The tank should be used to top up and should be connected to the outlet beneath the rad cap. It should also have an overflow pipe.

Under normal driving the expansion tank just receives water at high temperature and then that is drawn back into the system when required. I don't suppose you would have a problem under most conditions but it should be connected and kept topped to the max . At the moment if the pressure is released by the cap stat the water will just run off the rad wheras it should go into the tank.

It is only a length of quite small overflow hose and should be easy to buy and cheap.

|OLDMINIMAN

There are 2 RADs used on Sportraks, a long and a short neck version.
(Left and right refers to looking from the front of the engine)

The short neck has 4 pipes. the top hose, the bottom hose , a small pipe from the top tank to the front left of the engine and the pipe from above the cap seal to the expansion tank.

The long neck again has 4 pipes but instead of a small outlet in the top tank it has one low down on the long neck which is below the cap seal and goes again to the left front of the engine. Again there is the one for the expansion tank above the rad cap seal.

My theory is that the small pipe which flows all the time and goes to the front left of the engine heats the inlet manifold to prevent excessive fuel use on cold start. A lot of Mini's had water heated inlet manifolds.

It is likely that your cap may never have reached the pressure required to allow water into the expansion tank(if it were connected)but which ever Rad you have, will have, an outlet beneath the cap above the seal of the Cap and this is for expansion purposes and should be connected to the tank.

I hope this resolves you question

OLDMINIMAN