Need to know how many quarts of trans fluid do I need for a change on the 4l60 since I added a trans cooler.

Thanks in advance

 

I presume it's a stock cooler - and a LS1 Fbody?

If so, 5 quarts for pan type drain, or 10.8 quarts for complete overhaul (includes converter), then check level with dipstick when warm.

The quantities are taken from page 0-34 of the 2K GM service manual.