I am using the Prestone Low Tox brand coolant (propylene glycol) - it's the
one that's less toxic to dogs and cats. I may be wrong but my understanding
is that this brand is phosphate free and the color is green. The auto parts
store folks assure me it is phosphate free and the container states it
protects alum heads - if anyone has different info I'd sure like to hear
about it. Joe