[Doug D]

My Dad has a '75 Fury with the 360. Compared to the 318 in his '72 Charger, it ran hotter. I'm guessing the radiator even when new barely could keep the engine at proper operating temperature. Just my observation.

I'd suspect a scaled up radiator if it overheats or gets hot at low speeds and stay relatively cool at highway speeds. Had those symptoms with a '92 Acclaim 2.5L I had - the gauge would show normal at idle and climb to 3/4 at highway speeds. A new radiator cured it.

 

[Doug D]

The thing is, it pegs out even going down the road with heat on blast. My car has the "heavy duty" factory radiator, but I guess it's just past its expiration date, the insides of it do look pretty skanky, even after a coolant flush additive. Thanks!

That's a sign the radiator simply cannot displace the heat adequately. I meant to say my Dad "had" a 75 Fury back in the day. He sold it long ago and has since passed away. As Bob Lincoln posted, it is also possible the block has scaling that cannot be removed with a flush.

 

[Doug D]

This is a photo of the inside of the radiator... Look screwed?

Definitely appears to show signs of some scaling.

 

[Doug D]

ATF+4 should be fine.