Review of Organic Acids as Inhibitors in Engine Coolants

Presented is a literature and patent review of organic acids as corrosion inhibitors for use in engine coolants. The technology is directed towards use of acid combinations or acids with conventional inhibitors because no individual acid can provide protection to the range of metals used in cooling systems. Some examples are: aliphatic monoacids with diacids, azelaic acid with aromatic acids, molybdate with two or more aliphatic acids, and sebacic acid with benzotriazole. Claimed advantages are non-depletion (‘long-life’ coolants), non-silicate (gelation and pump seal wear concerns) and non-nitrite (nitrosamine formation), and compatibility with ethylene glycol and propylene glycol.