In the absence of flow, the pressure is equal everywhere. Since there is
essentally no flow to the header tank, then I believe the pressure there
will be (nearly) the same as at the radiator. This neglects some pressure
head due to the height difference and possibly some slight Bernoulli effect
of the water flowing past the tube to the remote tank. Even with these
considerations, I would be surprised if you could measure the difference in
pressure at the inlet side of the radiator versus the remote tank.
I think you may be right about the springs in the hoses. The pressure cap
is supposed to allow water to return to the system without much of a vacuum.
I have no spring in my upper radiator hose and have never seen it collapse.
This may depend some on the radiator cap. I have seen the lower radiator
hose collapse when reving the engine. This was probably before the system
got up to operating pressure. In order to get below one atmospher, the
water pump would have to be generating at least twice the cap pressure;
i.e., 30 psi for a 15 psi cap. Sounds kind of high, but not totally
unbelievable. With a 7 psi cap, you would only need 14 psi or so from the
pump, which is a lot easier to believe.
>How about the case where the pressure cap is on the remote header tank?
>I.e. my MkI.
>the reasone that springs are put in hoses is to prevent collapse, but
>during cooling down. With an closed overflow system you want to suck water
>back in the TWO-WAY pressure cap port not collapse the hose and allow it to
>take a set.