It's propylene glycol (PG) antifreeze, sold under the "Sierra" brand name. Every other brand of antifreeze contains ethylene glycol (EG).
Antifreeze made with propylene glycol is being marketed as a "safer" alternative to ordinary antifreeze. Though it is by no means safe to drink, it is significantly less toxic than ordinary ethylene glycol antifreeze -- which may be a important difference to pet owners and parents of small children. PG also has an unpleasant taste which discourages further sampling by thirsty animals and toddlers. Safety is an important issue with coolants because of the frequency of spills, leaks and improper disposal.
According to one supplier of PG-based antifreeze, over 3,000 people in the U.S. were treated for ingesting antifreeze in 1991 (the latest year for which figures were available). Eight of them died. Had the antifreeze they ingested contained PG instead of EG, the consequences may not have been so dire.
Because of its significant safety advantages, PG coolants represent far less risk to wildlife in case of spills, leaks, or careless disposal. Because of this it can be claimed that PG coolants have an environmental benefit. However, both PG and EG are biodegradable and both may pick up lead or other heavy metals once they've been used in a cooling system. Both types of coolants, after being used, should be disposed of properly and in compliance with local regulations.
Though some auto makers were initially cautious about using PG when it was first introduced, GM has now said that propylene glycol may be used in GM vehicles without voiding the manufacturer's warranty coverage and will perform adequately under most vehicle operating conditions. Most vehicle manufacturers, however, don't currently use PG as a factory-fill antifreeze because of its higher cost (about $1 more per gallon at retail).
When mixed with water (50/50 ratio), ordinary ethylene glycol antifreeze provides freezing protection to -34 degrees F. and boilover protection to 263 degrees F.. By comparison, propylene glycol provides freezing protection down to -27 degrees F. in a 50/50 mixture and boilover protection to 257 degrees F.. Though it might be argued that PG provides a few degrees less protection than EG, the difference can be easily offset by using a slightly higher concentration of PG in the coolant mix.
In terms of thermal efficiency (heat transfer), both types of antifreezes perform about the same (though EG has a marginal edge). Corrosion protection is about the same as long as the coolant is properly formulated with inhibitors.
ANTIFREEZE DISPOSAL & RECYCLING
Regardless of the type of antifreeze you use, it should be disposed of properly. In many areas, it is okay to flush used coolant down the toilet (sanitary sewer) as long as the amount does not exceed a few gallons. But it should not be poured down a floor drain or into a storm sewer.
Both types of antifreeze are biodegradable but take some time to break down. Dumping used antifreeze into a storm sewer, ditch, creek or on the ground can contaminate ground water and kill plants and fish. What's more, used antifreeze picks up lead from solder in copper/brass radiators. Lead is a toxic heavy metal that can also cause pollution problems of its own.
Some areas prohibit ANY dumping of used coolant (sanitary or storm sewers). They also may not accept used antifreeze in a sealed container for landfill collection because eventually the container will leak its contents into the ground causing possible ground water contamination.
So how do you get rid of the stuff? You can take it to a local collection center that accepts used antifreeze for disposal or recycling, you can pay to have it disposed of as a hazardous waste (yeah, right) -- or you can take your vehicle to a garage or service facility that has a coolant recycling machine. The latter is the best choice because it eliminates the disposal problem altogether.
Coolant recycling machines work their magic by a variety of means. Some use filtration while others use a distillation process to remove the harmful contaminants from the old antifreeze. Corrosion inhibiting chemicals are then added to restore the coolant's corrosion protection. The auto makers have all approved coolant recycling as an effective means of eliminating coolant disposal problems, and each publishes a list of machines that meet their specifications. Recycled coolant must meet minimum standards of purity before it can be reused.