Types of cooling system

[DaveCWK]

On my celica, the cooling system has a spring type radiator cap located directly on the radiator which feeds excess coolant as the system reaches pressure into a separate unpressurised overflow tank, and sucks it back in when the system cools.

I recently worked on a mk6 Fiesta, which had a pressurised expansion tank onto which the pressure/fill cap was located.

I was wondering - why the two different systems? Is one more efficient than the other? It occured to me that the pressurisation of the Fiesta cooling system would be affected by the level in the expansion tank as it essentially acts as an accumulator for the system, whereas the (older) Toyota system contains no air in the pressurised circuit and is entirely dependent on the pressure cap to maintain system pressure.

[stevieturbo]

System is just different, with water at different heights in the system, air bleeds at different heights etc

[99hjhm]

You often get more capacity and expansion space with a pressurised tank.

In a modern car it makes a smaller, cheaper radiator.

[S0 What]

You get the sealed expansion tank when the rad is lower than the highest point of the cooling system, the tank is now the highest point to be able to fill the system fully and let air escape instead of being trapped at the highest point, some engine had bleed valves on the highest hose to do this which is TBH a PITA as they usually snap when undone (mainly french cars IME).