I want to be sure my Automatic Transmission Fluid Level is correct. If I drive the car a short time (about 15 minutes), the fluid level is at or just below the very bottom of the HOT range mark on the dip stick. A drive of 40 minutes puts the level in the middle of the HOT range. A 2 hour trip on a hot sunny day puts the level at the top or even a little past the upper mark on the HOT range. Too much fluid? Too little? I don't know.
perfect
It sounds like it’s at the correct level, but a lot of owner’s manuals mention the correct procedure to check the ATF level, for that vehicle. Glance through what yours says.
The ATF fluid level is very much dependent on the fluid temperature. So if you are not controlling the fluid temperature precisely enough while you are doing your checks, you are not even theoretically close to any precise ATF level measurements.
Normally, what matters is the normal-hot level, which on all cars I know has to be measured at + 80 degrees Centigrade. The ATF dipstick usually has special level markings (max-min) for such temperature, and even this temperature itself is written on some dipsticks. Some dipsticks also have level markings for 20 degrees Centigrade, but those are not so relevant: at any temperature other than + 80 degrees Centigrade, the ATF level just has to be somewhere on the dipstick - does not really matter where.
The check is done when your car is standing on a level surface, with engine running- You may also want to switch between different gears shortly before you do your measurements, but I am not sure if this is a must for all gearboxes or just for some of them.
Important is that you "catch" the correct temperature with, say, +- 1 degree precision. There are different ways of monitoring the ATF temperature - from reading indications smart gearboxes provide via diagnostic scanners to just measuring the ATF oil pan temperature with IR handheld measuring devices. But if you want an exact measurement / level setting, you have to make sure you do it at the prescribed temperature. Just "drive your car for 15 minutes" is not precise enough.
Most important of all is, that you generally set yout ATF level when hot, and not when cold - the ATF volume / level setting error would otherwise be dramatic.
But as long as you are setting it when hot, it actually makes little practical sense to be overly pedantic about the ATF level: in the automatic gearboxes I saw from the inside, +- 0,5 liter deviations do not do any harm at all - the gearboxes are made in such a way that they cannot even notice such difference. Otherwise they would not be able to properly work provided those huge ATF level fluctuations between cold and hot.
The car needs to be warmed up, parked on a level surface and idling in park. Pull the dipstick, wipe it clean, reinsert, pull it out again and read the level. This will give an accurate reading.
