What is the reason behind this?

[Blu_Ray_UK2007]

Greetings everyone, The gearbox filter and related components came today, bringing me closer to cleansing the fluid.
Due to the car's inactivity for one to two weeks, the gearbox fluid has depleted to the extent of indicating an excess or overfill condition.
Why not drain it now to extract the most of the fluid (I would just replace what is removed) instead of running it to warm it up before to the drain, which would provide a lesser amount?
reflections

[ChatMaven]

Valid observation. Particularly considering that the sump will be extracted and sanitised.

I hypothesise that a drain after an extensive run will extract a greater quantity of sludge and debris, supposing that, when cold, part of it may settle in different locations beyond the sump.

[ianwh4]

Remember to clean the magnet in the sump pan.

[Blu_Ray_UK2007]

I also considered it, but I fail to see why the sludge would not have settled in the pan after the previous operation. If it were to get stuck, it would have done so anyway.

[Screwdriver_1]

Indeed, you may extract fluid from the sump, perhaps yielding just over 4 litres. Subsequently, replenish with 4 litres, then either take a drive or use the engine before draining again. Finally, remove the sump and replace the filter as you would during a gearbox service.

[Blu_Ray_UK2007]

Thank you. I considered restoring the drained fluid and then replacing the filter and cleaning after the operation. However, I considered it prudent to eliminate the existing sludge from the pan first to prevent its circulation or re-entrance. I must simultaneously replace the filter.

[Screwdriver_1]

Undoubtedly, any further efforts you do will enhance the situation.
I replace the sump ATF annually (£28) by extracting it via the dipstick tube and replenishing it in the same manner. I subsequently replace the filter every 30,000 to 35,000 miles.

[developer]

Automatic gearboxes do not contain muck if coolant has not leaked from the radiator into them.

Nearly all advice on gearbox service (draining, flushing, avoiding overfilling, etc.) is based on misconceptions.

The oil remains viable provided the vehicle is not left to deteriorate in a damp environment for years, and the filter remains unobstructed if the clutch packs are not disintegrating due to damage.

A well functioning gearbox may go 200,000 miles on the original fluid without issues.