Well I've done the UV test and as far as I can see there're no leaks in the system. Have done some reasonable journeys and then run the engine until the cylinder head is reading 100degrees, hot enough to pressurise the system and I assume to open the thermostat, but can't be sure.
Notwithstanding my ...

You don't have your window open do you? If it's that I wish my Bongo went fast enough to make a rushing noise!

Hopefully now someone with genuine mechanical knowledge will help you......

Thanks for the info Geoff. I'll report back after the uv is delivered and i've done the test.
I've done some research and came across 'waterless coolant' http://www.evanscoolants.co.uk/Coolants/Automotive/classic_cool_180. Although not cheap, if it lasts for 20 years (longer than me I think) and ...

Had an experience on Monday that I can't explain...... a repeat of an experience 4 years ago.
We took our Petrol V6 to the south coast for a long weekend. 200 miles there absolutely fine. On Monday, after a 20mile run when we got back to base there was a bubbling from under the bonnet. Rather ...