Re: Thermostats

[Simon Favre <favres@xxxxxxxxxxx>]

Graham re-awoke the thermostat question for "heated" debate.  ;=)

A point someone (Fred?)  brought up before was the ugly prospect of
cavitating the water pump.  With a thermostat removed, the water pump
doesn't see as much restriction to the flow.  This means less back
pressure.  At high RPMs, when the engine is producing the MOST heat, low
back pressure can result in bubbles forming in the turbulent area of the
water pump impeller.  This results in a DRASTIC reduction in pumping
efficiency.  This could explain why some models will overheat with no
thermostat, and why some will overheat at high speed, but do fine
idling.  Different cooling systems may have a greater or lesser tendency
to cavitate the water pump.  Higher RPMs mean the pump is spinning
faster, which aggravates the problem.

Another data point:  Some race motors, for whatever reason, have been
set up to run with no thermostat.  Many of these have to put some sort
of flow restrictor in place to keep from cavitating the pump.  My race
car is like this.  The Fiat 1100 motor in my Formula Junior was set up
quite well to run with no thermostat.  That is, the temperature stays in
a good range under typical racing conditions in the area where it was
built (N. Cal).  The problem with that motor is that it has possibly
the WORST tendency to cavitate the water pump and boil over.  The water
pump draws water out the front of the head!  A simple flow restrictor
eliminated the problem.

------------------------------

End of alfa-digest V7 #131
**************************