jeep NV1500, NV3500, NV3550 and NV5600, Land Rover LT77S, BMW, Honda and Acura manual transaxles, Ford Focus, late-model Mini Cooper, and most Mitsubishi manual boxes.

The reason it matters is sulfur. A GL-5 hypoid oil carries reactive sulfur additives designed for a ring-and-pinion, and those additives corrode the yellow metal in a synchro ring. Run GL-5 in an NV3500 and the synchros glaze, then the box starts grinding into second and third when cold. MTL is GL-4, so the anti-wear package protects the gear teeth without eating the synchro cones.

Friction is the other half of it. Straight synthetic gear oils are often too slippery for a synchronizer to grab, which shows up as a long, floaty shift. MTL is friction-balanced so the ring bites and the lever drops into gear. The 75W80 viscosity also drags less on a cold morning than a 75W90, which is why a Honda or BMW transaxle shifts cleaner on it. Twelve quarts covers a fill on most boxes with spares on the shelf: an NV3500 takes about 4.3 quarts, an NV5600 about 9.5.