Question: I've heard about a new "environmentally safe"
nonpoisonous antifreeze. What is it?
Answer: 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 more per gallon at retail).
PERFORMANCE COMPARISON
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.
