Manual or Machine Replacement of Coolant?
3 Answers
Manual replacement of coolant is more convenient. Manual replacement allows for thorough inspection and replacement. Method for replacing coolant: Before completely replacing the coolant, conduct a comprehensive inspection to check for any signs of leakage or cracks in the pipes, with particular attention to the five-way water pipe. The five-way pipe is named for its five connecting interfaces to various parts, and the coolant flows through the five-way pipe before being distributed to different parts of the car to function. If there is any leakage of coolant in this section, replace the water pipe or re-secure the interface as needed. Drain the old coolant and then flush the liquid channels with clean water. Add clean water to the coolant reservoir, then continue to fill the reservoir with water so that it flows continuously through the engine cooling system. Start the engine and let it idle for 3 to 5 minutes to circulate the water. The water initially flowing out of the reservoir will be slightly pinkish; continue adding clean water until clear water flows out. Note: Remember to remove the heater hose and drain the water from the heater core. After about an hour of draining, add the new coolant through the radiator hose, which allows the coolant to flow quickly into the radiator. Then add another bucket of coolant to the coolant reservoir until it is nearly full. Start the engine and let it run for about 10 minutes. At this point, the coolant level will drop slightly as some air is expelled from the cooling system. Add more coolant until the level reaches the "MAXT" mark on the reservoir.
I've changed the coolant myself over a dozen times, and doing it manually is actually quite simple: first, unscrew the drain valve or lower hose, let the old fluid drain completely, then flush the system with clean water twice, and finally pour in the new coolant. However, there's always about 500 milliliters of old fluid left in the nooks and crannies of the radiator. For example, the rust residue in my old car directly clogged the heater core. Last week, I saw a specialized coolant exchange machine at the repair shop. It uses two tubes inserted into the coolant reservoir, and the machine cycles for ten minutes to extract every last drop of the old fluid, eliminating the need to bleed air from the system. However, using the machine costs an extra 200 yuan. For regular new cars, manual replacement is completely sufficient, but for cars older than five years, it's advisable to spend the extra money—especially for German cars with cylinder sleeve heaters, as residual old fluid can boil and corrode the water passages.
Just helped my neighbor deal with an overheating radiator, so I've researched this recently. The traditional gravity drain method is the most cost-effective for regular cars—street shops charge around 200 yuan—but it always leaves about 10% of the old coolant mixed with the new. Mixing different colors like green and red antifreeze can even cause jelly-like coagulation. Auto repair shops use vacuum coolant exchangers that extract up to 98% of old fluid, which is especially crucial for aluminum engines—residual acidic coolant can corrode the block. Last time, I saw a mechanic fully open the valves by setting the AC and heater to maximum when replacing coolant in a BMW for a thorough flush. Actually, more expensive antifreeze isn't necessarily better—the key is matching your vehicle manual's required freezing point and anti-corrosion standards. Mixing different brands often leads to foam formation.
