A Study of Extension of Engine Coolant Life Using Low Phosphate Organic Acid Inhibitors

A prescription was developed for a long-life engine coolant that included certain amounts of added organic carboxylate inhibitors and inorganic acid inhibitors, showed zero blackening of aluminum, and lowered effect on cooling system components and materials. A method of judging coolant life was also developed.

As a reference, non-phosphate organic acid type coolant (NP-OAT coolant) was also investigated, but because degradation in erosion-corrosion toughness accompanying aluminum blackening was found, it was necessary to add inorganic acid inhibitors including phosphate inhibitors. Also, the cause of the erosion-corrosion was judged to be amorphous corrosion by-products from aluminum blackening at high temperatures due to non-phosphate organic acid inhibitors, according to a comparison analysis of these with phosphate-type inhibitors.

A catalytic process for heat-oxidation degradation of coolants was developed and established to correlate with aging in market vehicles. This can be used to estimate the lifetime of anti-corrosion performance of coolants in the laboratory.