Transmission Fluids Explained

Transmission fluid is used to protect and operate vehicle gearboxes. It plays a different role to engine oil and is specifically formulated for how transmissions function under load.

Both manual and automatic transmissions rely on the correct fluid to operate smoothly and reliably.

What transmission fluid does

Transmission fluid lubricates internal components, reduces wear, and helps control heat. In automatic transmissions, it also acts as a hydraulic fluid, enabling gear changes and torque transfer.

Without correct fluid performance, gear changes become harsh, delayed, or unreliable.

Automatic transmissions

Automatic transmissions rely heavily on fluid performance. The fluid must maintain precise friction characteristics to allow smooth gear changes.

It also transfers power through the torque converter and helps cool the transmission during operation.

Manual transmissions

Manual gearboxes use transmission oils designed to protect gears and bearings under load. These oils must balance protection with suitable friction properties for synchronisers.

Using the wrong fluid can cause poor gear engagement or increased wear.

Fluid specifications

Transmission fluids are highly specific. Many vehicles require fluids approved to exact manufacturer specifications.

Even fluids that appear similar can behave very differently in service, which is why specifications exist.

What transmission fluid is not

Transmission fluid is not interchangeable with engine oil. It is not a universal product and should not be selected based on viscosity alone.

Its purpose is to support gearbox operation, not engine lubrication.