Transmission Fluid (ATF)

ATF works as a hydraulic fluid for shifting, a coolant and a lubricant. Different gearboxes need very specific fluids; the wrong one can cause shift problems. Some manufacturers call the fluid “lifetime”, but many specialists recommend changing it, especially under heavy use. The check and fill procedure often requires the fluid at a specific temperature.

Different transmissions need very different fluids. Automatic, CVT and dual-clutch transmissions each have their own specifications. Fluid condition says a lot about a transmission. Fresh automatic fluid is usually clear and often red, while old fluid turns darker and may smell burnt. Checking procedures differ: some gearboxes have a dipstick, but many must be checked at a fill plug at a set fluid temperature with the engine running, which is a job for a workshop.

A pump driven by the engine circulates fluid through the valve body, clutches and a cooler. The fluid creates hydraulic pressure to engage clutches, lubricates gears and bearings and carries heat to a cooler.

Low, old or burnt fluid causes slipping, harsh shifts and overheating. Dark fluid with a burnt smell often signals internal wear. Old or low fluid can cause slipping, harsh shifts and overheating. Some transmissions are called "sealed for life", but many manufacturers still recommend fluid changes under heavy use.