Transmission Fluid Change Question: Gen 2

I have watched numerous YouTube videos demonstrating how to change the transmission fluid on a Gen 2 Tundra.

For the life of me, I don't understand why it isn't a simple matter of replacing with new fluid the amount that was drained.

All the videos involve bringing the transmission up to operating temperature then adding fluid while the transmission is warm and the engine is running.

If I were to drain slightly more than 3 liters of fluid from the transmission after it has cooled to room temperature, why wouldn't I just add that same amount of new fluid if it also is at room temperature.

I know there must be a reason this isn't correct, otherwise all these videos wouldn't be showing a harder way of doing it; I just don't understand what that reason is.

Thanks.

 

Because they can't expect people to understand expansion, or to see a slow leak, and I think it is their way of not owning a factory (or other tech's) failure.

I believe their instructions are meant to always reset the known, validated baseline.

 

Lots of people do what you're saying OP, but in the event your transmission has the wrong fluid level to begin with then you're still still at the wrong level. Personally, if I'm gonna go to the effort to check the level then I'm going to do an entire fluid flush so I get all new fluid and the right level, instead of replacing a small batch of old fluid.

 

My 2008 has 215k miles on it, always removed 3 qt and pumped in 3 qt, i drain and refilled 3 times, after a few short runs. Done this every 30k miles since new.

 

my simpleton method:

drain whatever comes out...usually 4-ish qts...measure it.

then refill with 5 qts

warm it up in park...open the check plug till it dribbles.

bam, you be done.