Heinz, I would award you ten out of ten for finding and posting that page of info on cooling. Being a simple chap, I do like things explained in simple words..
The page it`s self only gets nine out of ten... As it does not provide information on the different rad cap types, or the all important correct positioning within the systems of the different type of rad caps, which in the case of Morgans such as mine with possible interchangeability in terms of my two different types of caps, fitting both the rad and the expansion tank, and which if swapped round would cause issues..
The web page also introduced yet another type of remote tank in the form of a catch tank, which I suspect might only be a required fitment to vehicles intended to race on a track, whereby spillage on the track surface seems best avoided, perhaps more so if that spillage might be caused by a blown gasket that allows oil to mix with the water to be expelled from the cooling system, and might cause issues for other competitors...?
As it seems unlikely that Morgans might have been fitted with open type pressure caps, or recovery tanks (?) there seems to be little point in discussing them here, though in general I do have interest in acquiring a fuller understanding on the design and operation of such systems.
Radiator Caps Explained (coolcatcorp.com)
As for much later systems with plastic expansion tank caps as fitted to some vehicles, I suspect without a tube to safely carry off expelled coolant/steam...these caps may be constructed with thermal or pressure activated components within which prevent the cap from being removed while the system is under pressure, in that while the cap can be rotated the linkage between the cap`s top and it`s internal threads connecting it to the tank, are disengaged, only re-engaging once the pressure or temperature has dropped, allowing the cap to then be removed...?.
