So you seem to be quoting from discussions such as this https://www.eng-tips.com/viewthread.cfm?qid=262583
Not a single respondent to that stated that they were a -hands on- Chemical or Hx engineer and the info given reflects that. Top hit in google isn't necessarily correct.

Laminar flow can affect both the airflow and coolant.

There is a dwell time required for both the air and coolant to absorb or shed heat.

Despite what we observe in the top of a radiator, the coolant in an engine dose not achieve/maintain turbulent flow (exceeds its Reynalds rating) through the entirety of the system (if at all), there are many different flow rates occurring in the different sized passages.

This leaves laminar flow as the predominant effect, with much of the heat moving slowly on the edges and fast moving cold coolant channelling to the centre of flow.

Hence the balancing act of flow rates, volumes, materials in play, size of condensers and so on that every auto manufacturer has had to do for over a century now.

If it were as simple as "make the coolant flow faster", there would be only a few different smaller radiators in use and water pumps would be multistage jobbys flowing many multiples of the volume (and pressures?) in use now.

I use manually controlled heat exchangers on a regular basis and I can assure you if the coolant is too fast, performance can drop to the point of not working at all.

No, im not an engineer, just a tinkerer and a thinkerer

There is a HUGE issue with your thinking regarding how much time the coolant stays in the radiator. Thinking and saying the coolant has to stay longer in the radiator to absorb more heat is a circular logic. And a flawed one.

Any and by any I mean ANY restriction in the flow of coolant (or air) degrades the cooling systems ability to do its job. That’s a simple fact. Look in the Factory Service Manuals for different years of engines and you will see the performance engines had OVERdriven water pumps. Not UNDERdriven. UNDERdriven might work in a low performance application but where coolant temps are critical (this could be for any number of reasons but a couple would be making more horsepower requires more cooling and running higher compression on limited octane fuel such as pump gas requires engine temperature to be controlled and as such in my 11.77:1 pump gas engine I keep the coolant temp at 160 to control detonation) you overdrive the pump.

Under driving the pump was a 1990’s fad that should have died with the 90’s.

So while you are tinkering and thinkering, consider this. Every time you leave the coolant in the radiator longer, the coolant stays longer in the block. Where it picks up more temperature and that means you start taxing the cooling system harder.

An air to water cooler (thats what a radiator is) is limited in its ability to cool by whatever the ambient temperature is. That’s one reason a thermostat is needed, even though it’s a restriction. You have to set the MINIMUM coolant temperature with it so that on days where ambient temperatures are low you can get the required minimum temperature you need. For me, that’s 160 or the heater becomes less effective. And I’ve driven my junk in near zero weather.

Along those lines, let’s take a look at a 100 degree day and think it through. In this case, the lowest possible coolant temperature you can attain is 100 degrees. Of course, that doesn’t happen because you have a thermostat to regulate minimum temperatures AND because as the delta T decreases (thats the difference between ambient and coolant temperature) the ability of the coolant to drop the temperature becomes less effective.

In other words, let’s say you have a 190 degree thermostat and it’s 100 degrees ambient. You have a 90 degree difference. If we have an ambient temperature of say 60 degrees you’d have a 130 degree difference. That change in temperature differential between those two ambients means the lower ambient temperature has more cooling capability than the higher ambient. And those numbers are taking for granted the cooling system is good enough to maintain thermostat temperature on a 100 degree day. Most cooling systems aren’t well thought out enough to do that so you may be at 195 or even 200 degrees of engine temperature and that makes it even less efficient.

All this matters because the longer the coolant stays in the radiator the longer it stays in the block, picking up heat. If you have enough coolant flow that when the coolant temperature is at your thermostat rating, then it’s easier to keep the coolant at that temperature. But, if you don’t have enough coolant (and/or air) flow, the n forcing the coolant to stay in the block longer taxes the system harder.

You need the coolant speed to make the coolant take on as much heat as it can to reduce hot spots and to cause turbulence. Laminar flow (air there really is such a thing in a cooling system) might sound good on paper but it’s not.

When you see a cooling system that can’t maintain its thermostat rating you KNOW that the coolant is moving too slow thereby staying in the block too long, or you don’t have enough airflow or both.

It’s time to slay the wives tale that keeping coolant in the radiator longer is the correct way to do it. It’s not. It’s bad.

Do you even see the logical fallacy in your argument?

Actually Moroso was selling under drive crank pulleys at least 20 years before that. I think they were more interested in parasitic HP loss and high rpm pump cavitation than street car cooling. We used them mostly in drag cars.

What Mad science has said probably came from research at the University of Minnesota which has been leading in heat transfer study since 1887. They could be wrong, or the physics in some radiators is different than the rest of the universe. More/faster flow is good, slow is not. Some rumors are persistent through time, and this "too fast through the radiator" will come up again. But it won't be true then, either.

