| Message |
overflow tube enters the COT at the bottom. Otherwise, unless the tank were completely filled, when the radiator cooled, it would be drawing in air, instead of coolant, back into the system. On top, the fitting must also be open to vent the air pressure and allow fluid to flow freely back and forth into the radiator. Whether you have an open petcock or an elbow fitting at the bottom of the COT is not significant. But, I agree with you that the shape of the bottle suggests the tapered end should be the downside.
_________________________________________________

|
 |