The technical cooling fluid is a very precise blend that has developed over the years for better performance and pollute less. We will see what the colors of the antifreeze are, what it contains, how to dilute the concentrated radiator fluid and what are mistakes to avoid.

Car coolant, what you need to know?

The engine cooling system is an essential element in any petrol engine vehicle. The combustion chambers reach very high temperatures, while the engine is designed to run at a certain operating temperature and must not overheat. For this, the engine cooling circuits are designed to bring the engine to temperature and keep it at the ideal temperature.

In the cooling system, the operating fluid is the coolant, which, as we will see, must have some characteristics, which also depend very much on the operating conditions and the geographical areas in which the vehicle is located. In fact, antifreeze is not only used to prevent the fluids from freezing, on the contrary, but it also has a lot to do with the boiling point and the thermal capacities of the fluid itself.

Each cooling system requires due attention and maintenance. For example, it is essential to wash the radiator to avoid encrustations or eliminate fluid traces if and when the product is changed. Or it is also important to check the engine cooling fan, which intervenes when the car does not drive much, and the engine warms up. If the fan does not work, you risk serious consequences for the engine.

Car antifreeze, what does it contain?

The technical fluid of the cooling system is a mixture of water, glycol, and additives. Water is the main element. It is generally recommended to use distilled water, although tap water is also accepted in some countries. The limestone present in the latter, however, is dangerous because it clogs the radiator fins.

Glycol, an ethylene or propylene alcohol, serves to change the thermal thresholds of the fluid. The freezing point is lowered, so the fluid resists better in winter, and the boiling point is raised, so no vapor is created in the various circuits. Finally, the additives can be of various types. Generally, they are rust inhibitors, which dissolve limescale residues and prevent corrosion to the engine and radiator.

The radiator fluids are marketed in different colors, and this is an aspect that can be confusing. The colors are not the result of the imagination of advertisers. They have become a convention, both to better identify any possible leaks from the machine (a transparent liquid is easily exchanged with condensation water), and to better match any top-ups, even if this is not always the case.

Engine coolant, colors

Blue Radiator Fluid (IAT) is an ethylene glycol fluid with inorganic anti-rust additives. These are very polluting and toxic elements, such as nitrates, phosphate salts, silica, and borate. The acronym IAT stands for Inorganic Additive Technology. It was a color widely used in the 90s, one of the first to come into circulation, today it is only found for topping up in old cars, but it has become too toxic for modern vehicles.

The yellow radiator fluid (HOAT) is a fluid with mixed additives, both organic and inorganic. A compromise compared to only very toxic inorganic additives (it contains some silicates and some phosphates). It is a hybrid fluid, which uses a Hybrid Organic Additive Technology. Green radiator fluid is a glycol-based fluid with silicates, used a lot by Dacia and Renault, less so by Hyundai, Nissan, and Citroën. The color can be very light and should not be confused with yellow.

Red radiator fluid (OAT) was introduced in 1997 and is one of the most popular technical fluids in modern models. It is a product containing only organic additives, hence the acronym, which means Technology with Organic Additives (Organic Additive Technology). There are no phosphates or silicates. On the American market, the color may be slightly different, that is, an orange radiator fluid.

The purple/lilac radiator fluid is a very recent product used in particular by Volkswagen, it is compatible with all products of previous generations. Ethylene glycol is partly replaced with glycerin, which has less impact on the environment, especially for production (lower carbon footprint).

Radiator fluid

How to choose the right radiator fluid

To increase the service life of your engine, it is imperative not to use the wrong radiator fluid. In addition to color, some car manufacturers have introduced compatibility codes with the antifreeze fluid G12 (1996) and with the antifreeze G13 (2008). The abbreviation G11 includes all the old antifreeze, blue, yellow, and green. The abbreviation G12 indicates products with organic additives, red (G12) or purple (G12 +, G12 ++).

These classifications are introduced at the end of the millennium (the G11 dates back to 1994, the G12 ++ to 2005) to indicate glycerin-based technical fluids, with an 11% lower environmental impact than glycol-based antifreeze. G13 antifreeze is lilac in color and contains silicates to protect aluminum, so it is not the ideal product for old copper/brass radiators.

The machine manufacturer always recommends the cooling fluid in the technical manual, but there are always alternatives, sometimes equivalent or better. The important thing is that the new product respects the same technical characteristics, the same parameters as the one indicated by the car manufacturer.

Also read: How to find the best models of the diesel engine?

Cost and method of refilling

To make a small top-up, you can also intervene with a little distilled water, while for the purchase of the fluid, you can go to any service station, hypermarket, or even online. Prices per liter are very different, from a few euros to € 20 per liter, depending on the type of product (color), concentration, brand, and therefore quality.

The concentrated radiator liquid must be diluted with distilled water following the proportions indicated in the product. Although these products are very available and easy to buy and handle, it must always be remembered that antifreeze is poison for the airways as well as for the environment. So you have to protect yourself and operate in a well-ventilated environment.

The golden rule is to always respect the proportion (for example, 50:50) with the distilled water and never mix antifreeze of different brands and colors. The concentrations are different in the various products; it is tough for different fluids to have the same parameters. Calculating the ratios to create the mixture with water and products of different nature becomes much more complex than buying an extra bottle.


Always follow the machine manufacturer’s instructions when choosing the coolant, always choose quality products, avoid mixing different antifreeze, regularly check the levels to have a cooling system always in excellent shape.