Coolant Recovery Non-Pressure System - 2.4L

As the engine warms, the coolant in the closed system expands and builds up pressure against the radiator pressure cap. When pressure, on occasion, exceeds the rated pressure of the cap, the coolant forces the lower seal open and allows the expanded coolant volume to flow into the hose leading to the external coolant bottle. The bottle accepts the expanding fluid. This allows the main circuit to remain full of coolant with no air. Then, when the engine is in an environment where it is transferring less heat, or it is shut off and starts to cool down, the coolant also begins to contract. As it contracts, it begins to create a vacuum in the enclosed space of the radiator cap and filler neck that starts to draw coolant back into the radiator from the external coolant bottle. The coolant flows into the radiator through a bleed hole in the lower area of the radiator pressure cap. This method of operation requires that the bottle have a minimum amount of coolant in it at ambient temperatures, as it would be highly undesirable for the radiator vacuum to suck in air from a depleted coolant bottle.

The advantage of the coolant recovery bottle is cost. The system is much less sophisticated then a pressurized bottle system but puts a premium on a successful coolant fill that contains no air. The coolant bottle cannot be allowed to run dry. If it does, air could be sucked into the system, the water pump could cavitate and the cooling system be destroyed or severely damaged.