I am bringing the car in early Monday morning. I fear that you are correct in your diagnostic. The water vapor is a large concern but it has been doing it for a very long time and is not consistent.
I observed for hours today and most of the time there was no obvious sign of vapor. I think that I am just wishing. I believe that the water pump is bad as well.
There would have had to been clouds coming from the exhaust to lose enough water to cause the over heat alone.
My guess is that the pump is not strong enough to "fill" the top radiator hose and air remains in it and also in other areas of the system because there is not enough force to properly bleed the system.
The volume is OK at idle but cannot provide the cooling needed under load and higher RPM.
I will have the answer on Monday evening so if anyone wants to hazard a guess, it might fun to see who is right.
I think I have provided all the information needed.
It may be a number of things. I have no record of any work on the cooing system.
It is the inability to bleed the system which has me perplexed. Hours and hours of bubbles!
Is air being sucked in through the head gasket?
I just drove it 3 miles , non highway, to my house. It was still warm from earlier and ran very normal with the needle at 1/2.