The working principle of the car expansion tank
The automotive expansion water tank (also known as the expansion water reservoir) is a crucial component in the engine cooling system. It mainly ensures the normal operation of the engine through three functions: regulating system pressure, accommodating the expansion and contraction of the coolant due to heat and cold, and separating and discharging gases.
Core working principle
Pressure regulation and safety relief: When the coolant expands due to heat, the system pressure increases. When the pressure exceeds 0.12 MPa (approximately 1.2 atmospheres), the steam valve on the expansion water tank cover will automatically open to release some steam into the atmosphere to prevent the system pressure from being too high and causing the pipes or water tank to burst. After cooling, the system pressure decreases, and the air valve will open to suck in air to prevent the formation of a vacuum, avoiding the water pump from sucking dry.
Accommodating changes in coolant volume: During engine operation, as the coolant temperature rises, its volume expands, and the excess coolant flows into the expansion water tank; when the engine is turned off and cooled, the coolant contracts, and the coolant in the expansion water tank will flow back to the main circulation system to achieve automatic coolant replenishment.
Water-gas separation and exhaust: This is an extremely important function. During the operation of the cooling system, steam or air bubbles are produced, which are separated from the coolant through the water-gas separation design. The steam will condense into water in the cooler water tank and flow back to the system, while the air is expelled. This effectively prevents the phenomenon of gas blockage and ensures smooth coolant circulation, avoiding localized overheating of the engine.
Why is it needed?
Prevent "boiling over": By releasing pressure, it avoids the cooling system pressure being too high and causing the coolant to boil and overflow.
Protect the water pump: By separating gases, it prevents the water pump from "air erosion" and extends the pump's lifespan.
Maintain cooling efficiency: By stabilizing pressure and liquid level, it ensures that the cooling system is always in the best working condition.
In simple terms, the expansion water tank is like a "buffer tank" and "exhaust station" for the cooling system. It works silently to ensure that the engine maintains a stable temperature under various working conditions.
The common problems of the expansion water tank are mainly concentrated in the following aspects: failure of the cover, leakage, abnormal internal pressure, and sensor failure. Let me help you clarify them:
Expansion water tank cover failure
This is the most common failure point. The steam valve and air valve inside the cover are responsible for pressure regulation.
Symptoms: Coolant spurting from the cover, engine overheating and even boiling over, coolant flowing out from the pipes causing cracking.
Reasons: Valves cannot open to release pressure normally (such as manufacturing defects, long-term wear, dirt blockage or external force damage).
Expansion water tank leakage
Coolant will seep from the water tank body or connection points.
Symptoms: Cooling fluid traces on the bottom of the water tank or around the ground, continuous decrease in coolant volume, poor engine cooling.
Reasons: Water tank material aging and cracking, loose connection pipes or poor sealing, excessive internal pressure causing weak points to rupture.
Abnormal internal pressure
Failure of the cover or system blockage will cause pressure imbalance.
Symptoms: Coolant spurting, engine overheating, low coolant level warning light on.
Reasons: Cover valve stuck (normally closed or normally open), air blockage in the cooling system.
Liquid level sensor failure (some models are equipped)
The sensor is responsible for monitoring the coolant level and triggering alarms.
Symptoms: Incorrect alarm on the dashboard, inaccurate liquid level display, inability to trigger low-level warning.
Reasons: Damaged sensor pins, float blocked by foreign matter, wiring failure.
Other related problems
Exhaust bolt failure: Some water tanks have leaky or broken exhaust bolts, causing the system to fail to exhaust properly or lose sealing.
Accelerated aging: Using tap water instead of coolant will accelerate the aging of the water tank and cover, as water has a low boiling point and is prone to rust.
Fault impact
If not dealt with in time, it may lead to engine overheating, boiling over, reduced power, increased wear on components, and even mechanical failures such as cylinder seizure.
Brief inspection suggestions:
Visual inspection: Regularly check the appearance of the water tank, connection points, and the ground for coolant traces.
Listen for abnormal sounds: Pay attention to whether there is an abnormal sound of coolant spraying from the cover when starting.
Monitor the instrument panel: Pay attention to whether the water temperature warning light is on.
Professional diagnosis: If you suspect pressure problems or sensor failures, it is recommended to use professional equipment to test system pressure and read fault codes.
If you want to know more, keep reading the other articles on this site!
Please call us if you need such products.
Zhuo Meng Shanghai Auto Co., Ltd. is committed to selling MG&MAXUS auto parts welcome to buy.
