Lost my original thread . . . .

I lost my original thread but I wanted to give an update to my problem.
It was titled "air pump". I want to thank all that replied. My problem
was that I had a knocking sound every time the engine would get hot after a long ride in the very hot weather and the knock would go away when the engine cool'd off.
I have a '90 Grand Marquis for those that hadn't seen the thread. I was going to flush out the coolant and replace with new coolant since the thermostat was new. I went on Saturday to do so. I went to a radiator/air conditioner only shop which is in Coney Island Brooklyn, for those who know the area it is Larry's Radiator.
While examining the radiator before flushing it a crack was found in it. It has a plastic radiator. It was the kind of crack that didn't create a leak but was more like a squashed in crack closing off some of the radiator from operating. Being plastic it could not be soldered and boiled so I replaced it.
The car is running so cool now even in the 90 degree heat and with the a/c on the highest the temp. needle goes is half way. There has been no knocking since I replaced the radiator but I really haven't driven far until today. I am taking a ride to Atlantic City, approx. 120 miles each way and I have a good feeling that the problem has been resolved.
Again, thanks for all the replies.
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Just got home and this thing is driving me nuts. I drove 120 miles this morning averaging 65/70 mph all the way there. Car ran cool. Got there, shut the car, restarted, no knock.
Drove home, same 120 miles, averaging the same speed. Ran into some bumper to bumper traffic near home but temp. gauge stayed in the middle. When I got home, shut down and restarted, _and damn_, the knock was there.
So, after a new water pump, new thermostat, new hoses, radiator and coolant and I still get the knock. Not as much as before but nevertheless it was still there when I got home. Let car cool about 15/20 minutes, knock gone.
I am just about to give up on this thing.
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