Behaviour of four ethylene glycol antifreezes in car tests

Some 80 tests were made in 18 diesel lorries and 33 petrol-driven vehicles during ordinary service performance. The formation of rust and the changes in pH and chemical composition were followed during more than a year. The distance driven in each test varied up to 100,000 km, the median being 15,000 km. The reproducibility of results was low, but common trends were clearly distinguishable. Where excessive corrosion occurred, it began rather suddenly, without any noticeable change in pH. Clean cooling systems were easier to protect from corrosion than were systems already corroded. Some depletion of inhibitor components was observed in all tests and pH tended to drop at the end of tests of long duration. Antifreeze containing sodium benzoate and sodium nitrite afforded the most reliable protection. Antifreeze inhibited with triethanolamine phosphate and the sodium salt of mercaptobenzothiazole gave good protection until the inhibitors were depleted; the marked irregularity with which this occurred made this antifreeze less reliable. Antifreeze containing these components plus borax behaved in much the same way. Antifreeze with borax as sole inhibitor did not seem to give reliable protection.