Hopper-cooling is more than adequate for a huge variety of engines. Yet as engine size and engine work load increases, the temperature generated by an engine tends to increase, to the point hopper-cooling is no longer effective. The problem with hopper-cooling is mostly one of limited circulation, leading to hot spots in the cooling jacket. Tank-cooling is an option, but tank-cooled engines are typically setup on a thermosiphon, so they tend to feature large water tanks to encourage flow, limiting their portability.
Screen-cooling, on the other hand, doesn’t require near as much water volume as tank-cooling to be effective. As the cooling water washes over a screen (hence the name), heat bound up in the water is rapidly carried off by surrounding air. With the aid of a pump circulating the water through the engine, screen-cooling is very effective. The only downside to screen-cooling is the added complexity of a pump and, especially if the engine’s really working, the need to more closely monitor the coolant as screen-cooled engines have a high evaporative loss.
Read about Lyle Dumont’s collection in Mogul Engines: The Whole Line.
