That is because you can't access what is in the torque converter unless the car is on and the trans pump is pumping fluid or other device.
When you drain, all you can get out is what is in the pan. Which is why to do a good clean change, you need to drain and fill at least a couple times, in which you drive around for a bit in between.
When you drain, all you can get out is what is in the pan. Which is why to do a good clean change, you need to drain and fill at least a couple times, in which you drive around for a bit in between.
