Me Again

The radiator on my 1943 Oliver 70 RC is a none pressurised type i am told, But when I started it up after sitting for about 14 years the water came out of the filler cap. I can see a pipe in the neck of the Radiator that comes out down the back of the Radiator. I am assuming it is a overflow of some sort, but nothing comes out. How can I tell if this is a pressurised system or non pressurised, and if it is an overflow pipe, surley all the water will come out when hot. Or am I looking at leaking gaskets, as it runs very smoothly.

Regards

Richard