Both are etheleyn glycol based. The difference is in the additive package. DexCool uses organic acid technology (OAT). Green coolant uses phosphates and / or silicates to provide anti corosion protection. Both are actually somewhat abrasive and will eventually destroy water pump bearings and seals. Silicates also will eventually fall out of suspension leaving the system unprotected. Phosphates will combine with hard water to leave deposites. Europe has more hard water than the US, so european automakers usually specify coolant that is phosphate free. Green coolant will aslo in time become acidic which is harmful to all of the cooling system including seals, gaskets, and metals. OAT has more resistance to becoming acidic, does not fall out of suspension, is not sensitive to hard water, and is not abrasive to seals and water pump bearings.
That is what I have learned from research. There is a lot of controversy about the compatibility of orange and green coolant. It is better that they are not mixed. Some claim that the two will react and cause damage, while Texaco claims that all that happens is that you will no longer have the long life property.
DexCool works for me. I have been in the habit of changing coolant once a year so green coolant might be OK, but I have used DexCool on the SVT since it was a year old (it is not 4 1/2). I use DexCool on the car it replaced since shortly after DexCool was introduced. Radiators do not gunk up, coolant doesn't turn acidic and rot out cooling system parts, water pumps last longer, hoses do not get crusty and last longer.
Texaco used to have an abundance of information on their web site, but the last time I looked most of the information was gone. Fortunately I did print it for future reference.
