Ok, I'm not a thermo person but I'm sitting next to the cooling system
designer for our formula car and he is confirming what I'm saying.
If you speed up coolant flow, more heat will be taken out of the engine.
For a given airflow through a radiator of fixed size, a certain amount of
heat can be exchanged. If you speed up the coolant flow you need to speed
up the airflow in order to balance the system. So if you speed up coolant
flow in the system without changing anything else then you will start
removing more heat from the engine than you can exchange with the air, and
the car will overheat.
Also, laminar coolant flow is not desirable for a couple of reasons. First,
laminar flow will introduce a temperature gradient into the fluid. The
further the coolant flows through the heat exchanger, the closer the outside
of the coolant gets to air temperature without significantly cooling the
core of the coolant. So the heat exchanger efficiency is lowered. If the
coolant is stirred (turbulent) then the fluid stays one temperature, and
that hot temperature stays in contact with the tubes in the radiator.
Similarly, laminar flow is undesirable in the engine as well, the coolant in
contact with the block gets hotter than the core coolant temperature and you
get localized boiling on the walls of the engine which leads to cavitation
and erosion.
Hope this helps
James Nazarian
71 MGBGT-V8
71 MGB Tourer
87 325es
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