Buy an inexpensive Coolant Pressure Tester.
Check to see if it hits and
holds approx. 14-15 pounds.
My car ALWAYS ran cool until it did not.
A very hot day car show procession up to and on the boardwalk at OC NJ and out of nowhere, I was suddenly at the danger zone and moving beyond.........
Radiator Cap was fine, but I had the smallest of leaks on the upper connection of the lower hose. Never left a drop underneath the car, ( must have evaporated near immediately ), but enough to keep the system from pressurizing.
All was fine (170-190) until stressed, then quickly out of control.
Once found, 1 minute to tighten the clamp and all was well again.
That $20.00 tester could save you hours of expensive diagnosis time at any shop.
Keep us posted of your findings or lack thereof.
Marty