The series II CX has a hot-air mix climate control system.  In this system, hot engine  coolant is always flowing through the heater matrix, located in the air distribution system.   Cabin temperature is regulated by adjusting the amount of air moving through the heater matrix.  This regulation is effected by opening and closing a door in the air handler.  The advantage of this system is that temperature can be adjusted instantaneously, in response to signals from the temperature computer.  The disadvantage of this system is that there is a very hot mass situated next to the flow of cold air from the a/c evaporator.  The cold air will absorb the heat from the walls of the matrix container.  Cold items ALWAYS  absorb heat from anything that is warmer. 

So, one solution is to cut off the flow of hot water through the heater matrix.    The easiest way to do this is to install a valve in the hose leading to the heater matrix.  There are a number of CXs with arrangement.  The 25 Gti had such a valve.

 La Serie II est dotee d'une system
The problem, however, is that the heater matrix circuit is shared by the de-aerator and the oil cooler.  Place a valve in that circuit that closes it completely, and the cooling system will not bleed itself, and the oil will run hotter.
While poking about in a junkyard I came across a Ford explorer with a heater bypass valve with four connections.  Perfect!
Here is a marked up photo of the valve under no-vacuum conditions.    The yellow line shows the position of the valve.

Hot water flows:

  1. from the deaerator
  2. through the valve to the heater,
  3. from the heater back to the valve
  4. through the valve
  5. out to the oil cooler

 
 
Here is a view of the valve installed:
   
Here is the same photo marked for vacuum/closed conditions

Hot water flows:

  1. from the de-aerator
  2. through the valve
  3. out to the oil cooler
Same installation,  but with the valve held shut with a hose clamp.
A close up  of the hose clamp holding the vacuum capsule in the contracted position.
  also, I availed myself of the opportunity to put all new hose clamps in the installation.