The fan does not cool anything after 25 MPH. unless you are using power for a while on a hill at slower speeds. Neither does the shroud. My cars that had electric fans on a thermostat would only come on at slow speeds in traffic or at a stop. The performance cars had clutch fans which would help performance on acceleration.
The newer clutch fans had a thermostat built in and would be controlled by hot air coming through the rad.. On a long pull. You would here them activate when needed.
My diesel trucks have a electric activated fan by the ECM that work off of the thermostat in the coolant system. I would need to be pulling a long hill with a lot of weight before you would ever hear the fan kick in.
Shrouds are good to have for slow speed traffic and at idle. Once the vehicle is moving a speed you don't need a fan or a shroud unless the power being made exceeds the cooling of the speed you are traveling with the proper radiator for the HP you are making.
When you buy a radiator for a car you buy them by HP rating. If you have a wide radiator you may need twin fans to cover core. This will use the whole core for the fans to cool your motor until the speed over comes the draw of the fans. Then they would shut off. How often do you hear your fan come on in your new car? Only when it idles standing still for a period of time depending on the coolant flow.
Again the mopar pumps work the opposite of what they appear. The more the blades the less they cool at higher RPM's/speed. AC cars come with more blades on the pump. 340 cars came with less blades without AC for better cooling at Higher RPMs. with the greater HP. They cool better.
I have seen this from years of switching motors in cars from one extreme to another. If I would see the temp rising Traveling at high speed with 391's / 410's in my cars it was an indication of the wrong pump on the motor installed . In the early years I was swapping 340's quite often.
They didn't last me long I was very hard on them in the 70's street racing them . I saw this first hand. I always ran the smaller impeller pump. Now idling with AC or higher gears such as 323's need the larger dia. pump impeller with more fins was better if you were a light foot. I always wore steel tips if you get the hint. I didn't care about blowing motors. I had several more at home. which should be known by my thread pictures of my past.
Your choice of cooling is made by your HP + gear ratio + your driving. Vacuum leaks or timing effect heat more than you all would think. a good exhaust is also instrumental. To large or to short is not good for a motor. .
Most Hemi SS cars have a cone that drops their exhaust header from 4" to 2 1/2 " at the collector and back to 4" Big short exhausts make less power and more heat. If you are running a full exhaust with mufflers you can use large pipes. I ran 3 1/2 through mufflers with a restrict-or made by my tail pipes. I tried both ways open and full exhaust. The open made more heat and less torque I include picture of what I have tried.
The point is your cooling system isn't the only thing that will make it run hot. Trial and error is how I learned . at times it got quite expensive. As seen by my car I wasn't concerned about the looks more than performance. But it had to look all factory when walking around the car. The element of surprise. Hence the tips. LOL
Note there was no thermostat on the 340 fans here is a picture and the pic of the collector is from Bartons Hemi Dart
