It isn't gallons, it is litres or quarts.

If you use the cooler lines to drain it, you will have to be running the engine and have the transmission in gear to get everything out. You don't just need to get the fluid out of the cooler, you need to get the fluid out of the torque converter and that is why you would have to be running it. There is a risk of damage due to running the transmission without fluid.

The usual way to use the cooler lines is to connect a flush machine, which often applies pressure. The risk here is that high pressure flushing can dislodge sediment. You can use some flush machines without pressure, removing fluid and adding it at the same time. You need a lot of fluid in this case, but it is possible.

If you want to get more than 50% of the fluid out, the accepted method of doing that is to drain and refil the transmission several times. You get 50% out the first time, then 50% of the mix out the second time (leaving 25% old fluid) and so on.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
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2002 325xi 5 MT, Steel Grey
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