How does the coolant in the resivour enter the system
Its pulled in by vacuum.
Coolant is like anything else, when it gets hot, it expands. This forces coolant out of the radiator, through the little hose that connects to the plastic reservoir, and into the reservoir. When the coolant cools down it contracts, pulling coolant back into the radiator. This is why it's very important to have the radiator filled to the tippy tippy top when the engine is cold. Like from sitting overnight. HTH. -Jim
through the little rubber hose-
The reservoir should never be empty. There is a cold level line and a hot level line. Do as Jim said and fill the radiator to the top when cold and then add fluid to the reservoir cold line.
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