I'm not sure about the hose collapsing...I suppose that could be it. I'll see if I can find a hose with a spring in it or check that mine does.
The A/C on or off doesn't make a huge difference, though when I start up a hill, I will usually turn off the A/C ...having it running will make it run just a little bit hotter.
I haven't replaced the coolant since the radiator was replaced a few years ago. When I take off the radiator cap with the motor cold, I can see the coolant right at the top...looks brand new.
I'm not sure what the heck. I will check the lower hose to see if it's collapsing or at least does or does not have a spring in it.
Thanks for the advice!! I'll report back.
I haven't done any flushing of the radiator because we had the radiator completely replaced several year ago because of a small leak. Replacing the radiator didn't change the problem at all.