A QUESTION OF COOLANT
QFor my Fifties to Seventies cars I’ve always used blue antifreeze that needs changing every two years. Is this because its antifreeze properties deteriorate, or its corrosion protection? Does increasing the concentration increase corrosion protection? I see Prestone antifreeze is being sold as universal to mix with/ replace all types of antifreeze. It seems to have advantages – it lasts 10 years and one only needs a single type in stock.
Julian Parsons, via email
Martin says:
ABlue antifreeze is ethylene glycol. Its freezing point remains fairly constant with age.
The corrosion inhibitors do deteriorate, however, and this explains the two-year change interval. Even at the lowest recommended concentration of one part antifreeze to three parts water, corrosion protection is perfectly adequate. Antifreeze appears to have a reasonably long shelf life, which doesn’t shorten its two-year service life in the engine. Prestone’s antifreeze formula is a mystery to us, as the manufacturers give nothing away in its literature. We note that HOAT (hybrid organic acid technology) antifreezes have a 10-year life and an anticorrosive package similar to that of ethylene glycol, so maybe it’s related to that. The claimed 10-year life will have been tested on sealed cooling systems. It may suffer oxidation in older cars that have an air space in the radiator, so you might want to stick with the good old blue stuff.