"If what you are saying is meant to be true across this whole platform then there is a simple test anyone can do without logging. Shut off your car before it gets to 97c. If what you are saying is true then the lower rad hose will be cold. Anyone can try that, no special tools required."
I am not sure why you didn't just look at my CTS temperature curve.
See the temperature curves above. This is from this morning. I had my hand on the lower radiator hose every minute or so to feel how cold or warm it is.
I warmed up the BMW in my garage. I kept touching the lower radiator hose to verify that it stayed COLD right up until the ECT reached 97.5C. The lower radiator hose remained cold at ECT 97.5C for a few minutes until it started feeling warm and then hot. The CTS temperature corresponded with what I felt. The CTS temperature was below 0C until it started going up after a few minutes of ECT at 97.5C.
"BTW - saw your video on youtube, what you believe to be the DME controlling your thermostat - the flashing LED every couple of secs (while the video shows your motor temp at below 40C) is actually DME maintaining communications with the thermostat - not opening it."
I explained clearly that the flashing LED was when the DME checks to make sure connection is intact to the thermostat. I explained clearly that the DME actually activates the heater when you see the LED stay ON for about 3 seconds or so. This is clearly seen at 13:04 time mark on my youtube video as I had explained. And also, I showed on my temperature curve in an earlier post with arrows when the DME actually activates the thermostat heater. I am not sure why you glossed over this explanation.
"1. The thermostat would not open fully (conventionally) until 105-107C - don't you think that's a little high? (You might have to research how long it takes the wax expansion to actually overcome the spring. Try Stant or IGI - makers of wax motors. - Don't forget the 5C hysteresis function that will keep the tstat open to lower temps from thermal inertia and friction.)"
In fact, it's even more dramatic. The thermostat opens more or less fully by 100-101C. How long does the wax expansion take to overcome the spring? It depends on the temperature gradient. Going from 97C to 100C (if the coolant temperature were to change instantaneously--a theoretical circumstance) takes a few dozen seconds, less than a minute.
"2. Why are lower rad hoses hot before 97C. Hell I've seen them hot at 90C."
This is a good question. Why does YOUR CAR do this? My car does not do this at all. On my car, the radiator hose stays cold until ECT is 97.5C*. (*Caveat: This is unless the MAP thermostat heater had been activated. For this discussion, we are talking about conditions where the MAP heater has not been activated.)
As far as your experiment with the thermostat heater in your video, there are several things that are wrong with it.
First, you do not have the spring in place. This is an error. The wax element needs the spring force pushing against it to work as per specification. You may have seen experiments on the youtube by others who did basically what you have done, and in those instances, the piston actually flies out of the wax housing like a bullet. This goes to show that there may be some vapor pressure that developed (formation of gas) rather than strictly solid-to-liquid phase transformation.
Second, the way you read the temperature with an IR meter is suspect. The correct way of reading the temperature is to suspend the thermostat in a pot of water with controlled temperature.
The fact that you so distrust the hot water thermostat testing method is the core problem why you misunderstand how the thermostat really behaves. There is a nice SAE paper that describes how they test the thermostat wax in lab setting. It is to take 2 pots of water, each at a different temperature. They take the thermostat from 1 pot to the next, and measure the change in the valve opening and also the time it takes. They do it for several temperature gradients, going from colder to hotter, and from hotter to colder.
So to sum up:
1. On my car, the thermostat stays closed until 97C or so, and it even remains closed for a few minutes at that temp. I am not sure why the thermostat behavior is different in your car(s).
2. The thermostat heater is activated (heated) when the 12V signal from the DME lasts about 3 seconds. The pulses (<0.5 second) you see in my LED does not reflect the heater being activated, and I had explained that clearly in my posts.
3. Hot water test is the way to go. You can do what SAE engineers do, get 2 pots of water at 2 different temperatures, and take the thermostat from 1 pot (after it had reached equilibrium with the water temperature) and take it to the second pot and observe the change in the valve opening. You can even use 50:50 coolant to be able to perform tests at temperatures higher than 100C.
Or, you can send me the thermostats with known behavior in the car, and I would be happy to perform this test for you. This test has the potential to solve some of the mysteries you are encountering.
ADDENDUM:
I was looking at the graph of your logs, BMWNorth, and I am noting that the CTS temperature is HIGHER than the ECT temperature at times. Why is this? How can the CTS temperature be HIGHER than the ECT temperature? I do not see that behavior on my graphs. Is it possible that your ECT temperature reading is off?
