The theory goes that if you move the water through the block and radiator too quickly it doesn't have enough time to conduct heat from the block or conduct heat to the radiator, so you end up overheating eventually.
One of Newton's laws says:
Q[heat transfer] = q A[surface area] = h[average heat xfer coefficient ] A[turface area](T[body] − T∞) = h[average heat xfer coefficient] A[surface area]∆T[temperature differential]
Which comes down to heat transfer (Q) is proportional to the surface area (A) and the temperature differential (∆T). So that means that the higher the temperature differential between the coolant and the surfaces it flows through, the easier it will be able to transmit heat (through conduction and radiation in this situation). This means that the only variable you have to control in a cooling system (without modifying it other than thermostat/restrictor plate versus nothing) is flow volume. With a lower flow volume being more efficient up to the boiling point of the coolant (which is bad for conductivity).
So there is a basic fluid dynamics argument that this can be true.
In reality its much more likely that the vehicles that creep to a steady overheat without a t-stat are either flowing poorly through the radiator at higher water velocities (flow pattern matters A LOT in a hear exchanger) or the water pump is caveating without the additional restriction in the system.
And that's all the physics I can handle for this time in the morning, and about as well as I can handle explaining it.
right Julian :victory: