That is a good plan of action
but you have left out:

a) Having instruments to measure the temperatures of air entering and leaving the radiator, and water entering and leaving the radiator. Good quality calibrate-able IR gun AND Thermometer with thin metal probes are worth the money. Lay out a grid of spots to measure on the radiator to take measurements to find potential cold sections that may indicate poor water flow or hot areas indicating poor airflow.

b) Knowing exactly what Brand and Design Thermostat you have and testing that thermostat yourself to see what temperature it starts opening, what temperature it is fully open at. Also decide what bypass holes you should give it. Similarly consider whether you should try a “Balanced Flow” design.

For those posters thinking time in radiator is the same as time in engine block, think again.
Gallons of flow is equal in the two
but internal cross sectional area of the radiator and block are vastly different.
The speed of the internal flows varies greatly. Liquid flow can zip or linger in different block passages but liquid flow speed through radiator tubes ought to be much more consistent even though no side tank design is perfect, there will be “eddies” that keep tube flow from being perfectly equal.
For airflow, the fins are never exactly spaced right, even before bug collisions do their number on the fin gaps.

Never had a problem cooling any of my cars if the system stayed as it came from the factory. The only exception was my race car, built totally by me (long story) the engine I bought, 499 Indy headed McCandless built. Radiator was a VW Sciroco. Temp would climb to over 220-230 degrees after a run (5.60 in the 1/8) had a big fan on the radiator plus the little external motor to turn pump. A buddy gave me the VW factory ran housing setup that was used on that radiator, not expecting it to help I was surprised big time. Idle all day - 160 top, make a run in the heat - 180 top. Factory guys are paid the big bucks to figure this junk out, follow it. AC friend (went to college to study this) told me the higher the radiator temp the faster it will cool, temp deferential I think he said. IMO if you have a factory stock radiator figure out why the engine’s running hot, not why the radiator isn’t cooling.

I will agree to a point with your first statement. However I have had several 22 inch equipped big block cars through the shop that experienced heating issues with new cores in the radiator. Most were under low speed conditions on 75+ degree days. After verifying all was as it should be. I have sent several of these "problem radiators with new cores" to Glen Ray. They came back and the cooling problems magically go away. His explanation is, the efficiency of replacement cores that are being produced today and the majority of them are not equal to what was used back in the day. One customer who had lived with the issue for several years has not experienced an issue in seven or so years since the Glen ray radiator was installed. All measurements were taken with using a
thermocouple probe next as close to the t/stat as possible and laboratory grade meter.

The second statement is dead on the money. I was taught, the factory boys are not stupid and to ask oneself what are you trying to gain by changing something and would that money be better spent elsewhere ? Example: stock vs aftermarket valve covers, air cleaners etc.

one thing about overheating that makes me a little different from most is, at 200 or 210, i am not concerned in the least.
220, if not for too long [like stuck in traffic], makes me notice, but if it cools back to the 200ish range back on the road all is ok.
it also depends on where the reading is coming from and the accuracy of the gauge involved. most gauges are far from accurate, mechanical or electric.
a good IFR gun helps tremendously.
running too cold is bad in my book. in the past i was a "cool" engine advocate, but have since changed my mind and have had very good results running hotter than most.
however, at these temperatures, your cooling system MUST be in top shape or you will have problems.
just my opinion and experience, your mileage will vary.

I agree. Just because a radiator is new doesn't mean it is any good. The Chinese build a lot of junk that looks good but doesn't work. They tend to cut corners on anything that the buyer doesn't see such as the tubing size inside the core. Anytime a person buys aftermarket parts they have to carefully examine them to verify that they will actually work. If the part comes from China it is best to assume that it is crap and work from there rather than assume it is good. Lots of radiator mfgs in the world, some are great, some aren't.

I will tell you what id did. I have a 1972 dart with a mild 440/727. I built it many years ago and used the original to the car 22" 318 radiator and shroud. used a 6 blade flex fan, no thermostat, and the 4 groove pulley that was on the 440 when i got it from the junkyard to build. It NEVER would stay cool. It would take a good while to get hot, but would eventually creep on up to 220 and keep going so i would always have to just shut it off. It would creep up a lot quicker when sitting still and would TRY and drop when moving but would still just keep trying to climb. Couldnt figure it out because if i took the radiator cap off, the coolant was really moving and if i revved it up, the coolant would really flow! I got to looking at radiators and the only one i really was interested in was the 'cold case' brand as it has 2 rows of 1.25 inch tubes! SO, i bought the 22" cold case radiator, used the original shroud again, a stock 7 bladed chrysler fan, a high flow miloden 180 degree thermostat, and a factory 8 bladed pump. Guess what..it does NOT get hot anymore and i love it! It will idle all day long at 180 degrees no matter how miserably hot it is here in TN. and as soon as i start moving, it drops to about 175 degrees. It never even tries to go past 180 ever! After 20 years of dealing with this, i can finally ride around and not have to worry about stopping to let it cool down. This cold case radiator is still only a 22" like the original that was in it but it sure does cool better. i also do believe the thermostat and factory fan helped a lot too.I debated for months on whether to get a 26" or 22" and talked to Chris at cold case and he thought the 22" would do just fine and it is a direct bolt in. Im glad i got the 22" because its all that is needed.
https://www.coldcaseradiators.com/

not reying to start a peeing contest but just state the facts
1: I agree and will say I question the accuracy of any gauge and have found some new BRAND NAME gauges to be way out of whack and normally at the hot end. I have also found that the warmer the motor gets the farther out of range they usually go. Worst i can remember read 260+ at 200 degrees. Typically electric gauges are calibrated at both ends Cold and Hot. But the pivot point is not in the middle. (think off a see saw that does not pivot in the middle.) Poor connections to voltage and ground will affect accuracy

2: IR guns should only be used as an indicator as they need to be calibrated for the surface(s) they are readin.

