I will see if I can locate one of those auto-bleeders. I've never seen those before. Maybe a few burn-outs will help dislodge stubborn air pockets. It will certainly improve my enjoyment of this task.
My fans have shrouds (they come that way from Flex-a-lite) and good seals against the rad so that should not be the issue. In fact, the shrouds MAY be an issue and I might consider the "Woods Flaps" upgrade, although my problems are at low speeds not, sadly, at "over 150 MPH".
I really wanted to avoid drilling holes in my heads, but if this keeps up, that looks like a good idea.
I haven't tried the Purple Ice, but am using the Norosion which is supposed to help in a similar way (but not in my experience). I am not sure which ground affects the sender, but maybe a "fattie" will help me figure things out.
Mark