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1966 Mustang overheating

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I have a 1966 Mustang with a 302 '68 V8 engine and it overheats.  The car has a high volume Edelbrock Aluminum pump, with a double rolling timing chain,  4 row aluminum radiator from summit, electric fan 16 pull.  The car was sitting for a few years before I bought it.  It has some aftermarket parts for example Unilite Mallory distributor, a Holley 4barrel carburator.  I took the water pump off and it seems to be good but I'm not sure, my friend the mechanic says it's good because it's pumping water.  So then I put it back on and I took the radiator out and flushed it with water and I put it back and the overheating continued.  you drive it like 20 mins and it starts to overheat.  Then I took the heads and took them to a machine shop to be inspected and they were fine so I put them back on with new gaskets everywhere and they were correctly installed.  Seems like the engine is really clean in the inside, like somebody worked in it before, which I like it. It has Shelby springs in the valves.  Took the radiator out again because the top hose was getting stiff like before then I took it to a radiator shop and they flushed it, put it back on and refilled the radiator with anti-freeze and it went down better.  I saw the difference in the temperature, I took it for a drive a few times, short trips and when I got back home the temperature was at like 3/4 between the cold and hot.  When it cooled off I took the top off  the radiator and there were residuals (like tiny rocks/sand) like before I flushed it, then I disconnected the hosed and flushed it again with the water hose, put it back on and it was working at some point satisfactory and after a few short trips it started to overheat again.  Lastly I took it to Jiffy Lube and they flushed it, I thought it was going to work but it made it worse, like in the beginning.

Any advise on how I can fix this?  Do I need a new radiator because it didn't move for so long, or a mechanic fan versus electric fan?  Or because the top hose is getting so stiff, do I need a new water pump even though my mechanic says it's good?

Thank You!!

I would start at the easiest route and try a different thermostat , also what is the idle speed of engine . Had a 93 T-bird that would run hot constantly did all the usual checks ,but over looked one minor detail that the idle speed was a tad bit high and  the water was circulating to fast to cool down , i would also check to see that the electric fan is actually coming on at the right temp

and when you say overheating are you relying on the gauges alone (Which could have a bad sending unit or ground) or is it puking coolant?

50-50 mix of water antifreeze cools better than straight antifreeze

You say that your top radiator hose was getting stiff.  Do you, by chance, have a large spring in the lower hose?  If you don't it may be collapsing, which will restrict water flow through your engine and radiator

If you don't already have one, look into a fan shroud.



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