3: Thermocouples do not lie and are normally accurate to within 2 degrees or better on a calibrated meter. Their accuracy can easily be checked by using Ice water (32 degees, and water, that boils at 212) In addition their response is almost instant.

OK, I may be a little out in left field here, but by chance have you checked total ignition timing?

Too much timing and todays poor quality gas will create heat. You might be surprised how much timing you can get at 1800rpm and no load (full mechanical advance and full vacuum advance). This is especially true if someone advanced the timing to get the car to idle a little better (bigger carb and/or bigger cam).

If you don"t have a timing light handy, just pull the hose off the vacuum advance, plug the hose to eliminate the vacuum leak, then take a drive.

As I said on the first page, ignition timing is on the list. It has a mopar performance distributor which should have the adjustable advance. I believe these are Mallory units and can be improved with a spring change, some are better than others. I have a copy of Mopar Action around here somewhere that goes into detail on dialing one in.

Times whatever on the shroud. And honestly I wouldn't expect to need anything else.

There's only 2 times in the 30 years I've owned it that it ever started getting hot, once when first put together no shroud and poorly tuned. The second was last summer, parked in traffic on fresh blacktop and 100 degrees ambient. It got up to 220 and a few more rpm cooled it right down. 26 inch radiator of unknown application, poorly fitting shroud from unknown application and 5 blade flex fan.

You need to get air over the core at low speed, this is what a shroud is for.

YES SIR !

A little update here, I pulled the pump and it’s an aftermarket aluminum 8 blade. I don’t see any markings on it, anyone recognize it? The vane spread is about 4-3/8”. The radiator is a 3-row, but a few of the tubes are partially blocked. Looks like rust or sand, maybe stop leak. The coolant drained clear.

Oh, and I made the same mistake that I made 20 years ago - the smaller water pump pulley only lines up with the AC crank pulley. So I’ll be keeping the stock non-AC piece.

Doing some welding the other day and dunked the piece in the water tank, got me thinking of what you said. So used the torch to get a piece red hot, dipped it real fast and out, didn’t cool it much, got it red hot again dipped it for 15 seconds and it cooled down to touch. My thoughts are if the water is slow enough it’ll transfer the heat better, it needs time. After heating and dipping a few times that water got hot and it took much longer to cool to touch.

I don't recognize it but it looks like someone pop riveted a flat plate to the impeller so maybe that is a Flow Kooler? I think that is what they used to look like. These days Flow Kooler has a neat looking CNC aluminum impeller design. I don't know how well it works but it sure looks cool.
https://flowkoolerwaterpumps.com/co...r-dodge-plymouth-hemi-hi-flow-water-pump

That's probably a good guess. I'll be switching to a remanned factory pump.

Well I guess there's just some good old scale in the core. Not sure why, the engine was supposedly refreshed about 5 years ago and the rad doesn't look that old at all. I'm only seeing a little here and there but I have to assume that there's more hiding. It looks like the PO was chasing coolant leaks, could a lack of pressure in the system cause scale buildup? Maybe the system was open for a while.

I've been looking at new rads and anything stock looking with a 3 row core is $500 and up. I'm guessing I can get this one rodded out for $100 so that's the route I'm taking. If that still doesn't work then I need to find something with bigger tubes that will do the job. Everything these days is 1/2" tube and 2 row.

Some welder in his garage has just proven the world's thermodynamic experts across all areas and centuries wrong.

What's next? Gonna prove the theory of relativity is false?

Maybe you ought to go read up on how it works and then you'll understand the reason high flow is the key, here's a hint it has little to do with time.

I have done several projects with industrial air to water heat exchangers that are copper/nickel material with a fan (e.g. a giant radiator), and the heat transfer continues to increase with water velocity up to the point the tubes actually start to erode from the turbulence. Turbulent water flow causes mixing and is good for heat transfer. There was a statement on a previous page that each system has an optimum flow point for heat transfer. That's incorrect - you can always increase cooling by increasing flow up to the point of material limitations, pumping cost (friction loss), or other physical limitations. There's no heat transfer coefficient that reverses at some flow condition and causes the heat transfer of the system to decrease.

In the bucket analogy, the heat transfer RATE between the hot part and the water is actually greater when you first immersed it, and that heat transfer RATE between the part and the water decreases as the difference in temperature between them decreases. If you wanted to cool the part even faster, you would have turbulent mixing in the bucket or the water exchanging itself out so there was no temperature rise of the cooling fluid. It's not a comparable analogy to an automotive cooling system, because the hot part isn't continuously generating its own heat either.

Cooling systems go south pretty quickly if there are air leaks so that could be the problem. If it was run with a leak or two then it could have developed some scaling issues. I think the rodding process will cost you more than $100 but you'll just have to check it out. If you have an old time radiator shop in your town you'll be okay. We used to have a couple of old time radiator shops with old guys who would fuss and fiddle with radiators until they were perfect but now they've all been replaced with new shops that just sell you off shore radiators. They don't know how to fix anything, they just charge you $600 for a cheap Chinese piece of garbage. So if you have an old time radiator shop use it while you can.