So how do you know if it is full now? What if it wasn’t full from the factory? That does happen more than you think.. What if you have a slow seep that you are unaware of??
You should always preform the proper fill process in order to confirm the correct level… Never Assume it was full before hand… You have a full level plug of some kind, somewhere on your transmission, use it with the proper procedure (temp etc etc) to confirm it is full… How often would you just drain the fluid out of older transmission with a drain plug for the pan, and just put back in what came out of it, if it had a dipstick??
Or just play Russian Roulette with your transmission… Your choice…
you are right. I always thought the factory could have put the wrong amount in but had to first make the assumption that the level was right. And if it was low, I would have had problems. and if it was leaking, I’d see it on the floor of my garage, around the trans pan or other. Never had a leak even after changing the filter/pan gasket. I always wanted to do the level check on the first try when the car was brand new but just drained it at 13K, measured and then refilled it. go to bobsoilguy and they have a discussion on ATF and expansion. I agree with one poster that when hot and then cooled, the fluid level doesn’t change much. I wish I checked this when in the lab but I’m retired now. I think that 4.3% expansion number is way off (on 7 qts volume, 4.3% is roughly 300 mls). And someone said if the volume is 1 quart high or low, you’d see issues. Somewhere close, no problems. I do hear your argument as I’m a scientist and we have to be precise beyond belief in the lab. But I think changing the fluid sooner than later is more critical than being off a little on the volume. TBH, I’d rather the trans drain 100% out and not have any fluid in the torque converter. This way, 7 qts drains, 7 qts goes in. No issues there but the transmissions aren’t designed that way. Have a good day and enjoy working on your car to keep it running in tip top shape.