Cooling problems

AJ/FormS said
Over 40ish mph is a cooling system problem, assuming adequate ignition timing.
By this speed ram air should have taken over. The shroud and fan are by now out of the picture, and the stat should be running wide open.
So you need to look to the basics;adequate rad exposure to the wind,adequate waterpump rpm, and rad efficiency.
Of course it wouldn't hurt to verify the stat is opening WIDE.
There should be,at 40 mph, a 30 to 50 degree difference in the cooling system temp between the top of the rad and the bottom. Straight water is a better coolant that any ratio of antifreeze. To run it tho, you have to protect the water-pump seal with an additive-package.
Adequate waterpump rpm starts with your engine rpm at the overheat speed. And Adequate engine timing usually includes the VA system. Most SBMopes like 44 to 54 degrees at about 2200 rpm when cruising. I have no idea about 470's but I can't imagine they would be much different.

Tonight when I got home I started with the basics. I pulled the pump belt and made sure the pump spun , Its oem passenger side inlet , spun free . Next since there was no water left I filled the radiator and pulled the drain plug , dumped easy no problem . then I pulled the thermostat put the neck back together filled with water only.
I started it and let it run for about 20 min in park then neutral , drive etc . temp stayed good for about 10 min , between 15o and 180 then the last ten min moved up slowly to 200. I shut it down and took temp readings for what its worth. The radiator 150 , heads were 215, water pump 200. If I had taken it for a run it would have blown again .
Here are a couple pictures of the radiator. Radiator core is 21 1/2 " X 18 1/2" I don't know the size of tubes as I've had this for several years . I'll try and find something on
it. Fan is a 16" fan did the paper trick in front grill fan sucked it up to the grill. I'm thinking a flow issue.

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