99% of the coolants produced are ethylene glycol-based. Globally, there will continue to be innovation on corrosion inhibitor technology as engine metallurgy or cooling system requirements change; but it's unlikely ethylene glycol will ever have a serious contender to replace it. EG is readily available worldwide, well priced (compared to any contenders) and provides the best coolant parameters of any of the glycols. And now that embittering agents are added, ethylene glycol is here to stay.
Well over a hundred years ago, the internal combustion engine was invented. It changed mankind forever – gave him mobility and gave him a mechanical horse to work construction, mining and agriculture. With the combustion engine came heat that had to be dissipated. The early engines were not that powerful and could be air cooled.
The desire for more power led to bigger platforms that could not be cooled with a fan. So, the next step in engine evolution was liquid cooled systems; and, fortunately, the most efficient and cheapest liquid heat transfer media is water.
While liquid water is a good heat transfer media, the amount of heat it can absorb is limited on the high side by its boiling point. For the most part, this can be easily addressed by pressurizing the system (which raised the boiling point) and by designing a radiator of sufficient size and air flow to dissipate the heat collected in the water.
But the more insidious problem is that water freezes at a relatively high 32° F, a temperature below which most of the United States will reach each winter. Even worse, water is one of actually very few liquids that expands upon freezing. The hydraulic pressure this puts on a liquid full system or space creates enormous damage. This freeze/thaw action accounts for much of the road damage in the U. S, many burst pipes during the winter and potentially destroyed cooling systems if measures are not taken.
So something had to be done to protect the cooling system as the use of and demand for vehicles in all seasons began to grow. A chemical was needed to add to the water to lower the freeze point and equally important prevent expansion if the cooling system did freeze. Fortunately, that chemical existed and was well known . . . methanol.
So, yes, that’s right. The alcohol that today is the principal ingredient in windshield wash was the first cooling system antifreeze. A 40% methanol/60% water solution has a freezing point of -39° F. Methanol did present a new problem, however, because it had a lower boiling point than water (165° F) . . . summer boil-over. The solution to this problem was somewhat simple: use the methanol/water mix in winter and remove it and use pure water in the summer when freezing was no longer a concern. So, for quite some time, that was the way combustion engine equipment was handled . . use water in the summer, add methanol in the winter and change back to water only in the summer.
Then about eighty years ago when environmental laws were mostly non-existent, a chemical company noticed a stream into which they discharged effluent (it was common practice back then) no longer froze in the winter. This company investigated this phenomenon and discovered the chemical that prevented water from freezing was ethylene glycol. And even better, ethylene glycol had a higher boiling points, much higher than water. Eureka! – A chemical that both lowered the freeze point of water and raised the boiling point so the coolant mixture would not have to be removed in the summer. This was the birth of . . . Permanent Antifreeze and was the first big marketing claim by all the antifreeze manufacturers. Of course, because of the need for corrosion inhibitors, coolant did have to get changed periodically, but that is a different story. As a result of this discovery, a new chemical business was born for ethylene glycol.
Decades later, polyester for clothes, bottles and camera film was developed which used ethylene glycol as a raw material. The polyester industry has grown so much that 90% of all EG made goes to make polyester. But this large supply base has assured EG is readily available and is economical to use in antifreeze/coolant.
So ethylene glycol/water would rule the coolant world almost exclusively right up until today. If there is any one drawback to ethylene glycol, it is toxicity. In the 1990s for some reason, ethylene glycol poisoning was said to be a concern for humans; but even worse, hundreds, maybe thousands, of pets died each year from drinking or licking up spilled antifreeze around cars. As part of this new concern, in 1991 Oregon passed a law requiring an agent to be placed in antifreeze (and windshield wash) to make it taste bad to prevent these poisonings. This law was named after a child who allegedly had lost a pet to antifreeze poisoning. The antifreeze manufacturers came together under the Consumer Specialty Products Association (CSPA) and launched several independent investigations, which ultimately showed there had been no accidental human poisonings ever and at most two to five cases a year of pets ingesting antifreeze and perhaps one death a year to a pet. Nevertheless, over the next ten years, many states passed similar laws; so today all EG-based coolants contain an embittering agent, which costs the industry millions of dollars a year, even though there is no verified threat to humans and . . . get this . . . even though animals do not have the taste buds for bitter and would not be deterred by the now bitter taste of antifreeze.