I have spent over 25 years in various engineering capacities several of which dealt with cooling.
The1st, 2nd, and 3rd bolded statements by 83 hurst IMO are correct. especially #3

The 1st statement by MS is not, an automotive radiator does not generate heat.
The 2nd Statement in is also misleading as the entire system design has to be considered many vehicles will overheat without a t/stat in place. Please see LINKY
The 3rd statement is true to a point, BUT if the radiator, fan and flow rates are correctly designed that heat will be dissipated
The 4th Statement if it moves too fast in the block or radiator it will not have enough time to absorb or shed the heat (See above link)
The 5th needs clarification on "maintain its thermostat rating you KNOW that the coolant is moving too slow thereby staying in the block too long, or you don’t have enough airflow or both." Too hot or too cold ?

The last statement "It’s time to slay the wives tale that keeping coolant in the radiator longer is the correct way to do it. It’s not. It’s bad." I also disagree with as once again, it goes back to the design of the entire system.
Not trying to start a p'ing contest just stating my experience's and opinion's

Go look at the formula for calculating thermal transfer efficiency. Guess which variable isn't in it? Time.

https://www.researchgate.net/publication/320490866_Performance_Analysis_of_Automobile_Radiator

So Sniper's link is about the construction of a cross flow radiator and its configurations. They are comparing radiator designs against each other, so everything is consistent. There is nothing considered concerning over heating. Yes, I read it.

TJP's linky is specifically referring to over heating, its primary concern is low air flow through the radiator. It appears to be an article in a news paper from a guy that had an over heating experience on an LA freeway, so it may well only be an opinion as well.
It does state "If for some reason the air flow rate through the radiator is too low, the radiator won't be able to do its job and the engine may overheat. At this point (after over heating) If the coolant flow rate is increased the engine will then transfer more heat to the coolant which will exacerbate the situation. I looked it up, exacerbate means to aggravate or irritate. Yes, I read it too.

The battle rages onward!

The battle rages on because of the myths perpetuated that will not die.

Think about it.

The longer the coolant stays in the radiator, it’s also staying in the block longer. Where it picks up more heat. That means the radiator has to dump more heat. So staying in the radiator is adding to the heat load the radiator has to eliminate.

We are working with limited temperature differentials. On a 100 degree day, the difference between that ambient temperature and your coolant temperature is less than it is if the ambient is say…60 degrees. That temperature differential is what makes cooling possible.

What your temperature gauge is telling you is the AVERAGE coolant temperature at the intake manifold. You can (and probably will) have localized coolant temperatures much higher than what the gauge says.

Getting the coolant out of the block quicker (more flow) will reduce local hot spot temperatures because the coolant is moving out of those areas so it’s not allowing the temperature to build up in those places.

You can always tell when a cooling system is inadequate. When the temperature on the gauge is higher than the rated temperature of the thermostat you’ve got issues. If you have a 180 thermostat then your gauge should stay between 180-185 in ANY weather conditions you may incur. On a very hot day, you may see an additional 10 degrees of temperature sitting at a LONG stop light or (alike happens to me if I’m not paying attention) if you get caught waiting for a long train to get out of the way. But as soon as you start moving the temperature should go back to where it normally runs.

If you have a 180 thermostat and your normal operating temperature is say…195 then your cooling system is inadequate. That then is a coolant and air flow issue. Too slow of coolant speed or not enough airflow or both.

The thermostat sets the MINIMUM operating temperature. That’s all it’s job is. It’s a restriction and that’s BAD, but it’s necessary. I have to run a thermostat. If I don’t, even on a 90 degree day my coolant temperature won’t go over 120 degrees or so. On a 50 degree day it won’t go over about 90 degrees. That’s because my cooling system is fully capable of controlling coolant temperature like it should so the thermostat does exactly what it should do, and that’s set the minimum temperature.

There is a reason why guys can go from a 190 to a 160 thermostat and the engine doesn’t stay any cooler. The cooling system is inadequate to deal with the heat load it has to deal with.

I run my water pump at 6% overdriven and if I could I’d double that or a bit more. We had some 108 degree days several years back and my engine temperature was at 160 even in that heat. At stop lights it would get to 175ish and then it would drop back down to 160 once I got moving again.

The backwards thinking that the coolant has to stay in the radiator longer to dump more heat is a fallacy, because the coolant stays in the block longer picking up more heat that the system has to deal with.

Mad Scientist, I don't think you can ever dispel this myth. There is some myths that will never go away. My favorite, besides this topic, is the Pennzoil myth. I'm not sure how to say this nicely, but both of us should maybe consider that the scientific principals of heat transfer apply evenly throughout the universe, with the exception of some radiators installed in mopar cars and trucks. Have a nice day guys......hang in there

Since you're interested in qualifications, I am an engineer that has done heat exchanger modeling, and have quite a bit of experience with air to water heat exchangers. You learn a lot when you learn to calculate things beyond just Reynolds Number... since you've been busy on google trying to find a place where I copied an argument from (and I didn't), I recommend you research Nusselt number and understand how it works.

