Reasons for Frequent Coolant Loss in the Expansion Tank Without Overheating

[JuliannaLee]

The reasons for frequent coolant loss in the expansion tank without overheating are: 1. There is a leak in the cooling system; 2. The coolant temperature may be too high; 3. The water pump is seized; 4. The cylinder head gasket is blown. The functions of the radiator are: 1. To improve the cooling efficiency of the coolant; 2. To prevent the engine from overheating. Precautions when using the radiator: 1. Prevent the car radiator from overheating; 2. Replace the coolant regularly; 3. Do not use tap water as a substitute for coolant; 4. Choose high-quality diluted water when selecting radiator fluid or antifreeze; 5. Perform regular anti-rust treatment for the radiator; 6. Address radiator issues promptly to avoid further damage from continued use.

[DelSerenity]

I've been in auto repair for over a decade and often encounter situations where the auxiliary water tank keeps losing water but the temperature remains normal. The most common cause is minor leaks in the cooling system, such as loose hose connections or radiator cracks, where water slowly seeps out without significant leakage, keeping the temperature gauge stable. Another possibility is a faulty cylinder head gasket, allowing coolant to leak into the engine or exhaust pipe—this needs immediate repair to prevent engine damage. Sometimes, it's due to aging water pump seals or an unsealed auxiliary tank cap, causing evaporation under high pressure. In such cases, it's best to conduct a pressure test and have a professional shop locate the leak—don't delay to avoid minor issues turning into major repairs. Regular maintenance should include checking hose connections and radiator condition, as prevention is always more cost-effective.

[LaSimon]

I've been using this car for five years, and the auxiliary tank always lacks water, but the temperature is fine, which makes me quite worried. At first, I thought it was normal consumption, but after adding coolant several times, it still kept decreasing. Later, when I went for a check-up, the mechanic said there was a small leak at the water pump, causing water to drip away slowly and not noticeably. A friend of mine had a similar issue where the engine's cylinder head gasket was corroded, and the coolant was being sucked into the combustion chamber, with white smoke from the exhaust pipe being a telltale sign. I suggest you check under the car for any dripping traces or pinkish coolant stains on the ground when parked. Also, avoid adding tap water, as it can corrode the system. Try switching to proper coolant, and if that doesn’t work, repairs will be necessary. Before each start, take a quick glance at the auxiliary tank's water level—it's simple and gives peace of mind.

[DiMaci]

As a female driver who drives every day, I pay attention to the issue of the auxiliary water tank. Low water level but no overheating could indicate aging or loose pipe connections, or tiny cracks in the auxiliary tank itself, causing coolant to slowly evaporate or leak. Another common issue is a poorly sealed radiator gasket, which may overflow under high water pressure. Simple check: Observe the water level when the engine is cold. If it drops quickly, watch for leaks. Don’t ignore it, as prolonged neglect can lead to cylinder scoring. Top up the coolant promptly and choose a compatible coolant to avoid mixing. During regular car washes, check underneath for wet spots—it’s convenient and reduces the risk of malfunctions.