"The needle will point to noon at a temp too low to achieve closed loop. I drove for months without closed loop until fall came and I couldn't get cabin heat."
Hmm, I can relate to that, I get 1/4 on cool days and half on warm to hot days. It does have a pre-heater,... a bit of a laugh in Australia and I do not think it has ever been used!

, but I do get cabin warmth at half temp which it will get too even on cold days. I guess that is the benefit of the diesel, they will get hot, just how hot

is the worry.
I guess I will do some searching for this elusive guage fix, but there are other ways, I have an Android HU and I can plug a OBD II in and get info from that on realtime temps including oil and trans.