"Note: on Japanese heavy tank cooling systems
The Type 2604 tank has two 12-cylinder liquid cooled BMW engines. The cooling system includes three sections of cooling pipe radiators for each engine, and one section of an oil radiator, cooled with two intake fans that draw their power from the main reductor. The air is sucked in through grilles located above the engine compartment , goes through a section of radiators in the air-tight hull, and is released through a grille in the rear of the tank. For engine maintenance, each of the radiator sections opens upwards if the engine compartment cover is removed.
Advantages of this layout include protection from incendiary fluid. A disadvantage is the inefficient use of space.
The Type 2605 layout differs from the Type 2604. It is 35% smaller, but retains the same type of engine, resulting in a very cramped cooler design. Four radiator blocks are shifted towards the rear, and, along with the separate oil cooler, are cooled with one many-bladed fan, connected to the main reductor by a crankshaft, passing between engines. Air is gathered through vertical grilles in the engine compartment, passes through vertical radiators, and is released behind the tank. If the fan breaks, the air will be partially circulated with exhaust fumes, achieved by a nozzle collector on each engine.
Advantages of this design include an efficient use of the space available, and the simplicity of design and adjustment of the large (950 mm diameter) fan. Disadvantages include a lack of air flow over the engine components, leading to overheating of the generator and main reductor, and a small amount of radiator sections (only 4).
The wooden O-I model uses a liquid cooled Daimler-Benz 12-cylinder diesel engine instead of two BMW gasoline engines. The model has two six-section radiators with an air flow achieved by exhaust fumes. The air is gathered by the engine compartment cover. An auxiliary fan helps guides airflow over the engine and helps in clearing out the fighting compartment, driven by the fuel pump motor.
Advantages of this layout include simplicity of design and good ventilation of the tank turret, but only while the engine is running. A disadvantage of this layout is that service of the engine requires removing the airtight radiator sections.