Why Does the Coolant in the Car Decrease?
3 Answers
The main reason for the decrease is natural evaporation, with normal consumption typically being half a liter per year. Rapid consumption may be caused by leaks or poor circulation, with leaks accounting for about 80% of cases. Coolant Replacement Method: Before completely replacing the coolant, conduct a thorough inspection to check for any signs of leakage or cracks in the pipes, with a particular focus on the five-way water pipe. The five-way pipe is named for its five connection interfaces to various parts, and the coolant is distributed to different sections of the car after flowing through it. If there is any coolant leakage in this part, the hose should be replaced or the connection re-secured as needed. Drain the old coolant, then flush the fluid channels with clean water. Add water to the coolant reservoir and continue filling until water flows continuously through the engine cooling system. Start the engine and let it idle for 3 to 5 minutes to circulate the water. The initial outflow from the reservoir will be slightly pinkish; continue adding water until the outflow is clear. Note: Remember to disconnect the heater hose and drain the water from the heater core. About an hour after draining, add the new coolant through the radiator hose to allow it to flow quickly into the radiator. Then, pour another bottle of coolant into the reservoir until it is nearly full. Start the engine and let it run for about 10 minutes. As the cooling system expels some air, the fluid level will drop slightly. Top up the coolant to the "MAXT" mark on the reservoir.
Last week, I noticed the coolant level in my old Jetta had dropped, and after talking to a mechanic, I learned there are quite a few possible reasons. The main issue is likely a leak—aging hose connections can seep, especially plastic joints that become brittle over time. The radiator’s welds might also slowly leak; pinkish stains on the ground are a strong clue. If no external leaks are found, the problem could be inside the engine, like a blown head gasket allowing coolant to mix with the oil, which would leave a milky residue on the oil cap. Another common cause is a worn-out water pump seal, which may drip near the belt when starting a cold engine. Of course, some daily consumption is normal—heat causes slight evaporation—but losing more than half a cup a month is definitely a problem that needs immediate inspection.
My experience with three cars tells me that abnormal coolant loss is 90% likely due to a system leak. The joints between rubber hoses and metal pipes in the cooling circuit are the most prone to leakage, as rubber hoses tend to harden and crack after about five years. It's also common for the radiator bottom to develop small holes from stone impacts – these tiny leaks are hard to spot. If you smell sweetness when using the car's heater, there's an 80% chance the heater core behind the dashboard is leaking. Additionally, coolant has a boiling point of 130°C. If the cooling fan fails and causes the fluid to boil, it can spray out from the overflow tank, resulting in loss. Pay special attention to the clamps connecting the reservoir and pipes – loose clamps here cause chronic seepage. The most reliable method is having mechanics pressure-test the cooling system during every maintenance check.
