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An inhibitor package which is silicate-, nitrate-, borate- and phosphate-free has been developed as the basis for a world-wide automotive coolant formulation. The formulation contains aliphatic mono- and dicarboxylic acids and tolyltriazole as the sole inhibitors. Formulations containing carboxylic acid inhibitors have been studied in ASTM bench tests and found to sufficiently protect all prevalent cooling system metals. In addition, fleet tests have shown that carboxylic acid inhibitors deplete much more slowly than conventional inhibitors, making possible a much longer life coolant. Results from laboratory tests which simulate extended usage indicated that carboxylic acid-containing coolants have a significantly longer life span for the protection of all cooling system metals. Finally, the carboxylic acid/tolyltriazole inhibitor package is completely adaptable to a propylene glycol base.

High lead solder coupons are frequently tested in ASTM D 1384-87 and D 2570-91 tests to determine the corrosion protection provided by engine coolants. In contrast to 70/30 solder, high lead solder is often observed to show relatively high corrosion rates in D 1384-87 testing. Surprisingly, the high lead solder corrosion rates tend to be lower in the D 2570-91 test, despite the longer duration of this test. The basis of this effect has been investigated in different coolant formulations and in both ethylene glycol and propylene glycol. The corrosion of high lead solder was found to be directly related to the presence of oxygen in the D 1384-87 test. Replacement of the air purge with a nitrogen purge significantly reduced the corrosion rate of high lead solder in inhibited coolants. These results are interpreted in terms of the solder composition.

Automobile coolant pump failure rates have been observed to be influenced by the coolant inhibitor package. A fleet test consisting of 196 1991 Ford Crown Victoria taxi cabs was utilized to test six coolant formulations. Four of the test formulations were monobasic/dibasic organic acid technology coolants and two were traditional technology coolants containing nitrate, phosphate, and silicate. Coolant pump failure rates were monitored as a function of mileage. Results indicate that the service life of coolant pumps for those systems employing organic acid technology coolants was significantly greater than those systems utilizing traditional inhibitor technology coolants.