2002 overheating AGAIN

I have a 2002 Thunderbird that recently overheated. It had overheated once before several years ago and the problem was a cracked overflow bottle. This time my wife was driving in very hot weather (90 degrees) and in stop and go traffic and the car overheated. My mechanic (not a tbird specialist) tried to reproduce it by running it idle, running in idle with ac on and driving the car around for 15 minutes or so but the temp indicator remained normal slightly below half way. He replaced the thermostat anyway. I just ran the car in idle for about 1/2 hour, 10 minutes of AC on and a few minutes of slightply increased rpm but the gauge was again normal.

I’m concerned about the hydraulic fan failing and my question how does fan failure show itself? Did anything that I or my mechanic did test the fan’s operation meaningfully? I would prefer not to be stranded somewhere if I can avoid it but I realize the risk may be unavoidable. I should mention that I almost never use the car’s air conditioning system.
Since this topic has already been discussed extensively, I merged your post here.

Search the forums for hydraulic fan and you will get your answer. Example:

I have been fighting this cooling system for a while after having to replace the plastic connecting pipe that had disintegrated at 50K, which I found was a common occurrence. Poor design meant taking off the intake to replace it due to the back bolts being about a quarter inch to long. I get this done replace the coolant, burp and I thought I had it beat and the upper radiator hose failed when part of the plastic connector gave out.

Put a new one on yesterday and ran through the "burping" three times and gave up and went to bed last night. It is not a simple system to work on at all and I agree that getting the air out seems to be the trick, but it is not an easy or intuitive task to accomplish.
I had to replace the thermostat housing and since the old one was bad anyway I just broke it up so I could get to the back bolts. Then when I replaced the new one I switched out the bolts for Allen head and a swivel Allen wrench works