Cooling question

How many cores are in your radiator currently? Upgrading to a 4 row will help some. IMO, the greatest help will be using a fan shroud with a high cfm electric fan. Couple that with a high volume aluminum water pump and you should be fine. Also, what temp thermostat are you running? Just a few things to think about.

i tried the "4 core" thing, all it does is transfer heat from one core to the next and next etc. I have noticed more cooling problems with electric fans (mine included) as oppesed to using a belt driven fan(not flex). i personally would go to you local junkyard and get a 3.8L Taurus fan or 94-95 mustang fan(with shroud) and use that.They can be had for about 20-30 bucks and have a 2 speed resistor,on high is 3000 CFM+, but they do draw about 40-50 amps on start up and about 10 running. replace the radiator with a 2 core aluminum,remount the condesor by using "custom" brakets made from strap stock(takes 1/2 hour).

I’m not sure what you mean by OEM flex fan. All of the reasonably modern OEM fans are either plastic or steal, with a fan clutch, but I’m not particularly familiar with the car that you own. If it does have a clutch, that’s the first thing to check. When the car warms up, rev the motor. I should produce a substantial mount of noise and airflow.

If it’s cooling at speed, a radiator may help, but it’s not the main problem. At speed your producing far more heat than at idle, but with a higher amount of airflow. What this indicates is that your radiator is rejecting the heat adequately. If you do decide to go with a new radiator, you can get similar performance to a high core count radiator by choosing one with a high fin density. You also get what you pay for in a radiator. A competent designer optimizes for impingement flow in lieu of laminar flow and does so byway of designed in turbulence. An oil cooler may help, providing that your oil is excessively hot, but if the oil pressure doesn't drop dramatically as the car heats up, it probably won't help much.

An electric fan that is of high quality will always outperform a mechanical fan at idle. The Taurus fan mentioned is one of the better choices and is actually about 3800 cfm. What’s more important is that the blade to open area is near the optimum 50% and the motor has a high peak to average current. The average current being approximately 35A and the peak current 110A. Both the high blade density and high peak to average motor allow the fan to move a large amount of air under actual flow-restricted conditions. Also, the Taurus fan uses a particular Seimens motor that uses a dual commutator in lieu of a dropping resistor. The significance of this is that you can’t power both circuits simultaneously without damaging the motor. An even better choice, if it will fit, is the 18” Lincoln Mark VIII fan, which has the same characteristics, but flows approximately 4500 cfm. I can post the dims if you need them.

If you want to be more accurate in the analyses, get hold of a thermal couple. Measure the water temperature, the ambient temperature, and the radiator air outlet temperature. This will give you a good estimation on cooling improvement with changes to either the fan or radiator. As an example, if your coolant temperature is 210, and your outlet temperature is 160 with an ambient temperature of 60. The heat rise from the atmosphere to the radiator outlet air is 100 degrees, the heat rise from the radiator outlet air to the coolant is 50 degrees The total heat rise is 150 degrees

Doubling the efficiency of the radiator will drop the rise to 100 + 25 degrees, and the car will run at about 185 degrees. Doubling the cfm of the fan will drop the heat rise to 50 + 50 degrees and the car will run at a theoretical (no thermostat) 160. If possible, check also the heat rise (thermostat open) from the top fins to the bottom fins of the radiator, 12 degrees is typical. If it’s substantially higher and you’re confident that you have the correct rotation water pump installed, then check and make sure the ignition timing is correct

How old is your current radiator? Possibly just replacing it could take care of the problem.

Another thing to consider is that a new, tight engine will run hotter than an old, worn one. Just the way it is. That is especially true the first few weeks or months.

9 or 10 years ago when I rebuilt my straight six it ran hot. It ran hot for the first few months. I bought a new radiator. Well it turns out I didn't need it. By the time I made the decision to buy the radiator and received it, the car was fine. Now I'm still running the old radiator.

Something to think about.

It's not clear to me what type of fan you're currently using, but you say you used to run a 14" pusher fan. If thta's what you're running now that is part of the problem. Unless space is a big problem (which it shouldn't be with a small block in an early Mustang) never run a pusher fan. They block the radiator and cause the overheating they are supposed to prevent. Look at any stock vehicle with an electric fan, you won't find one with a front mounted fan anywhere. The engineers that design cars know that you simply can't put anything in front of the radiator core, but we as a group have been a little slow to pick up on that principle. There are ways to make pushers work in space limiting applications, and that is to run a pair of small diameter fans as high on the radiator as you can.

Yes, just hang it in the air behind the radiator or fan, I'm pretty well convinced that the radiator is fine, but you can at least make a valid decision once you have the numbers.

Your last post gave the best clue though, I would bet that the air is just circulating from the back to the front of the radiator with the hood closed. Try putting a towel across the top radiator support and see if you get the same 30 degree drop. I don't know if you have orchard supply hardware where you're at, but they sell a thick adhesive backed foam that I've tested to 212F

If the motor is at normal temps when you are driving (25mph or over), then the radiator is doing its job. If it is overheating at idle, then either there is not enough air being pulled through the radiator from the fan or as said above you have hot air circulating back in front of the radiator either through the top of the support or through the radiator itself. What kind of cfm did you measure with the flex fan, just out of curiosity? My suggestion would be to get a SPAL fan and mount it with the stock shroud in place.