The traditional green antifreeze. Same thing I've been using for 56 years. I buy the pure stuff and dilute my own for our temperature zone. If you buy the 50/50, so called antifreeze coolant mix, your paying a high price for half a jug of water.<span style="color: #009900">(Not to confuse with the industrial grade</span> <span style="color: #009900">antifreeze/coolant)</span> designed for industrial engines. I change the coolant in my cars and trucks every two years. I take my old coolants and oils to a processing center. PJ