What is the function of the coolant reservoir?

[DelOmar]

The engine cooling system is equipped with a coolant reservoir, the main purpose of which is to visually check if the coolant is insufficient and to store coolant. The coolant in the car's cooling system is a type of long-lasting antifreeze and anti-rust coolant. It not only prevents water from freezing but also reduces scale formation, wear on the water pump impeller, and enhances heat dissipation capacity. Below is a detailed introduction: 1. When the coolant temperature rises and its volume expands, the liquid pressure will push open the valve on the radiator, allowing the coolant or steam from the radiator to enter the reservoir through the steam connecting pipe. When the coolant temperature decreases, the pressure inside the radiator drops, and the coolant flows back to the radiator through the intake valve on the radiator cap via the connecting pipe. Additionally, the reservoir has a steam vent pipe at the top cover. If the steam pressure becomes too high, the steam can be released through this vent pipe. When the coolant level in the reservoir drops to the lower mark, it should be replenished promptly up to the upper mark. 2. The coolant level should be checked when the engine is cold. The level should always be between the minimum (MIN) and maximum (MAX) marks on the reservoir. The antifreeze content in the coolant should ensure it remains liquid at low temperatures, and the coolant should also possess anti-corrosion properties and high-temperature stability. To maintain the coolant's performance, it should be replaced every two years, preferably at the beginning of the severe cold season. When replacing the coolant while the engine is hot, wait for 15 minutes after shutdown or until the temperature drops below 100°C. Protect your hands with a cloth and slowly loosen the radiator cap to avoid burns. If more than 1L of coolant needs to be replenished, it indicates significant coolant loss, and the vehicle's cooling circulation system should be inspected.

[Antonio]

I've been driving for years, and the coolant reservoir is a transparent plastic tank that holds engine coolant, primarily to accommodate the thermal expansion and contraction of the engine: when the engine heats up after starting, the liquid expands, and the excess flows back into the reservoir for storage; when the engine cools down after shutting off, the liquid contracts, and the system draws water back from the reservoir to refill it. This ensures the entire cooling system remains full, preventing air from entering, which could cause uneven cooling or overheating. During regular maintenance, I periodically check the fluid level in the reservoir, making sure it stays between the MIN and MAX marks. If the level drops unusually fast, there might be a leak or a sealing issue somewhere, requiring prompt repair. The reservoir is usually located near the engine bay for easy observation without needing to open the cap. During seasonal changes, I also check the coolant color to ensure it hasn’t degraded or formed deposits. It’s recommended to replace the coolant every two years to prevent internal parts from rusting or getting damaged. Though this small component may seem insignificant, it plays a crucial role in ensuring the engine operates properly.

[DeAngelina]

As a car enthusiast, I highly value the practical functions of the coolant reservoir. It buffers system volume changes: when the engine is hot, the expanding liquid is pushed into the reservoir; when cold, the reduced liquid flows back to maintain pressure balance. This prevents cavitation, vapor lock, or localized hot spots that could damage the water pump impeller. During my weekly checks, I always glance at the reservoir level to ensure it's within the normal range—if low, I top it up with fresh coolant. The transparent design of the reservoir provides a clear visual of its condition, with grayish sediment indicating it's time to flush and replace the fluid to prevent rapid corrosion. During maintenance, I also ensure the reservoir's sealing ring is intact, as cracks can lead to leaks and severe overheating. Developing these habits helps extend engine life and prevents sudden high-speed breakdowns.

[DeJasmine]

The coolant reservoir stores excess fluid to accommodate temperature changes: when the engine is hot, expanding liquid flows into the tank; when cold, contracting liquid returns to the system to fill gaps. It maintains a full cooling system to prevent air mixing, which reduces heat dissipation efficiency. I check the reservoir level within the marked range before each drive. Abnormal levels often indicate potential issues requiring investigation. This small tank ensures smooth operation but is easily overlooked.