Thanks Mark... I think
ok - laymans terms of how it works.
When you start the engine and it is cold the thermostat is closed. At this point all the water is circulating around the engine waterways. It does not circulate into the radiator. This is so that the water gets up to temperature quickly. It needs a certain amount of heat to make the engine run smoother.
Once it hits the temperature rating of the thermostat, the wax in the thermostat expands and opens the thermostat gradually until fully open. When this happens, the water then flow around the system including the radiator. It gets cooled by the air going through the rad and/or by the fan. It then goes back to the engine slightly cooler.
If the water cools to a sufficient degree the thermostat closes again gradually until the water hits the threshold again and the cycle continues.
Because this process happens at a lower temperature on the cooler therms, it rarely gets to the stage where the fans come on for added assistance in cooling (around 96/97C) or even above 85C on track with sustained hard use. (it still gets hot when stationery though)
The result in my case is that the fans are hardly ever on whilst on track now (Previously there were logged to be on quite a bit using delta dash) and average water temperatures are substantially less overall. Because the ECU has inbuilt compensation for high coolant temperatures it retards the ignition if the coolant is too hot, so this has an added performance gain on track and also as it runs cooler it will take slightly more timing (i havent tried this last bit myself as it is beyond my level of daring at the mo)
The water circulates through the modine that exchanges heat with the oil. This modine has two purposes - 1 to help get the oil up to temp quickly if the water is higher in temp than the oil and 2 to cool the oil down if the oil temp is higher than the water.
If the water is on average 7-8C cooler with the new thermostat - this is directly reflected in my experience in the oil temperature with my oil temp gauge and from logging the ECU for water temps.
I ran with a drilled out thermostat after the september ring trip so water was flowing through the rad all the time and water temps on a cruise would not go above 60-65C and took an absolute age to warm the car up - not ideal so I fitted this stat.