Outer Limits 4x4 Board

The lid on my overflow bottle seems to have a 1 way valve in it. I cant blow air through both ways.

It lets water from the rad to the bottle but not the other way around. Do I really need it if all it does is catch coolant?

It would be nice to remove it so I have more space for an airbox.

No its definately required. its an expansion tank.

Without it, when you get hot you dump coolant into the engine bay and when it cools down again it sucks air back into the system

You can see the problem.