RootesRacer
Donation Time
Jarrid, Do you not agree that if the radiator is full when cold, no air space, the coolant WILL expand, and create more pressure than 7 psi and and cause the relief valve in the rad cap to open?
Tom
Not exactly, but I get what you are saying.
The top tank (in the case of SIII to SV) has some volume that the coolant can expand into. Its not much but the thermal expansion of the liquid is not huge.
Ideally the cooling system would have no room for expansion so that it pushes out a little coolant as it gets hot and sucks it back in after it cools.
These cars were not actually designed for closed cooling, though you can make them work.
Any and all coolant pushed out was intended to be lost and at some point the engine would find a pressure equilibrium where in the course of a startup cycle, no coolant is lost.
The earlier cars (SI/II) have an expansion tank which provides about 1/4 liter of expansion which makes them not as good for making a closed cooling system.