What is the reason for the newly replaced coolant losing half its volume in 3 days?
3 Answers
The reasons for the newly replaced coolant losing half its volume in 3 days are as follows: Air in the pipes: There may be air in the coolant pipes. After the car is driven, the coolant circulates, expelling this air, which results in a relative drop in the coolant level. Cylinder component issues: Possible causes include damaged cylinder gaskets, poor flatness of the joint surface between the cylinder head and cylinder block, warping, or loose cylinder head fastening bolts. These issues can allow high-temperature and high-pressure gases from the cylinder to enter the cooling system, leading to excessive coolant consumption. To prevent this, regularly inspect all seals and connections to ensure their tightness. Coolant replacement cycle: Vehicle coolant generally needs to be replaced every 2 years or 40,000 kilometers. This is only a reference cycle. For commercial vehicles with longer mileage, the replacement cycle is shorter. Since driving conditions vary for each vehicle, the replacement should be based on actual usage. Check the coolant's condition, and if it is found to be insufficient, replenish it promptly. If suspended particles, sediment, or signs of deterioration or discoloration are observed, replace the coolant and clean the system immediately. How to choose coolant: The basic indicators of coolant are its freezing and boiling points. Available in the market are coolants with freezing points of -15°C, -25°C, -30°C, -40°C, etc. Generally, it is advisable to choose a coolant with a freezing point at least 10°C lower than the lowest temperature in your region.
I've seen many cases like this where the coolant level drops by half in just three days, and 90% of the time it's due to a leak. After replacing the coolant, the pressure in the system changes, and those aging hose connections, radiator welds, or heater core seals are most likely to reveal their flaws. You'd better use a flashlight to inspect along the coolant lines when the engine is cold, focusing on areas like below the water pump and the corners of the radiator for pink crystalline stains. Sometimes, the seal on the overflow tank cap isn't tight, and liquid may spray out under high temperature, creating a false impression. Also, check if the inside of the underbody shield is damp—leaks at the rear of the engine are the hardest to spot. The worst scenario is a blown head gasket, where coolant can mix with the engine oil. If you find milky white emulsification under the oil cap, it must be repaired immediately. Such urgent leaks must be addressed right away—once the temperature warning light comes on, it's too late.
Last year, I had the same issue with my car. I always found the coolant reservoir level dangerously low in the morning. It turned out that when the coolant was replaced, the mechanic didn’t properly bleed the air from the system, causing the fluid level to drop sharply in the first few days as the air escaped. However, your situation seems more complicated—losing half the coolant in three days is extreme. After parking at night, place a piece of cardboard under the car to check for leaks in the morning. While the engine is warm, squeeze the rubber hoses to see if they bulge, and check if the factory clamps are tight. In some older cars, the heater core’s metal pipes can rust through, leaking coolant under the floor mats. Most importantly, verify if the new coolant is the correct type—low-quality coolant with a low boiling point can evaporate under high temperatures. If you can’t find the leak, take it to a shop for a pressure test.
