Be sure whatever you use has the hose at the bottom of the container. If it just dumps the excess coolant into the container at the top, It's just a recovery tank that keeps the coolant from spilling on the ground and won't draw it back into the radiator as the engine cools.
For a reservoir to work properly, the overflow hose has to withdraw the coolant from the bottom of the container. The radiator should be filled to the very top of the filler neck without leaving an air pocket in the upper radiator tank.
