What is Coolant?

[VanRuth]

Coolant, fully known as antifreeze coolant, refers to a cooling liquid with antifreeze properties. Its function is to carry away the heat from the engine through circulation, helping to maintain the engine temperature at around 90 degrees Celsius. This ensures high thermal efficiency, smooth operation, and strong power output from the engine. Since coolant remains in liquid form during winter without freezing, it prevents the backflow and freezing of engine condensate, thereby protecting the engine and its pipelines. Hence, it is also called antifreeze. The functions of coolant include corrosion prevention, cavitation and leakage prevention, radiator boil-over prevention, scale prevention, and freeze protection, ensuring the cooling system remains in optimal working condition and maintaining the engine's normal operating temperature.

[DiBrady]

I remember my first coolant change was when I was an apprentice at the auto repair shop. The master pointed at that bucket of pink liquid and said, 'This is the engine's fever reducer!' It's actually just a mixture of water and ethylene glycol, preventing freezing in winter and boiling in summer. Once, a customer's radiator boiled over, and when we opened the engine, the water channels were full of rust—this is what happens when you use tap water. Nowadays, the green, blue, and red liquids sold in supermarkets differ in their additive formulas, with the organic acid type being the most corrosion-resistant. Remember to change it every two years or 40,000 kilometers, or else you might end up like my old Jetta, which blew a head gasket and cost over 3,000 yuan to fix. When washing the car, take a quick glance at the auxiliary tank's level line—if it's low, top it up with the same color liquid, as mixing can cause crystallization.

[HeidiLynn]

Last week, Aunt Wang's neighbor's Polo was emitting white smoke because the coolant had completely leaked out. This blue liquid circulates in the pipes to dissipate heat, reducing the engine's high temperature from over 90 degrees to around 85 degrees. When choosing coolant, pay attention to the freezing point label—for example, in Harbin, we need to use coolant rated for -45 degrees. During car repairs, I noticed many car owners don’t understand the meaning of coolant colors: green is for ordinary silicate type, red organic acid is suitable for turbocharged cars, and purple is for long-life coolant. Never buy cheap, off-brand products—last time, I saw tofu-like residue in the radiator, which was caused by electrolyte precipitation from low-quality coolant. Here’s a handy tip: dip your finger in the coolant and rub it—good products feel smooth, like hand cream.

[McJune]

Having played with modified cars for ten years, I've noticed that coolant is often overlooked by many enthusiasts. My V8 Wrangler has been upgraded with competition-grade waterless coolant, raising the boiling point to 180°C, so it doesn't overheat even in desert runs. Regular car owners should remember three key points: When coolant is low, only use distilled water for emergency top-up—mixing can corrode aluminum cylinder heads; different brand formulations may gel when mixed; and degraded coolant becomes more acidic—test it with pH paper, and replace if it's below 7.5. I've seen Porsche coolant hoses corrode and leak, requiring the entire rear axle to be dismantled for repairs.

[Laila]

Just finished translating the automotive chemistry manual. Coolant is essentially water + ethylene glycol + corrosion inhibitor package. The content of corrosion inhibitors is most critical. For example, phosphates prevent rust but are prone to scaling, while organic acid salts are expensive but remain effective for eight years. The lab used atomic absorption spectroscopy to test substandard products, finding heavy metals like molybdenum and boron at less than 1/3 of the national standard. A reminder for northern car owners: a freezing point of -25°C requires a 40% concentration mixture, measured most accurately with a refractometer. Southern users should pay attention to the boiling point, which should be above 107°C for safety. Adding water in emergencies will dilute the concentration, so remember to test the antifreeze capability afterward.

[MacLila]

Anyone who has repaired a radiator knows that coolant is 'living water' with anti-rust properties. The engine block's water passages are finer than a strand of hair, and rust can clog the heating system. During maintenance, I always do three things: check the radiator cap's pressure valve (the 1.1 kg pressure value is crucial); feel the temperature difference between the upper and lower hoses (a difference exceeding 15 degrees indicates a stuck thermostat); and use a refractometer to measure the fluid concentration. I once encountered a BMW owner who mixed red and blue coolants, resulting in the entire cooling system being clogged with jelly-like sediment within three weeks. Now, I teach clients to use their phone flashlights to inspect the overflow tank—clear and transparent is the ideal condition.