[TR] Water pumps.

[Randall]

> The

> flow rate of the fluid through the heat exchanger does not affect how much

> heat is transferred.

 

I disagree.  As the fluid cools during it's trip through the exchanger, the
delta-T across the exchanger drops, causing less heat to be transferred.  So
the slower the flow, the more delta-T drops and less heat is transferred. In
the extreme case of no flow at all, the fluid temperature drops until
delta-T is zero and no further heat is transferred.  If this were not true,
the thermostat could not regulate engine temperature.

 

But of course, that says that faster flow can only increase heat transfer
(up to a point), not reduce it.  However, there is another problem that can
arise, and IMO is the root of the old myth about coolant flowing "too fast".

 

The radiator presents a significant restriction to coolant flow, meaning
there is a pressure differential across it when coolant is flowing.  To
increase the flow requires more pressure.  But the pressure cap is on the
high side of the radiator (and is only 4 psi on the earlier TRs).  So, if
the pressure drop across the radiator (aka head) becomes high enough, the
pressure cap will open and release coolant from the system.  Obviously, lack
of coolant results in overheating, but the coolant loss came first.  FWIW,
this problem is mentioned at the bottom of
http://stewartcomponents.com/index.php?route=information/information
<http://stewartcomponents.com/index.php?route=information/information&inform
ation_id=11> &information_id=11

 

A related problem can happen even without coolant loss; namely the low side
pressure goes enough below atmospheric to collapse the return hose (or hoses
for TR2-4A).  I used to own an Oldsmobile V8 that suffered that problem;
which GM had solved by putting a reinforcing spring inside the lower hose.
If you had the wrong hose fitted (ie a generic replacement instead of the GM
specified hose), you could actually see it collapse just by buzzing the
engine to redline.

 

Yet another issue with the early TR motor is the original aneroid type
thermostat.  It relies on a heated gas expanding a bellows to open the
thermostat valve.  But, the bellows is also exposed to pressure from the
water pump, which tends to force it closed.

 

-- Randall

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