1991 buick regal 3.8 engine replace transmission fluid

I'm not sure I am following your problem.
A transmission holds 10-15 quarts including the torque converter. When you drain the fluid you are changing about 4 quarts of the full amount.
Once you fill the transmission to the full mark on the dipstick, you should not be adding more fluid unless there is a leak. Or if the vac modulator is damaged and allowing fluid to be pulled into the engine. The fluid is checked with the engine running in park.

Depends on your engine.

1980 JEEP CJ-7 2.5L 4-cyl Engine Code [B]
CAPACITIES
Engine, GM without filter..........2.4 quarts[1]
Wix Filter ........ 51040
Cooling System, Initial Fill..........8.0 quarts
Automatic Transmission, A904, 30RH Initial Fill..........4.0 quarts[2]
Automatic Transmission, A999, 32RH Initial Fill..........4.0 quarts[2]
Automatic Transmission, Total Fill
3 speed A999, 32RH..........8.4 quarts
3 speed A904, 30RH..........7.0 quarts
Manual Transmission, 4-SPD, SR-4..........3.0 pints
Manual Transmission, 4-SPD, T176..........3.6 pints
Differential, Front..........2.5 pints[3]
Differential, Rear..........4.9 pints
Transfer Case,..........4.0 pints

1. Add extra oil when replacing filter. After refill check oil level.
2. With engine automatic transmission operating temperature, shift through all gears.
Check fluid level in NEUTRAL and add fluid as needed.
3. 1984-1992 Models with command-Track, add 5 oz of 75W-90 GL-5 to shift motor housing opening.

TORQUES
Oil Drain Plug.....25 ft-lbs
Manual Transmission T176
Fill Plug.....15 ft-lbs
Drain Plug.....15 ft-lbs
Manual Transmission SR4
Fill Plug.....20 ft-lbs

1980 JEEP CJ-7 4.2L 6-cyl Engine Code [C]
CAPACITIES
Engine, without filter..........5.0 quarts[1]
Wix Filter..... 51522
Cooling System, Initial Fill..........11.0 quarts
Automatic Transmission, A904, 30RH Initial Fill..........4.0 quarts[2]
Automatic Transmission, A999, 32RH Initial Fill..........4.0 quarts[2]
Automatic Transmission, Total Fill
3 speed A999, 32RH..........8.4 quarts
3 speed A904, 30RH..........7.0 quarts
Manual Transmission, 4-SPD, SR-4..........3.0 pints
Manual Transmission, 4-SPD, T176..........3.6 pints
Differential, Front..........2.5 pints[3]
Differential, Rear..........4.9 pints
Transfer Case,..........4.0 pints

1. Add extra oil when replacing filter. After refill check oil level.
2. With engine automatic transmission operating temperature, shift through all gears.
Check fluid level in NEUTRAL and add fluid as needed.
3. 1984-1992 Models with command-Track, add 5 oz of 75W-90 GL-5 to shift motor housing opening.

TORQUES
Oil Drain Plug.....30 ft-lbs
Manual Transmission T176
Fill Plug.....15 ft-lbs
Drain Plug.....15 ft-lbs
Manual Transmission SR4
Fill Plug.....20 ft-lbs

1980 JEEP CJ-7 5.0L 8-cyl Engine Code [H]
CAPACITIES
Engine, without filter..........4.0 quarts[1]
Wix Filter..... 51258
Cooling System, Initial Fill..........13.0 quarts
Automatic Transmission, A999, 32RH Initial Fill..........4.0 quarts[2]
Automatic Transmission, A904, 30RH Initial Fill..........4.0 quarts[2]
Automatic Transmission, Total Fill
3 speed A904, 30RH..........7.0 quarts
3 speed A999, 32RH..........8.4 quarts
Manual Transmission, 4-SPD, SR-4..........3.0 pints
Manual Transmission, 4-SPD, T176..........3.6 pints
Differential, Front..........2.5 pints[3]
Differential, Rear..........4.9 pints
Transfer Case,..........4.0 pints

1. Add extra oil when replacing filter. After refill check oil level.
2. With engine automatic transmission operating temperature, shift through all gears.
Check fluid level in NEUTRAL and add fluid as needed.
3. 1984-1992 Models with command-Track, add 5 oz of 75W-90 GL-5 to shift motor housing opening.

