I bought and used aluminum radiator for my old Duster, it worked fine for the first summer at 160F to 165 F at road speeds above 70 MPH with 4.10 gears and 315x60x15 M/T ET street radials, the next spring it was running above 210 in the spring with the same conditions
I called a radiator shop that I trusted and they said bring it in, they must have clean it or something else that made it work fine again for that summer and fall. The next year the same thing, my message is some aluminum radiators must corrode or cake up inside when sitting during the winter up here I use a good brand of antifreeze(good too -40F) and I think I added a water pump lube and rust preventer in with the anti freeze.
I did the garden hose test in the top inlet with the radiator cap on and the bottom outlet opened and it flowed all the water my 5/8 garden hose would flow into it at full blast
Maybe someone on here knows a good aluminum radiator cleaner to use to flush them out that will help them cool better