[embee]

There are 2 basic system schematics used in cars, usually referred to as "hot bottle" and "cold bottle". In summary …………

I would say the majority of cars use a cold bottle, which is the same as most bikes I've come across, like the SV. The mechanism is as has been described, the engine/rad circuit runs full, with a valved cap to allow pressurised hot coolant to expand into the cold bottle and be drawn back into the engine/rad circuit when it cools and contracts, keeping the circuit full.

The hot bottle system, commonly used by VW for example, runs the expansion tank in the pressurised circuit and relies on a compressible air volume to accommodate the expansion. The cap on the rad is usually simply a plug, as described, and the small hose going from there to the bottle is a continuous de-gassing system to keep the rad full of coolant.