This 2021 BMW X3 came in for transmission fluid maintenance with nothing wrong with it — which is the best time to do it. Under the car, the transmission pan carries a green BMW sticker: “Warning — Lifetime oil.” The same sticker also prints the oil filling temperature, 104°F to 122°F. Both lines matter, and we explain why in our article on the “lifetime” transmission fluid myth.
Draining the “lifetime” fluid
The transmission in this X3 is the ZF 8-speed automatic. ZF, the company that builds it, publishes its own fluid and filter service recommendation for it, whatever the sticker says. Fluid in an automatic does more than lubricate: it is the hydraulic medium that applies the clutches, and it carries away heat. Over the years it breaks down and picks up wear material, and the filter slowly loads up.
The pan is the filter
On this transmission the filter is built into the plastic pan, so a proper service replaces the pan, the filter and the fluid together — a drain-and-fill alone leaves the old filter in place. With the pan off, the valve body is exposed: the block of passages and solenoids that the fluid flows through to shift the gears.
New pan in, filled to temperature
The new pan and filter went on and the transmission was refilled. This unit has no dipstick: the level is set at the fill plug, with the fluid at the temperature printed on the pan — 104°F to 122°F. Fill it cold and it ends up overfilled; fill it too hot and it ends up low. Either one causes its own problems, which is why the temperature is on the sticker in the first place.
What to take from this
“Lifetime” fluid usually means the lifetime of the warranty, not of the transmission. Changing the fluid and filter on a healthy transmission costs far less than repairing one that has been run on worn-out fluid. If your BMW, Audi, Jaguar, Land Rover or Ram has the ZF 8-speed and has never had the fluid changed, it is worth asking about. More on our transmission service and on how we look after the brand on our BMW service page.