Antifreeze colour: when should you change the coolant?
Carboxylate-based antifreezes have the longest lifetime, up to five years. As for ordinary coolants, containing silicates, they need replacement every two to three years. But anyway, a car owner has to check the condition of the coolant once in a while, because it is quite likely that it will need replacement much earlier than declared by the manufacturer.
Why does blue antifreeze become green?
Currently there is a huge range of coolants on the market, for various car brands. The signal that the antifreeze has exhausted is that it changes the colour. Most commonly, during operation it gets a bright brown hue. This is a clear sign that the corrosion of the cooling system parts has begun, which occurs due to consumption of additives.
But it happens, for example, that a blue antifreeze changes its color to green sometime after adding. This occurs as a result of the destruction of the dyes it contains, because of prolonged exposure to high temperatures. E.g. when running at 95°C, the lifetime of a blue antifreeze is about 500-600 hours. But at a temperature of 105°C the antifreeze turns green almost immediately, and in 500 hours it’ll become yellow. Almost the same happens with red and green coolants, which gradually turn yellow and get a straw colour in the process of operation.
What do I do if the colour of antifreeze has changed?
The main purpose of automotive coolant is to protect the engine parts against corrosion and heat. In a situation where the colour of antifreeze has changed, it has little effect on its anticorrosive properties. You can keep using the coolant until it acquires an apparent rust-red hue.
Here are the other most common signs that the antifreeze needs replacement:
- stratification or the appearance of flakes;
- changes of density (measured by hydrometer);
- the appearance of a gel-like substance in the reserve tank.
Finally, remember that if you change the antifreeze type, the previously used coolant must be completely removed from the system. In addition, the system must be completely cleaned of sludge, scale and dirt. You can use an aqueous solution of a weak acid or distilled water. And finally, before filling up, don’t forget to dilute the concentrated antifreeze.