There should be a hose that fits over that tube, it is an overflow tube. When the reservoir is considered full it should actually only be about 1/2 full, so if you are filling it to the top you are overfilling it. If you look on the side you should find fill level marks one for when the engine is hot and one for when the engine is cold. If it fills up by itself when the engine is hot it may be over heating in which case you would need to have that checked out.


