The model of the oscillating molecules can also be well applied to the difference between air and liquids. E,g., the question of why fins are necessary for air-cooling and not for liquid-cooling. The answer is quite simple: In liquids the molecules are much closer together (in water, more than 1000 times closer). This means, that the oscillation energy can be much more intensively exchanged, which is exactly what engine-cooling is all about.
Water also has another special property. It can transport heat very much better than e.g., oil can. This is why the heat from the heating plant in the basement, is always transported into the individual rooms by water, even though the valves in the system would benefit much more if e.g., oil was used. This is why, in hydraulic equipment, one sometimes works with a mixture of oil and water, to be able to ensure the necessary lubrication and still lead the heat off effectively.
This quality is urgently needed in the cooling system, because the amount of water used to cool our ever increasingly powerful engines is constantly decreasing. Six liters in the circulation (including the heating) is a lot nowadays, indeed, there are a number of engines which have less than this amount. Of course, as in all aspects concerning the motor vehicle, weight reduction also plays a part. However, in the motor vehicle, the effectivity of the heat exchanging qualities of water is somewhat curtailed by the large amount of anti-frost which is added, something e.g., that the home-heating doesn't have to bother with.
So, we arrive at the already known result, that alltogether, it's more favourable to transfer the engine-heat to the coolant and then to the ouside air, than it is to guide it around the cylinders so that the heat can be directly transferred. The somewhat greater weight of the water-jackets and the radiator, compared with the sheet-metal for the air-ducting, requires less energy than a fan would need, which blows 10.000 liters and more air per minute around the engine.
Our model of the oscillating molecules, also explains very clearly, that because of the much higher transfer-density, the coolant can cool much more evenly. It's just that there are a few places e.g., where a sufficiently large amount of cooling-air simply cannot reach. And, when the temperature-peaks have been whittled down, the average temperature could very likely, even be increased. 09/13