W221 S300 S350 Car expansion tank VOLLSUN Brand 2215000649

The coolant expansion tank, also known as the coolant reservoir or degas bottle, is an integral component of the engine’s pressurized closed-loop cooling system. It serves multiple critical functions simultaneously: accommodating coolant thermal expansion and contraction as engine temperature cycles between cold-start ambient and full-load operating conditions, maintaining proper system pressure through the integrated pressure cap’s calibrated spring-loaded valve, separating entrained air and combustion gases from the coolant through its internal degas function to prevent air pocket formation, and providing a convenient fill and level-check point for coolant maintenance. Manufactured from high-temperature PP engineering plastic with excellent long-term chemical resistance to ethylene glycol-based coolants and anti-corrosion additives, the tank is engineered to withstand sustained operating pressures up to 1.4-2.0 bar and temperatures exceeding 130°C without cracking, deformation, or seam leakage. A properly functioning expansion tank prevents gradual coolant loss, eliminates air pocket formation that can cause localized cylinder head hot spots and warpage, and ensures consistent cooling system performance across all driving conditions from winter cold starts to summer highway cruising with air conditioning.