What is oil transmission?

Transmission oil is a motor oil specifically manufactured for transmissions and differentials in cars. Compared to engine oil it is of a higher viscosity which ensures good transfer and better protects the gears. This heavy oil can create viscous drag and lead to inefficiencies in operation.

Some modern automatic transmissions do not use such a heavy oil at all but lubricate with the lower viscosity hydraulic fluid, which is available at pressure within the automatic transmission.

Transmission oil is usually associated with a strong sulfur smell.