Having spent so much time on the cooling system I had become used to it working perfectly, but on a run during the lockdown it started to misbehave again. On this occasion the engine temperature suddenly went up to 104°C and would not come down. What was odd was that the fan, which is set to come on at 95°C did not come on. And even switching it on manually there was no effect.
My first thought was a stuck thermostat so the first thing to do was to remove it. Running the engine in the garage showed identical symptoms and the expansion bottle was still at the same level as it had always been. So all I could think of was that the coolant was not circulating. That meant either a blockage or a failed water pump.
So first thing was to disconnect a number of the hoses and trying the reverse flush method. Having done that with nothing obvious coming out, I decided to change my filling technique. So instead of filling through the expansion bottle I disconnected the narrow pipe that would originally come from the heater and fitted into the top of the radiator, put a funnel in it and filled the system while the engine was running.
It was quickly obvious that the coolant was now circulating and after quite a few 'burps' from the system it all settled down. So I reconnected the hose and took her out for a run. Result, cooling absolutely perfect 😅
So I have no idea what I did to make it work again. All I can think of is that a large air bubble surrounded the water pump (it a design fault on the T16 engine destined to be fitted with air conditioning that the water pump sits at the top of an inverted 'U") so stopping the circulation.
Have subsequently gone for a few runs and it all behaving perfectly again.