I have a 99 f150 xl 4.2l 4x4. I just swapped my radiator and fixed the contamination, but my trans had got water in the lines. I am going to drop the pan and swap the filter. My question is how much fluid should I add back to the truck because the radiator they sold me that was in my truck was for a 5.4 L V8 and it was the same part that was in my truck. Since I have swapped the radiator and now I’m about to drop the oil pan how much transmission fluid should I be putting back in my truck? Mind you that as of right now it’s showing overfilled, so I have no number to base it on to put back in my truck.

 

Measure how much you take out and replace that amount.

 

The Owners Manual doesn't show a difference by radiator. Only by transmission.

Motorcraft
MERCONt
ATF
5-speed manual 4 3.5L (3.75 quarts)
Automatic-E4OD
(4x2)
15.0L (15.9 quarts)
Automatic-E4OD
(4x4)
15.5L (16.4 quarts)
Motorcraft
MERCONt
V ATF
Automatic-4R70W 13.1L (13.9 quarts)

 

Those are dry refill numbers it looks like to me
AutoZone can usually tell you how much fluid you need for a trans service
Start with 7 quarts and add more as necessary.