TORQUES
Manual Transmission T176
Fill Plug.....15 ft-lbs
Drain Plug.....15 ft-lbs
Manual Transmission SR4
Fill Plug.....20 ft-lbs

Oilman

1991 GEO STORM 1.6L 4-cyl Engine Code 5 DOHCCAPACITIES
Engine, with filter.......... 3.2 quarts
Cooling System, W/ MT Initial Fill.......... 7.4 quarts
Cooling System, W/ AT Initial Fill.......... 8.0 quarts
Automatic Transmission, Initial Fill........ 4.3 quarts [1]
Automatic Transmission, Total Fill......... 7.0 quarts
Manual Transmission, ..........4.0 pints[1] With ENG at operating temperature, shift through all gears.
Check fluid level in PARK and add fluid as needed.1991 GEO STORM 1.6L 4-cyl Engine Code 6 SOHC
1992 GEO STORM 1.8L 4-cyl Engine Code 8 DOHCCAPACITIES
Engine, with filter.......... 4.0 quarts
Cooling System, W/ AT Initial Fill.......... 8.0 quarts
Cooling System, W MT Initial Fill........... 7.4 quarts
Automatic Transmission, Initial Fill........ 4.3 quarts [1]
Automatic Transmission, Total Fill......... 7.0 quarts
Manual Transmission, .......... 4.0 pints[1] With ENG at operating temperature, shift through all gears.
Check fluid level in PARK and add fluid as needed.

Your radiator is connected to the transmisiom to cool the transmission. the tank in the radiator has ruptured and transferring fluid to where it should not be. solution replace radiator. This will transfer trans fluid to cooling system and vice versa. I can not see the trans oil ending up in the engine oil sump for any reason?

Check your transmission line's, also look under your car if leaking between engine and transmission more then likely it's going to be your front transmission pump seal, transmission will have to come out to replace front seal.Don't let it run low on transmission fluid or you will have to replace or overhaul your transmission, not cheap.

1-If you open your oil cap and seeing a milky stuff at the inside cap, then there is a leak in head gasket. coolant mixed with oil through head gasket leak then vaporize leaving the milky stuff at your cap. 2-If you don't see it then there is possible transmission get into water. When you are running, the pressure from transmission is higher than coolant pressure so it leaks into your coolant thru transmission cooling coil in the radiator. 3-Need to address this as soon as possible since chance of car not running in the middle of a trip is high also consequences of problems are more costly. Good luck.

Four quarts if you drained it to change your filter.

CHECK TO SEE IF YOUR TRANSMISSION PAN GASKET IS LEAKING/IF NOT CHECK ALL HOSES AND LINES/IF NOT REPLACE YOUR REAR MAIN SEAL.

I am assuming you have the 200 4R, I just replaced my tranny fluid on my 87 GN, took about 6.4 quarts. I also have an external tranny cooler and let the tranny drain for about a week.

I would start with 4 quarts and start her up, dont drive anywhere. Keep adding and checking while the car warms up. Every now and then get in and shift through the gears, pausing in each one a few times, ALL GEARS. When the fluid level refisters on the dipstick, take the car around the block slowly at first then fast enough to shift into 2nd, depending on factors 3rd or 4th. Head home and leave engine running, check fluid again and adjust accordingly.

It is actually on the passengers side near the engine wall the pump and reservoir are made as one You will need a flash light follow the drive belt down past the alternator to the powersteering pump look for a black lid with a yellow steering wheel on top. The whole steering system takes only 3/4 quart of dextron automatic transmission fluid so do not over fill.