Quote:
Originally Posted by me and my metro
Correct, a thermostat is also used as flow control in a cooling system. Sometimes cars overheat due to the coolant not staying in the radiator long enough to transfer heat.
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That is incorrect, a higher flow rate will always equal more effective cooling.
With all else being equal. This is basic thermodynamics. Looking at the other side of that statement, the coolant stays in the block a shorter amount of time and picks up less heat as well, meaning it does not need to stay in the radiator as long to dissipate heat since it didn't pick up as much. The problem is that everything else is not necessarily equal without a thermostat.
For example, depending on the vehicle, there is likely a bypass hole behind the thermostat to allow coolant flow through the block while the thermostat is closed to prevent hot spots and allow for even warmup. The disc on the back of the thermostat pushes against that hole in the block to seal it off when it opens, forcing all coolant to flow through the radiator and not allowing hot coolant to recirculate into the block without flowing through the radiator first. If hot coolant is bypassing the radiator and recirculating directly back into the block, cooling efficiency will suffer.
Another problem someone may run into when running no thermostat is that there may not be enough pressure in the block to keep the coolant from boiling at hot spots such as around the cylinders. If the thermostat is located at the upper radiator hose, it creates backpressure in the block as the water pump tries to push coolant through it since it is a restriction even when fully open. The backpressure raises the boiling point of the coolant in the block, preventing it from boiling. If it boils, cooling efficiency will drop dramatically and damage may result.
Finally, depending on the design of the water pump, it may cavitate and lose effectiveness without backpressure. If the pump cavitates and loses effectiveness this will result in overheating because the coolant won't flow through the system fast enough to keep the engine cool. Again, the overheating would be caused by inadequate flow, not too much flow.
When people remove their thermostat and have overheating problems without a good understanding of thermodynamics and how the cooling system works, they often incorrectly jump to the conclusion that the overheating is caused by too much flow through the radiator without realizing the other variables that they are changing. If more flow through the system resulted in worse cooling, truck engines and other heavy duty vehicles wouldn't come with higher flow water pumps than lighter duty vehicles.