The green coolant is an inorganic additive technology (IAT). With this type of coolant, phosphates along with silicates are added to ethylene glycol. This helps to protect the metals that are in the vehicle’s cooling systems from becoming corroded. There are some IAT coolants that use propylene glycol instead of ethylene glycol.
The orange coolants are organic acid technologies (OAT). These were created for newer vehicles that had more nylon and aluminum parts in them. OAT coolants use organic acids in order to prevent corrosion.
Some people believe that they can mix the twot. This is a mistake and can lead to expensive repairs. The two coolants should never be mixed together as they do not react well. When mixed together they can form a thick, jelly-like substance that can completely stop all coolant flow which can lead to overheating.