[canehdian]

Internal coolant merge appears to be around 55C (same as ERDTT cutoff).
External rad opens around 82-85 and closes around 75-78. So with an optimum temp of ~75C, you see why ERDTTs 55-65 is not enough to satisfy EMM.

B < C.

I have not measured when the mixing valve closes going the other way. Not sure I really could unless there's a PID for the electric heater temp to compare. (which I don't have)
The best you could do is see that engine coolant temp drops more slowly and electric heat starts up.

 

[canehdian]

Unfortunate you can't see it the other way. The key to sucking all the heat out of the engine block is to know when it is inappropriate to turn the electric heating on during the block cool-down.

I'm not sure how it worked for Ampera, but early volts (11-12) had a slight overlap between electric heat and engine heat in that they could reduce/delay ERDTT by using comfort electric and a low fan speed such that it would keep the coolant just warm enough to not restart the engine.
This was removed in 2013+ and even in comfort mode, the electric heat will not start until the coolant has dropped below the engine supplied threshold. As my picture shows above, electric heat would only be used initially to warm both the electric side and the engine side until they merged at 55C. (my picture was ice cold merging with engine hot, electric heat was off entirely)
Then the computer will not engage electric heat again until the coolant temp drops low enough (engine is off) and presumably the valve has closed again.

 

[canehdian]

Turn off electric heating a few miles short of destination, then you arrive with no 'wasted' heat in either coolant circuit part.

I started doing this last point over last winter.
I have an extremely short commute and it shaves probably 25% off the total energy use on extremely cold days.
Makes no sense to arrive at work with a pool of hot coolant to bleed energy to the parking lot. Better to use it all for me.
I hit 'fan only' about 3-4 mins before I arrive at work or home.

 

[canehdian]

When you have real winter, the AC doesn't run.
If it's warm enough that the AC will run, that's too warm to turn the heat on!

Compressor won't run below freezing or so.
Just blend in outside (cold=dry) air.

Oh, and never use the actual defrost setting.
I just have it on standard auto or foot+window setting. Reduces the times AC comes on vs guarantees it to be on with defrost setting. (If warm enough to compressor to run)