All you need to know about coolant

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There is more to coolant than meets the eye.

In the past five articles, we have discussed how automotive technology has changed forever. In recent years, the number of different motor oils available to consumers has multiplied exponentially, in order to keep up with the lubrication requirements of all the different vehicle manufacturers.

Oil specifications can also vary; not only from one car manufacturer to another, but also by the year, make, model and engine of the vehicle. And, no matter whether we are referring to engine oils, manual and automatic transmission oils, differential and transfer case lubricants, power steering fluids, coolants or brake fluids, the technology has changed.

Many of these changes will be of little concern to most owners of motor vehicles, who will simply deal with the results of having trusted a private workshop, or the agents, to use the correctly specified choice of fluid for their vehicle. And with this comes the understanding that footing unnecessary maintenance costs – and perhaps even ruining an engine – are all part of the deal. This is even despite the fact that owners are paying an arm and a leg for regular servicing, which they believe is being done properly, using the correctly specified fluids.

Having made this perhaps slightly negative statement, I believe that I should once again note that I have been in the oil industry for 25 years, and that, during this time, I have come across only a handful of workshops whose employees know something about oil − and who use the correctly specified lubricants, along with the correct service intervals, in their customer’s vehicles. This experience includes many OEMs (original equipment manufacturers) who, like the owners of private workshops, purchase one engine oil to use for servicing everything from a 1.2-litre petrol run-around to the latest direct-injection turbodiesel vehicle with a diesel particulate filter and extended drain interval of 50 000km. (The latter requires a very specific OEM-approved low-SAPS synthetic motor oil).

The brand and product used is determined by a combination of a vast lack of knowledge, a standardisation of product, and purchasing it at the lowest price – as opposed to the need to comply with the OEM specifications and requirements. Unnecessary and expensive maintenance costs will most definitely follow.


Which brings us to the subject of this month’s article: antifreeze or coolant – whichever term you prefer. Let’s begin by confirming that engine coolant is a generic term used to describe fluids that remove heat from an engine.

Antifreeze is a more specific term used to describe products which provide protection against freezing; not all engine coolants need to provide this protection. (Consider engines being used in tropical climates where you will always need an engine coolant but may not need the coolant to have freeze-protection.) However, so as not to further complicate an already weighty subject, we will use the terms antifreeze and coolant interchangeably.


Ethylene glycol was first prepared in 1859 by the French chemist Charles Wurtz.

The Rolls-Royce Merlin B engine (1935) was the first Rolls-Royce aircraft to use an ethylene glycol cooling system. In the early 1940s, the Merlin XII, fitted to the Spitfire Mk.II (Supermarine type 329), was cooled by a 70%:30% water/ethylene glycol mix. The reason glycol-based coolant concentrate cannot be used alone (or ‘neat’, if you prefer) is that it does not offer sufficient protection against heat transfer and corrosion.

To optimise the heat transfer and other functional attributes, a coolant concentrate must always be diluted with high-quality water, preferably deionised water, in a 50:50 ratio. Coolant concentration should never be less than 30% strength, as this would compromise coolant performance significantly.

For the budding chemists out there who want to know how ethylene glycol combines with water, a basic explanation follows. Ethylene glycol or 1.2-ethanediol (mono-ethylene glycol) is structurally quite similar to water. It comprises two linked carbon atoms, each bearing a hydroxyl (or OH-group). Because of these hydroxyl groups, it can form hydrogen bonds between molecules in the same way that water does. This makes it miscible with water in all proportions. The freezing point of pure water is 0°C, as we all know, and the freezing point of pure ethylene glycol is -12°C. But, when the two are mixed together, they interfere with each other’s attempts to organise into ordered solid structures, which stops the water from freezing − even down to about -50°C – in a 70% ethylene-glycol mixture.


Perhaps the place where the cheapest coolants are supplied, and where you will find the biggest variation in quality in conjunction with a severe lack of information on the labels, is in spares shops. Private workshops come in a close second. Coolants that are sold in five-litre containers have been “bulk purchased” from a local plastics company. It is in these containers that we can purchase fabric softener, dishwashing liquid, pine disinfectant and a host of other chemicals for the home, at discounted prices. The labels on this antifreeze container (when legible and still in place) typically state only the obvious: Antifreeze. Not one specification or approval is shown, or the percentage of ethylene glycol contained in the formulation. Neither is the type of corrosion inhibitor shown. In OEM-approved antifreeze, these corrosion inhibitors include nitrites, phosphates, silicates, amines and more.

