I have been using a valve in the bypass line for 26 years now on a raw water cooled application. Yes I do run a bit cold (130 degrees) however I run easy until the temp has come up, after that I run at 2000 RPM's with the Indigo 3-blade.
One thing I do check is when I turn off the A-4 after a long run I switch the ignition back on after about 4-5 minutes and she reads about 140~150 degrees which is approximately what the core of the engine is actually running at. I think the water bypassing the block cools the "thermostat corner of the head" just a bit affecting the reading on the gage when not using a thermostat.
Dave Neptune
1970 E-35MkII original A-4 still "ticking"