So I have stock Eddy and the gauge used to do the usual symptoms of a failed main thermostat. Basically never getting to 90 and showing as low as 75 on the dial and even lower in the hidden AC value. By the way that latter value is the block water temp.
Replacing the thermostat fixed all these issues. The guage should rise to 90 within about 5 mins and stay there no matter what if all is well. The hidden AC value should show about 85 to 87 and no lower, if it does the thermostat is sluggish and on its way out. My personal experience of course but gives you an idea of what to look for.
