As far as checking the ATF level, the fluid must be at operating temp: at least 20km / 12mi of driving.
For my 2000 GMC Sierra, with the motor idling and the truck on a LEVEL surface, slowly go through the range from Park to One and back to Park, letting it sit for about 5 secs in each range.
Then take out the stick and wipe it, put it back in, pull out and check the level.
This is per the Helm shop manual.
As far as cold weather use, the Brookfield viscosity has a limit of 100 Poise before shift solenoids/springs and the torque converter will fail.
Most conventional Dexron III ATF's reach 100 Poise at around -35 C.
If you operate HD Allison automatics, they REQUIRE a "preheat" in temps colder than -25 C / -13 F. The "preheat" means to use an electric pan heater or to run the motor in P (If equipped) or N for a minimum of 20 minutes.
They warn if you attempt range operation, as in driving off, you could cause transmission failure that would NOT be covered by warranty.
I've seen folks who have attempted to yank the selector into D at -40 and nothing happens. So they floor the pedal, somehow thinking that "helps." They grenade the torque convertor or main pump. I'd let it run 5 min minimum.
So I think it's important to use the correct ATF. If your car takes Dexron III, then in most parts of Canada and the Northern U.S. and Alaska, the regular Dexron III can not be used below -35 C.
FWIW Mobil 1 ATF, which is approved for Dexron III and Allison C4 spec, has a rated Brookfield of 51.5 Poise at -40. This is what I use in my automatics and very good operation, even at -42.
Jerry
