Reply to "Why do we need the Radiator tank ???"

Right on Dave.

The tank which the motor outlet hoses connect to is a "swirl tank" its job is to remove air from the coolant. Do you need it? Some race car designers think so, but not all. There's a lot of street cars running around without one. Swirl tanks don't normally have radiator caps, just an air bleed on top plumbed to the "expansion tank". The Pantera's overflow tank looks a lot like an expansion tank, except its not plummed to the suction of the water pump as an expansion tank should be.

Your cars coolant system needs some way for coolant to be relieved as it expands from heat, and to be drawn back into the system as it cools. One method is the familiar overflow tank which is open to atmosphere and connected to the radiator at the radiator cap. As Dave points out, the more common design is now to use an "expansion tank" connected on the suction line between radiator outlet and water pump suction, or connected to the water pump directly at a low pressure (suction) tap. The expansion tank will have a radiator cap and becomes the high point & fill point for the coolant system.

My new cooling system will employ the overflow tank as an expansion tank, I will mount it where the swirl tank is normally mounted, to give the engine compartment a "stock" look. I will not have a swirl tank in my system. There will be 2 air bleeds in the system, one on top of the radiator outlet tank, and one where coolant exits the motor. These bleeds will also be connected to the expansion tank, as Dave has described.

cowboy from hell