Sorry James, being a forum moderator, I cannot let this go
Quote:
The expansion tank on a dolomite is an expansion tank.
The air in it allows for a cushioning effect on the cooling system allowing it to heat up and cool down without putting undue stress on other seals and components.
The definition of an expansion tank is unambiguous,
it is a vessel outside outside of the pressurised loop of the cooling system,
in other words it is always at atmospheric pressure.
(Said expansion tank is connected to the radiator cap's neck on the header
(whether or not said header is within the radiator or is a separate remote vessel).
If the pressure within the cooling rises to a certain (preset) point the cap will
release coolant into the expansion tank. Upon cooling (and the pressure thereby falling)
the action of the cap will permit coolant to be sucked back into the system.)
A header tank is the highest part of the cooling system,
up until the 60s these were normally incorporated into the top of the radiator.
From the 70s separate remote headers have been employed. These incorporate a cap
and two connections, the bottom being a feed back into the cooling system (usually the bottom
hose but always before the water pump) and a top connection for the bleed from the highest point of the engine
(sometimes there are two top connections if the car has two high points, eg Vauxhall Vectra).
Given that gravity is employed, for best efficiency a header tank should be as high as possible.
The remote headers normally have spare capacity to allow for some expansion of the coolant, thereby negating the need
for an additional expansion tank.
Whether it is remote or integral, a header always has the outlet at the bottom.
thanks,
Ian