Many automotive manufacturers (for example, VW and Ford) will specify a coolant that is nitrite-, amine- and phosphate-free for some of their models. However, the same two manufacturers will also recommend coolant that is silicate, borate, nitrite and phosphate-free for other models, and a coolant that is amine and phosphate-free for yet more models. However, according to many spares shop and workshop employees and owners, this one green antifreeze will work in all these applications!


At least six different types of OEM recommended  antifreeze formulations exist − seven if we include food grade antifreeze − and each employs the use of completely different corrosion inhibitors. This number excludes the variations on the six antifreeze types mentioned, where each allows the motorist to choose (within the required OEM specification) from options such as concentrated coolant, a 50:50 premix to -40°C, a hot-climate 50:50 premix to -15°C, and a very-cold-climate option of a 60:40 premix to -60°C. This brings us to a total of 25 coolant/antifreeze options available. In addition, besides ethylene glycol, there are also coolants like 1, 3-propanediol, otherwise known as PDO, and Glycerine (Glycerine/Glycerol).


As a matter of interest, food-grade antifreeze includes propylene glycol, as opposed to ethylene glycol, although both are used in automotive coolants. The Food and Drug Administration (FDA) has classified propylene glycol as “generally recognised as safe”, which means that it is acceptable for use in flavourings, drugs and cosmetics, and as a direct food additive.

Ethylene glycol, on the other hand, is a particularly nasty chemical: when ingested, it affects the central nervous system, the heart and the kidneys, to the point that it can ultimately prove lethal. Because of its sweet flavour and aroma, thousands of wild animals, pets and children are poisoned by drinking automotive antifreeze/coolant every year.

Ethylene glycol is found not only in antifreeze. In very cold climates, it is a component of de-icing solutions, and is found even in carpet and fabric cleaners. According to results from animal studies, the ingested amount of ethylene glycol required to produce toxicity is approximately 1.0 to 1.5ml per kg, or 100ml in an adult. Even very small amounts of antifreeze can be fatal.

Although two or three tablespoons can kill an average-sized dog, walking through antifreeze and then licking its paws can kill a cat. However, when treated appropriately, patients have survived much larger ingestions. If you or your pet are unlucky enough to drink antifreeze by accident, then it is important to get medical attention urgently. Because its structure is similar to that of ethanol (or alcohol) ethylene glycol initially makes you very drunk very quickly, but also makes you nauseous and likely to be sick. As the body tries to metabolise the toxin, its hydroxyl groups are oxidised to carboxylic acids. This spreads the effect into the nervous system and can cause increased heart rate, high blood pressure and even heart failure. After around 24 hours, the kidneys will begin to fail under the strain.

Fortunately, treatment for ethylene glycol poisoning is relatively straightforward if the diagnosis and treatment occur quickly. The enzyme that is responsible for converting ethylene glycol into its toxic metabolites is the same one that metabolises alcohol, but its affinity for alcohol is 100 times higher. Therefore a large dose of alcohol (Fomepizole, specifically; not a six-pack of Heineken) usually given by intravenous drip, can saturate the enzyme and prevent it from converting the glycol into more toxic compounds. This may stop the poisoning, but it would probably be safe to assume that when you woke up, it would be with the mother of all hangovers.

For those who want to know why we still use ethylene glycol if it is such a toxic product, the answer is simple. Ethylene glycol-based fluids, when used as directed, offer the most cost-effective performance advantage. In other words, ethylene glycol is cheaper than propylene glycol.


Ethylene glycol on its own will not suffice as a coolant. The composition of antifreeze/coolants includes water, freezing-point depressants, corrosion inhibitors, antifoamants/defoamants and stabilisers to prevent scale formation and flocculation or polymerisation of the inhibitors, anti-scaling agents, silicate stabiliser and pH buffers. Poor-quality antifreeze contaminates the entire cooling system and eats away at metal, rubber, and plastic components. Obvious external indicators are bulging antifreeze hoses, and white, calcified residue oozing from antifreeze hose-clamp mating areas. Also, lime and scale deposits can begin to build up in the radiator core, restricting the flow of antifreeze and causing the engine to run hotter, especially in summer.

