
ENGINE COOLING AND VEHICLE HEATING 107
increasing engine speed, until the resisting torque im-
posed upon the fan by its air flow rises to an extent that
overcomes the viscous drag of the silicone fluid and
allows the coupling to slip. Maximum fan speed is
therefore governed by the ultimate slipping action of
the coupling, the latter being predetermined by the
viscosity of the silicone fluid and the degree to which
the coupling is filled.
The more comprehensive temperature-sensitive fan
drive differs from the torque-limiting type in that pro-
vision is made for automatically varying the degree to
which the active part of the coupling is filled. ...