My owners manual says "don't add any additives". An earlier poster said that his required D4985 and mine only required D3306 listed as corrosion additives. It's pretty clear that the specs have changed over the 23 years. Someone said that his recommended 60% coolant. Mine says "no more than...
my 1999 & 2000 JD 4400 & 4600 call for ASTM D3306 (JD H24C1). "Prestone GM" coolant says it meets the specs for D3306 & D4985. No more than 50/50 , no other additives, and add Distilled or deionized water.