My 2007 Dodge Ram 2500 w/ the 6.7L Cummins diesel has 86k miles on the original coolant. I should have changed it earlier, but you know how it is. In the near future I intend to r&r the thermostat and flush the cooling system with distilled water, and then replace enough of the water with coolant to make a good 50/50 mixture. I would like to use one of the Fleetguard coolants, either ES Compleat (blue) or ES Compleat OAT (red). I understand the blue variant is an HOAT coolant, which would be similar to the factory fill. However, would a true OAT coolant be superior to HOAT?