Re-Re- head temps

["Matthew J Reinhart" <matthew_j_reinhart@spacemail.jhuapl.edu>]

                       Subject:                               Time:5:01 PM
  OFFICE MEMO          Re:Re:  head temps                     Date:11/30/95
RDH wrote "The design, placing the thermostat in the water intake from the
radiator rather than the head outlet leads to rather wide temp swings (and is
downright crinimally stupid and incompetent, in my opinion)."
I disagree.  This is another one of those tradeoffs that can be argued either
way.  As long as the thermostat is not backwards, the sensing side of it is
in the path of mixed coolant entering the water pump, regulating the coolant
temperature going INTO the engine.  On the other hand, putting the thermostat
at the head outlet would regulate the temperature of coolant LEAVING the
engine.  So it would seem that sensing the coolant temperature at the head of
an Audi would naturally read higher than the thermostat set temperature. 
And, this temperature difference would certainly be load dependant since the
coolant temperature must rise as it absorbs varying amounts of heat from the
engine.  If you are seeing what you belive to be an excessive rise in coolant
temperature under full load, there may be some restriction in the block/head,
a bad water pump, or some weird coolant mix problem with inadequate heat
capacity.  I am assuming your radiator is doing its job and the thermostat is
not max'ed out.
I can't honestly think of any real advantage to putting the thermostat at the
intake side except for ensuring it is completely submerged in coolant despite
a possible low coolant situation.  In all likelihood, it was just a
convenient location for the design engineers to put it, and a way to ensure
more Autobahn antifreeze sales when changing thermostats.  :-)
   MJR