@HOTSHOT-III Absolutely spot on information here.
I've not had the thermostat fail on me, but MY GAWD does my DTR run hot. I am not making this up, my Vespa runs cooler than my DTR.
The DTR could seriously benefit from a lower opening thermostat, especially when you tune.
I've removed my thermostat and now the DT runs a cool 60 degrees. But you're absolutely spot on about having pressure at the cylinder head. It is stops pockets of stale gas forming causing hot spots on the cylinder head (promoting knock).