OK - so this morning I loaded Blitsie onto the trailer and off to Silverton Radiators in Benoni.....
First - pressure test - 1.5Bar - no drop in pressure.
Was then advised to strip the rad out, and bring it in for more testing, so off home, drain coolant, strip out the rad, back to Silverton Radiators, luckily not too far....
Secondly was a air-pressure test - plugged all the pipes (overflow bottle still attached), add some air pressure, immerse in the water-tank - no bubbles at all.....
Bear in mind the overflow is also in the system at this point, as they use a cap without a spring pressure in it.
Thirdly, they then caustic cleaned it - to get out any calcification in the core - and water-pressure tested it again - no air-bubbles in sight.
They declared the radiator to be completely leak-free - I have to agree with them...
Also, they didn't charge me for the testing...... What a nice place - I will go back there!!
So, we know all the areas it isn't, but not the areas it is causing a problem.....
So Thursday, we ride again.