Specified coolants are based on the design and materials used in those engines and the interaction of the fluid with those materials. Using the incorrectly specified coolant or low-quality coolant can lead to head gasket failure, liner pitting in diesel engines, water pump failure/water pump seal failure, damaged cylinder liner seals, cylinder head cracks and holes, destroyed welsh plugs, radiators and heater cores, and result in other cooling systems components being eaten away.


One of the questions I am asked frequently is whether or not we need anti-freeze in South Africa. To be 100% accurate, this statement made to me, and believed, by many vehicle owners – is that we do not need anti-freeze in SA. The truth is that, regardless of the climate, it is recommended that all engines use glycol-based coolants.

Just because a particular environment may not experience freezing temperatures does not mean that other concerns such as boiling point, evaporation, corrosion Let’s consider the boiling point. During engine operation, the cooling fluid must possess the ability to remain a fluid when it is heated during operation. It must resist the tendency to boil and form vapours. Vapours do not have the same heat-transfer capabilities of a liquid, and vapours therefore reduce the fluid’s ability to transfer heat. Glycols mixed with water extend the boiling point: typically, to more than 150°C.

The main function of a coolant is to provide effective heat transfer in order to remove excess heat from an internal combustion engine. A running engine typically converts only one third of the energy derived through the combustion of fuel into work, which moves the vehicle.

The other two thirds are converted into heat, of which one third goes out through the exhaust. This leaves the remaining third in the engine block, which needs a coolant to absorb this heat, transport it to the radiator and then dissipate it into the environment. Because of the removal of this heat by the coolant in the cooling  system, the engine is able to operate in an efficient manner: the fluid therefore “cools” the system.

Additional functions of a coolant/ antifreeze include protecting the system from freezing, protecting the system from overheating and protecting the cooling system from corrosion. An engine coolant therefore contains mainly three components: Ethylene glycol or propylene glycol + deionized water + corrosion inhibitors.

The colour means nothing; it is not an indicator of the type or quality of an antifreeze. In fact, before dye is added, all coolant is colourless. Individual manufacturers differentiate their own coolant types or specifications by adding colour. Improper dilution of the coolant concentrate is a common problem, resulting in overheating and corrosion.

Ethylene glycol has a very long service life, but the corrosion inhibitor additives do not. As the well-known traditional green coolant inhibitor systems become depleted by forming a protective layer, they need to be changed, typically every two years. Extended-life carboxylatebased coolants (also known as OAT) will last five or more years. These are based on carboxylate inhibitors and provide protection from corrosion by chemically interacting with the metal surfaces where needed, and not by universally laying down layers, which is the case with conventional and hybrid coolants.

Tap water contains contaminants that can lead to scaling, corrosion, and cracking of radiator tubes. Always use deionised water in a cooling system with coolant, as it is free of dissolved minerals such as calcium and magnesium which contribute to scale formation, which in turn impedes the efficient functioning of the cooling system and leads to engine failure. A 1mm layer of scale has the same insulating effect as 75mm of cast iron and acts as a major insulator which does not allow heat to dissipate easily from your engine. Polymeric additives in coolants also inhibit the deposit of minerals by coating these particles so that they cannot attach themselves to engine surfaces.

It is important not to mix different antifreeze types. Each antifreeze has its own corrosion inhibitors. For example, adding a conventional coolant into extended-life antifreeze will diminish its extended service life characteristics.


With all the different corrosion inhibitors available in coolants, the selection is no longer a simple one – what with Hybrid Technology Coolant (both inorganic and organic corrosion inhibitors) Traditional Technology Coolant, Organic Acid Technology (OAT) and Hybrid OA Technology (HOAT), it is best to take some care in selecting. When it comes to antifreeze/coolants, always use a reputable and endorsed product that meets the requirements stated in the owner’s manual of your vehicle. If it’s cheap, there is going to be a very good reason why.


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