I have limited experience with aluminum alloys so I am not sure of the reaction products or the exact corrosion mechanism in this case. However, most corrosion caused by ethylene glycol is related to its decomposition to organic acids (such as glycolic acid) especially under elevated temperatures. The corrosion of aluminum alloy in the presence of ethylene glycol is most likely a result of acidic attack by these acids. It is known that impurities often found in ethylene glycol/water mixtures, such as ferric, copper, and chloride ions, can accelerate this corrosion. Corrosion problems with ethylene glycol/water mixtures can be minimized or eliminated by using ethylene glycol that contains inhibitors. Most commercial ethylene glycols sold contain these corrosion inhibitors. It is not generally recommended to use uninhibited ethylene glycols for heat transfer applications. If uninhibited ethylene glycol is used, it must be used with caution and carefully monitored.