Here's a simple explanation. Put your soup in the microwave to heat it. This represents a cross section of a tube in a heat exchanger. You run the microwave for 90 seconds, and you find that the edges are blazing hot and the center is cold. Why? The fluid is heating via conduction and not mixing (like laminar flow)... So what do you do? Stir it! Imagine if you could actually stir the liquid while microwaving - that would be efficient. Turbulent flow turns conductive heat transfer into convective heat transfer and greatly increases the heat transfer capacity of the system.

I may have missed it (this is a long thread) but no one has mentioned that the rate of heat transfer increases as the temperature differential between the hot object (engine in this case) and the cooling fluid increases. So that would support the postulation of not moving fluid slowly through the block if you want efficient heat removal. You wouldn’t run a small radiator fan(s) so that the air has more time to remove heat from the radiator because we all should know that would result in poor heat extraction and thus an overheated engine, so why would you reduce the flow of the water pump?

Not to go off-topic, but “Pennzoil myth”??? High paraffin base stock that leads to sludge/varnish under high heat???

Gee, that is a really nice write up.

Except, the thermostat temp (160, 180, 190) is the temp the thermostat starts to open, not the temp it is fully open. If you have a 180 thermostat and your coolant temp is 180, either your gauge is incorrect, or your thermostat is not operating correctly. Of course that also depends on the location of the gauge sender, in relation to the thermostat, and you are assuming the gauge sender is submerged in coolant and not in a trapped air pocket.

A cooling system that can maintain the coolant temperature within 10 degrees of the thermostat rating is functioning correctly.

I've been playing with cooling systems on cars & trucks for a very long time. There is very seldom (read that as almost never) one "fix" that works every time. Usually is a combination of "fixes" that have to be tested to determine which one(s) will cure the issue. Air flow that passes through the radiator traveling all the way through leaving the engine compartment, and obstructions and alterations that change coolant flow speed (fast or slow) from the original design are usually right after coolant leaks as the places to start. Outside of poor maintenance, modifications to the cooling system (or the motor) are usually the causes of cooling system failure.

Question if you take the radiator, water pump, thermostat, coolant or everything to do with liquid cooling out of the picture for engine cooling what would be the main component for cooling the engine?

Is this like that Schrodinger's cat question?

I think my answer is the state of the tune-up

Gus

Moparts: where you come to get lectured on the intimate Laws Of Thermodynamics, Boundary Layers, Air Flow; but you still haven't fixed your overheating dilemma.

Just trying to show how surface area, material, and air flow IMO have as much or more to do with engine cooling than flow rates and radiator cores. I've raced air cooled motorcycle engines for a long time and in the late '70's early '80's high performance motocross and off-road motorcycle engines became liquid cooled and we dealt with the overheating issues and mostly (but not exclusively) the problems were caused by lack or reduced air flow. On air cooled engines it relied on the surface area of the cylinder fins, the material (aluminum) and the air flow across and around the cylinder and cylinder head fins. When we went to liquid cooled engines all we were basically doing was using the coolant as a medium to take the primary source of heat engine combustion and taking it to one or two aluminum radiators and dissipating that heat to air. No real rocket science except in air flow with radiator side panels as scoops and our engineers even came with side panel or radiator "shrouds" that had opening that created a "chimney effect" that would help remove hot radiator air from behind the radiators at slow speeds or even at a standstill. Engines are still air cooled in my opinion they just use coolant to take that heat to a radiator or air cooling area. That's why I feel or know that air flow, surface area and material are most important. Check out this air cooled, 500cc single, hemi head, twin spark plug 60+ HP motocross bike from the early '80's. Lots of aluminum cooling fin area with lots of space for air flow. BTW most liquid cooled motocross bike still use the same basic size aluminum radiators to this day. Only a few things have changed like special radiator coating rather than black paint to better dissipate heat or small electric fans on the backside of the radiators for extreme slow moving conditions. AIR FLOW IMO is a key element.

CLARIFCATION The link is to an article, in a publication, by the California Institute of Technology also know as CalTech.

The article is in response to: Question of the Week: Why Does an Engine Cooling System Have a Thermostat, and How Does It Relate To the Coolant Flow Rate?

Submitted by Bill McLellan, Pasadena, California, and answered by Melany Hunt, Associate Professor of Mechanical Engineering, Caltech.

I'm going to go out on a limb here and say Ms. HUNT likely knows more than all of us on this subject

Yeah I get the airflow deal. All you have to do is look at the duct work on a cup car to see the science behind air flow to EVERY component on the car that generates heat.

Gus