I am going to try to keep this short.

I really don't want this to turn into a bickering match about - aluminum vs copper, thermostat vs no thermostat temperature or degree of thermostat to run have read way to much of it.

1972 Scamp 383, 727 trans w/remote cooler, 3.91 gears, electric fuel pump.

To start, bought the car last summer and the dash temp gauge worked, sort of. Normal warm days the gauge would read what i am guessing was about 150. During cooler days it would barely come off of cold which leads me to believe there is no thermostat. Gauge on dash stopped working so installed a phantom temp gauge in it. The instructions tell you to put the ground as close to the sensor as possible, i did not do this due to not wanting extra wires under the hood, but is a good ground. This gauge during same situation on warm day was reading 180. Which was kind of was expected due to dash gauges not being the most accurate.

Forward to last week. 90 outside and went for a drive after about a half hour the temp got up to 205. This is not horrible but i am used to a more efficient cooling system in all the cars i have had in the past. So within about 10-15 degrees of the thermostat. Which would be under under 200 no mater what. Drove 55 mph for about 10 min and temp did not go down. Normally am used to getting up to speed and engine cool off some. Stopped at the store for a few minutes came back out car started fine but had rough idle.

Next day started up the car and let it idle up to temp 180. Broke out the thermal imaging camera and started looking at temps. Temperature of parts of the radiator, upper and lower hose were all the same from cold all the way to 180. So yeah probably no thermostat or is stuck open to partially open. Once it got up to temp coolant started to rise in the radiator and when rev it up coolant level dropped while rpms where up. So seems normal. All the way up to this point i saw no movement in the radiator as far as flow.

I plan on changing the water pump to flowkooler and high flow thermostat have not decided which one yet. What are you guys running for a thermostat? (Brand)

The car has radiator 2949045 1969 C-BODY 26 318 BOTH HTR WITH X51
No idea what x51 is. So here is my concerns on this. First the current radiator is built for 318 not a mild build 383. Inlet and outlet are both on driver side. I have read that unless the radiator is separated in the middle to make a row over and row back this is not to efficient due to the liquid going strait down. I am guessing the factory is not this way. Also someone changed the radiator from a 22 to a 26 at some point and i am guessing made more holes to do so. I am looking for a radiator that will drop right in to where the holes are on the current radiator. Does anyone know what i should be looking for to basically get the same mounting as what is in it. I dont know what cars had what kind of mounting.

I have two options, buy new or recore. Called the place near me and they said a recore would be 600-1000. 600 i am not to worried about but 1000 i am trying to stay away from.

I drive the car mainly on the street.
No it does not have a shroud, i know this would help but with different engine and radiator than the car came with, i have not dug into that yet.
I would like to not remove the radiator until i get all the parts.

Taking thermal image from the front radiator for the most part looks the same. From inside the bay you can see some spots that look cooler. I dont know how much the spinning fan plays a part in that.

Last summer i drove the car for 2 hrs straight at 55 mph and did not puke so that tells me there are not major problems but i didnt know the real temp due to it being the dash gauge but again stayed about the 150 mark.

What is everyone's thoughts?

View attachment 1716133435

Looks to me like most of the tubes in that radiator are restricted except for the far left end.
Hot coolant is entering at the top drivers side and flowing across the top, the down through mostly those few tubes and back across the bottom to the outlet.
That explains both hoses being about the same temperature.

Your description of events and your heat image results both confirm it.