Transmission fluid lubricates and cools the gearbox and (on automatics) operates the hydraulic systems that control gear changes. Like engine oil, it degrades over time and needs periodic replacement, though this is often overlooked because it is not part of a standard service in many garages.
Manual gearbox oil
Manual gearboxes use gear oil (sometimes called transmission fluid) to lubricate the gears, bearings and synchromesh components. In many modern manual gearboxes this is listed as a sealed-for-life fill and the manufacturer does not specify a change interval. In practice, after high mileages or in performance applications, a change can improve gear quality and reduce wear. If you notice stiff or crunching gear changes on a higher-mileage manual car, a gearbox oil change is worth considering.
Automatic gearbox fluid
Automatic transmissions are more sensitive to fluid condition than manuals. The fluid in an automatic gearbox also acts as a hydraulic fluid for the transmission control system. Degraded fluid causes rough, delayed or shuddering gear changes and can cause serious and expensive damage to the transmission if neglected. Most manufacturers recommend a change between 40,000 and 80,000 miles, though some specify sealed-for-life (which many mechanics and owners dispute in practice).
CVT and DSG gearboxes
Continuously variable transmissions (CVT) and dual-clutch (DSG) gearboxes use specialist fluids with their own change intervals. Using the wrong fluid type in these units can cause immediate damage. Always use manufacturer-specified fluid.
Signs your transmission fluid may need changing
- Rough, delayed or shuddering gear changes.
- Slipping between gears.
- A burnt smell from the transmission area.
- Fluid that has turned dark brown or black (check the level using the dipstick if your transmission has one).
To discuss gearbox fluid changes or any transmission concerns, call Steins Garage on 0131 554 3423 or contact us here.