Does it overflow around the edge of the lid or around the center bolt? If it's overflowing about the edge it's likely a bad gasket. Without a filter in place the oil will just flow back through the inlet holes instead of being forced up against the gasket.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.