Hack said:
This is not and can never be true.
You are right, it is not true to a degree. The coolant does cool, but it's not in the radiator long enough to cool the way it should. the water is just continuouly cycling through the radiator. It is cooling, yes, otherwise the temp wouldn't stay at 220 it would rise even higher.
In order for the system to work, the radiator needs to cool at a faster rate than the heat is absorbed from the block.
Obviously this is the case with all radiators but some cool better and faster than others.
If your thermostat is continuously open, the temp will reach an equilibrium and remain at 220 because the radiator is unable to cool it any lower given the amount of heat that is absorbed by the running engine.
Only so much heat will be tranferred from the radiator to the passing air in the time it takes for the coolant to make its way down the radiator. It will cool X amount of degrees and as it makes its way back through the block and heads, that same amount of temp will be gained.
Putting in a lower degree thermostat will not do anything, once you're at operating temp, the thermostat will remain open, just like the 180 degree thermostat is now, and they coolant will just cycle around with no change or drop in coolant temp.
The reason for the thermostat, other than for warm up. is to close off the water from inside the block and preven it from entering the radiator. This allows time for the coolant in the radiator to cool. Once the water temp in the engine reaches 180 degrees the thermostat opens and the hot coolant goes into the radiator. the coolant that was in the radiator enters the block and the thermostat closes. That hot coolant that was in the block now has time to cool in the radiator while the coolant that was in the radiator begins to absorb the heat from the block.
In order for the system to work, your radiator much transfer heat at a faster rate than the coolant in the block absorbs heat, otherwise your thermostat will never close. A higher temp thermostat will delay the time and possibly allow the coolant to cool to a lower temp in the radiator, but at the same time the coolant is staying in the block for a longer period of time. If the radiator is capable of cooling more efficiently than the absorbtion that takes place inside the block, then your temp should drop; if not then your radiator is inadequate and needs replacing.
If that doesn't make sense then please explain where I'm wrong?