I'm going to second this. If the volume of water going in was matched by what the pump could pull (ie: the ID of the lower radiator hose hooked up directly to a larger vessel or radiator), this wouldn't happen. The lower radiator hose acts as a bellows and collapses under the vacuum of the water pump "over pulling" the source.It's made worse by the restriction of the hard pipe going into the hose, but it does show the effect well. If the lower hose was fed by a 1-3/4" pipe from a large vessel it probably wouldn't be happening.
Here is an end shot of an NOS radiator hose with the spring inside already for my 68:I also read the post a couple of days ago about the spring from In Line Tube. Unable to find a hose with a spring already in it.
and DIFFERENT KINDS of "Stainless Steel" , also .
Good type , better type & True SS . like 309 SS & 304 SS - different types .
I go with 304 SS ; when & if I can find it , for my usage .
I worked in a " SX - EW " plant for 11 years , and around 304 SS everyday .
Our 304 SS stayed in 'cells (vats)' of sulfuric acid 340 days a year ; making
"copper sheets" . . . . tuff stuff .
(Freeport - McMoran Copper & Gold , Bagdad Copper Mine ; SX / EW plant) .
. . jim