[SpudRider]

As usual, thanks for posting the great information, amigo.

I found the following webpage which describes the operation and design of the Thermo-Bob. This webpage duplicates your information, but adds the missing piece of information I was seeking.

http://www.watt-man.com/uploads/TB_Testing.pdf

The bypass line does not contain a thermostat. The original thermostat is removed, and an automotive thermostat, with a higher opening temperature, is contained within the Thermo-Bob. The bypass line is located upstream of the thermostat in the Thermo-Bob. This bypass line is always open, since it does not contain a thermostat. However, the bypass line is much smaller in diameter than the main radiator line. Therefore, the bypass line is more restrictive, and is mostly bypassed after the thermostat in the Thermo-Bob itself opens.