The inorganic/organic/hybrid corrosion inhibitor packages have nothing to do with environmental friendliness. They are different corrosion inhibitor strategies. Sierra is propylene glycol based. Propylene glycol is still toxic, but you or your dog would have to drink more to get sick or kill yourself. Sierra brand advertising is just hype. You are not "helping the environment" by using it, and you may well be damaging your cooling system. I have no idea what corrosion inhibitor technology is present in Sierra brand, and I would never consider using it.

I don't know DC's position, but GM specifically recommends AGAINST the use of propylene glycol antifreezes because propylene glycol has different thermal capacity than ethylene glycol. Most OEs design their cooling systems to operate best both in terms of heat transfer and corrosion protection with a 50/50 mix of commercial antifreeze and water.

If you do your own coolant changes you should check with your local authorities as to how you should dispose of old antifreeze. In my city it is okay for homeowners (but NOT commercial shops) to dump old antifreeze down sanitary drains (like the toilet) because we are connected to a state-of-the-art sewage treatment plant that breaks down the glycol and removes any heavy metal ions like lead. You should NEVER dump antifreeze down storm drains, septic tank systems, or in the woods.

I am not aware of any OE who approves recycled antifreeze, and most specifically recommend against it. Think about this. Do you trust some local shop to use a machine to "purify" and then add a proper concentration of the OE's recommended corrosion inhibitors over the ability of a major chemical company to produce a consistent quality product that is properly formulated to what the label says it is? I would never personally use "recycled antifreeze" and would never recommend it to others.

Most of the local auto parts chain stores in my area now carry Zerex G-05. If you can't find it go to the Valvoline web site and see if they have a list of retailers. Im not personally aware of any other brand product except G-05 (and MB brand) that meets the DC spec.

Duke