What was known as Arco Chemical, later Lyondell, used this unfavorable notoriety on EG toxicity to introduce propylene glycol-based coolants. Propylene glycol also reduces the freezing point of water while raising the boiling point of the mixture. The freeze point depression with PG was not quite as good; a 50/50 PG water mix freezes at -28° F compared to a 50/50 EG/water mix that freezes at -34° F. But PG offered one significant property: it had so low a toxicity, it was on the GRAS (Generally Regarded as Safe) list. Today, PG is used in many everyday products and is even the ingredient in “soft” pet foods that gives it the soft/moist appearance.
So almost all antifreeze/coolant companies began to offer a PG-based coolant, and significant marketing was performed to extol its low toxicity benefits. Old World introduced what was probably the most successful PG coolant, Sierra Antifreeze. But PG had one fatal flaw. PG is a much smaller item of commerce than EG and is made via a different chemical process. For both these reasons, PG is more costly than EG and depending on their respective market positions, can add anywhere from $1.00 to $4.00 to the manufacturing cost of a gallon of antifreeze.
As a general rule, the consuming public will always pick a safer alternative of any product if priced comparably but will not always pick the safer alternative at a higher price. So this higher cost and the fact all EG coolants were embittered made it very difficult for PG-based coolants to get and keep a significant position in the coolant market. Today, PG coolant is only used in what would be considered high toxicity risk areas like wild life or amusement parks or by consumer or farm areas that have a great concern for animal/pet safety. Today, PG coolant represents only about 1% of the total coolant market.
Other chemical manufacturers have come forward with their glycol of choice to garner a share of the coolant market. Traditional propylene glycol is a three carbon molecule with an alcohol group attached at carbons #1 and #2. One can also make propylene glycol with the alcohol groups attached to end carbons #1 and #3. This form of propylene glycol is called Propane Diol (PD) to distinguish it from traditional 1 and 2 propylene glycol.
Propane diol provides the same freeze point, boil point and low toxicity benefits of traditional PG along with the added benefit of being more chemically and oxidatively stable. This means a coolant made with propane diol will last longer. However, the manufacturing route to propane diol is even more difficult and costly than that for traditional PG, so hence PD is more expensive than PG. So again, despite a considerable marketing effort by PD manufacturers, PD coolant is less than 0.1% of the market.
One other glycol that has been given a serious look by the industry is glycerin. Glycerin is also a three carbon molecule with an alcohol group attached to all three carbons. Where EG, PG and PD are diols, glycerin is a triol.
Glycerin can be made synthetically but is also a large by-product of biofuel production. Glycerin also depresses the freeze point of water and raises the boiling point as well. It is readily available and has such low toxicity that it is used in hundreds of products, including lotions, gels, drinks and food products. So human consumption is not a concern.
The price of glycerin has fluctuated quite a bit but at times has been close to parity with EG; so it would seem to be a good, very low toxicity option for making safe coolants. Since this looked so promising, several coolant manufacturers and OEMs worked on developing a glycerin-based coolant.
But glycerin had its drawbacks as well. Glycerin does not depress the freezing point of water as efficiently as EG – a 60% glycerin concentration is required to get to the same -34° F as a 50% EG formula. That adds cost. And glycerin is as viscous as honey. Either it has to be shipped and stored in a heated tanker or diluted with water. This means a concentrate antifreeze based on glycerin is impossible – only prediluted coolants can be made, stored and shipped. Glycerin is also very bio-active, meaning it is a great medium for growing all kinds of fungus, bacteria, almost anything; so an agent must be added to prevent this . . . more cost.
And lastly, through a variety of studies, it was shown the purity of the glycerin affected the coolant’s performance. Below a certain purity the glycerin-based coolants would degrade more rapidly than their EG counterparts. Higher purity means higher cost. The solution to all these glycerin drawbacks was to consider a coolant that was a mixture of EG and glycerin although the advantage of low toxicity would be compromised.
So, today there is only one approved glycerin coolant, which is 80% EG/20% glycerin. This coolant is not readily available to consumers, and glycerin prices have risen over the years. Despite much research, glycerin has not formed any significant position in the coolant markets.
So here we are, almost eighty years after ethylene glycol was first introduced in antifreeze with the first claim of a “permanent” antifreeze, that still 99% of the coolants produced are ethylene glycol-based. Globally, there will continue to be innovation on corrosion inhibitor technology as engine metallurgy or cooling system requirements change; but it unlikely ethylene glycol will ever have a serous contender to replace it. EG is readily available worldwide, well priced (compared to any contenders) and provides the best coolant parameters of any of the glycols. And now that embittering agents are added, ethylene glycol is here to stay.