GMC Repair: mixing dexcool and green coolant, ethylene glycol, gm tech

Question
What can happen if these two coolants are mixed.I noticed in my 97 Sonoma there is green in the radiator and dexcool in the reservoir.I checked both fluids with a tester and both tested good.You guys are great!THANKS

Answer
Hi Nathan
Lets see if I can answer this and not offend anyone.
Being a long time GM tech, I would say to flush your system thourghly, flush the resivoir jug and refill with the proper coolant (dexcool in your case). According to trade publications I have read, mixing them really does not create any serious problems, OTHER than the coolant looses it's extended life properties. So it will need to be treated as conventional "green" coolant as far as service intervals are concerned. Now another "kink" to this is some Dexcool used in Asian vehicles is green in color. Dexcool is an OAT (Organic Acid Technology). Now Ford and Chrysler (and some European) Models now use G-05 Antifreeze which is usually Yellow in color. G-05 is a Hybrid Organic Acid Technology (HOAT). I have also seen G-05 that is Red in color.  So going by color only is not always a true test. So all this being said, My advise is TRY not to mix them if possible. Use what originally came in vehicle, again if possible. If mixed, my advise would be to get the vehicle professionally flushed, including the resivoir jug. Then refill with proper coolant that was original to vehicle. Again, though what I have read, it really will not hurt any system, other than having to treat the mixed coolant as regular "Green" Ethylene Glycol antifreeze.
If I offended any other Mechanics or Technicians with this, I apologize. I am JUST giving advise.