If the coolant move through rad to quickly no cooling will be done.
To me there is a very simple way to approach this thought:
If you double the size of the radiator, will it cool a specific engine better/easier? If you run a pump that doubles the flow through the radiator, that is exactly what you have done.
There is much more to it than that, but with anything we have access to, there is no concern with moving coolant too fast in even a halfway modern automotive cooling system.
You REALLY want the thermostat to have to do its job all the time. If its having to work to keep the engine temp at it's set temperature, your cooling system has excess capacity. When the thermostat exceeds its rated temp (within production tolerarance) the cooling system is unable to cope with the load.
Edit: late edit, I really don't want to rehash this. But I like facts and science. Science paper here showing heat dissipation based on volume of liquid pushed through a radiator (PG5):
https://www.researchgate.net/publication/304364356_Radiator_Heat_Dissipation_Performance BLUF: more coolant flow equals more heat shedding.
Calculating heat absorption:
https://sciencing.com/calculate-heat-absorption-6641786.html Play around with the formula, you'll see two gallons of water (7.58kg BTW...Glycol will change the numbers, but not the physics) takes more energy to heat the colder it starts....in other words, the colder the coolant coming out of the radiator, the better it will absorb heat in the engine. The warmer the coolant is, the less heat it absorbs...so it takes longer to absorb less heat. Cold coolant absorbs more heat, faster, than hot coolant does.
"...as velocity of water increases heat transfer rate increases (Q)..."
Page 6
"...for a given heat load and coolant flow rate, the coolant temperature drop through the radiator will be constant, and nothing anyone can do to the design of the radiator can change that. Adding
rows or fins or face area or whatever will not change the temperature drop through the radiator. As a general rule, cooling systems are designed to operate with a coolant temperature of about 190 degrees F at the radiator inlet and have about a 10 degree F temperature drop through the radiator at rated power and rated coolant flow. This will result in a bottom tank temperature of 180 degrees F."
https://www.enginebasics.com/Engine Basics Root Folder/Engine Cooling Pg2.html
Under no circumstances is slowing the coolant down a good idea when it comes to cooling an engine down. (again, ignoring pump cavitation, fluid movement in the block, etc) The longer coolant stays in the block, the hotter it gets, and the LESS heat it absorbs. But as linked above (numerous times), if the coolant speed is changed, so is the amount of heat shed.
