Practically Classics Forum

I'm going that route with the rad cap. But I noticed tonight some steam rising from the cap area. Not sure if it's leaking or venting. I'll be having a look tomorrow when it's cool again

Problem solved neither rad or cap but poorly sealing hose weeping steadily but not obviously. Hence steam. Over a longer time coolant evaporates leaving level low and air in system. Not boiling but blowing air

I think we may have a result

Fingers crossed

Hope you sorted you problem. I had something similar happen to my Dolomite 1850 when I fitted the wrong expansion bottle cap. It was rated for too high a pressure, so wasn't venting any air. Coolant boils at a lower temp when you put in under pressure.

Welcome to the forum.
Cooling problems are always a pain in the bum.
Water boils at a higher temperature the higher the pressure it is at so you would probably experience leaks, possibly blown hoses if you go too high.