ok so, my "new" 89 Wolfsburg has run its temperature up to 3/4's on the gauge consistently and stays there without any other issues.
I have just had the shop replace the thermostat when timing belt was being replaced last week.
Shop confirmed water pump is in perfect running order.
I have replaced the cracked coolant expansion tank, no longer any fractures and no signs of leak.
When burping the coolant system on last top up, the coolant was flowing free and clear.
I cannot seem to get the temp to sit at half the way it sits between 5/8's and 3/4's
My only other thought is that the gauge is just incorrect.
Tomorrow my next step is the Coolant Temperature Sender/Sensor (black)
...could this sensor alone cause this issue? Zero warning lights, no CEL