Dear Tom and Ray: I'm not a rocket scientist, just a veterinarian, but I can't figure this one out. I have a 2000 Subaru Outback. The owner's manual tells me that I should only use ethylene-glycol-based antifreeze. But I know that stuff kills so many animals, and I want to use the animal-friendlier propylene glycol.
Tom: Sadly, most new cars now come with long-life, organic coolants. These are all ethylene-glycol-based, and they're all poisonous to neighborhood dogs and cats. And worse, they smell and taste sweet, so when this stuff leaks out of somebody's engine, animals lap it right up.
Ray: So, several companies (Peak's Sierra, most notably) came out with a safer coolant based on the chemically similar propylene glycol, which is much less toxic. Not everybody switched to it, because it's more expensive. But it's a perfectly adequate substitute for any car that uses regular old (non-long-life) coolant. In fact, it's probably fine for your Subaru. But some manufacturers will void warranties if you don't use the coolant they specify, so you shouldn't take that risk.
Tom: As far as we know, there are no long-life coolants -- which is what Subaru and others now require -- based on the safer propylene glycol.
Ray: But California and Oregon now require that any coolant sold in those states be "embittered," so that it tastes awful to dogs, cats or little kids. The manufacturers do that by simply adding a chemical "stink agent" that costs about 2 or 3 cents a gallon.
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