Technique and elaborations Sun 02 July 2017

The coolant par excellence

The coolant par excellence?

Which characteristics should have the ideal coolant? Great ability of heat exchange, high boiling temperature, ideal viscosity to flow inside small section pipes and, always relished characteristic, a contained price: we’re talking about water.
Talking about performance it's the best, but unfortunately the freezing under 0° makes it unusable during winter, when the operating temperatures can drastically decrease under the freezing limit. That's why the most common term to identify coolants is “antifreeze”.

What is it made of?

In most cases, today the antifreeze is made of monoethylene glicol (in some cases also propylene); a mixture with a relationship 1:1 water/glicol ethylene allows the freezing temperature to decrease, also reaching less than -30°, and to improve the boiling temperature of 15%.
As well as water, glicol can't remain pure: because of heating and freezing cycles it chemically decomposes to organic acids, strongly corrosive for metals, when not inhibited by basic ingredients in the mixture. The additives usually were for this reason nitrite, phosphate and silicates… in addition to these, useful to make the chemical environment basic inside the radiators, the presence of more additives lends ability of lubrication and reduction of the cavitation phenomenon (more easily, the tendency of a moving liquid to make foam).

What does the colors indicate?

Different types of additives gives life to different families of cooling liquids.
Once the coloration of the antifreeze was to distinguish the two basic typologies, red for methanol and blue for the glicolic base, but today it's no longer like that; methanol is no longer used because of its volatility (it needed to be substituted too often).


Blue/green color is still the indicator for liquids made of glicol, plus above saline additives.


The enormous diffusion of radiators and light alloy components, brought to the development of chemically more gentle liquids with aluminum: the result is HOAT antifreeze liquids (Hybrid Organic Acid Technology) which is indicated by

yellow-purple coloration, in which some salts have been substituted by organic components. Collateral result, since the use of acid organic substances, is also to have a more eco friendly liquid.

The next step is the implementing of exclusive organic additive liquids, the OAT (Organic Acid Technology): characterized by orange-red colorations, compatible with yellow-purple liquids, but not with the blue/green ones.
Most coolants commercially available nowadays are OATs, HOAT are a bit more dated, while blue/green liquids are more and more less spread on the market and are disappearing.

What happens if I mix liquids of different color?

Maybe this is one of the most frequent questions that do-it-yourself costumer ask. Producers’ attention in differentiating the colors already suggests a risk if things are not made as they should.
Talking about mixing different colors, the operation is possible between compatible liquids (yellow-purple with orange-red) but it could cause a small reduction of the cooling efficacy.
It's absolutely to avoid the mix between blue/green liquids with all the other ones: there's the risk of chemical reactions between the different additives, which can also lead to the formation of gelatinous compounds, which doesn't have cooling properties, doesn't flow well inside the tubes, and risk to compromise completely the operation of the whole system.

What should I do in case of emergency?

Assuming that it would be appropriate to follow the indications of the manufacturer, which suggest a check before leaving, yet it could be necessary a temporary refill. In this case nothing is better than water… it's the basis of every antifreeze mixture, and for a short stay in your radiator it doesn't need to be demineralized… to go back home almost everything is good, then a system’s washing will be enough.

Does my liquid need to be substituted?

A great way to check the health condition of our own antifreeze it's to check its limpidity: an antifreeze liquid that has been contaminated by other incompatible liquids, before decomposing into gelatinous compounds, becomes turbid; it obviously needs to be completely replaced and the system needs to be rinsed with water (better if demineralized).
Insufficient limpidity could also be symptom of old liquid, exhausted because of the heavy and long work on the engine but pay attention, because the contrary is not always true: a very old liquid could have perfect visual conditions (with lovely colors and great limpidity)… unless measuring the PH with laboratory tools, in this case it os difficult to evaluate the health condition of the solution: since the cost is derisory (an enduro motorcycle usually contains less than 1,5 l of coolant) it is rated to change it at least once a year, in case of amateur use.

What if I only use the motorcycle during summer?

As explained before, despite the term “antifreeze”, the coolant has many functions: it's anticorrosive, it reduces bubbles and foam, it lubricates the water rotor, preserves in good conditions the rubber parts ecc…, it's highly suggested the use during the whole year. The less efficiency of an antifreeze towards pure water doesn't need to cause worries: if on the one hand it's true, as said, that water is pretty much incomparable in matter of performance, on the other hand it's also true that the gap is not enormous, and that every engine of the last three decades has been realized also considering this aspect…if you look for a greater cooling capacity, it is better to search for other solutions, like fans, larger radiators and so on.
On some contemporary enduro motorcycles the system is also split into two and controlled by a thermostatic valve: when the engine is cold the valve is closed, only one radiator works until reaching a certain temperature, then the valve opens and also the second radiator starts working. This is useful to allow the the cylinder to heat more quickly, but as a side effect it has one more component that can damage: if you don't decide for the valve removal, the use of a cooling fluid is necessary to lubricate it.

The use of pure water is planned (and regulated very precisely) for competitions (or training shifts) on asphalted tracks, where, in case of leaks, it would be really dangerous for the other users, creating a slippery coat on the asphalt.


Text by Alessandro Manna