he third theory is the closest... But I do Beleive that the Viscous Coupling
works like this.... The fluid Is a dilitant fluid. the viscosity is not
affected by heat....see below...  when it is under pressure it acts as a
solid thus tranfering power between the plates and finally driving the front
wheels. This can happen in a matter of mili-seconds. It is along the same
theory of as that of a torque converter that is found in automatics, it only
uses a different liquid and design but the idea is the same.
di*lat*ant (adjective)

First appeared 1885

 : increasing in viscosity and setting to a solid as a result of deformation
by expansion, pressure, or agitation
 .vis*cous (adjective)
First appeared 14th Century

 2 : having or characterized by viscosity <~ flow>
viscosity index (noun)

First appeared 1929

 : an arbitrary number assigned as a measure of the constancy of the
viscosity of a lubricating oil with change of temperature with higher numbers
indicating viscosities that change little with temperature

vis*cos*i*ty (noun), plural -ties

[Middle English viscosite, from Middle French viscosite, from Medieval Latin
viscositat-, viscositas, from Late Latin viscosus viscous]

First appeared 15th Century

 3 : the ratio of the tangential frictional force per unit area to the
velocity gradient perpendicular to the direction of flow of a liquid --
called also coefficient of viscosity