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Radiator Selection (New Question)

4K views 34 replies 9 participants last post by  slik 
#1 ·
Is it true that high water flow rate means less cooling time in the radiator?

I am using a Milodon Alluminum Water pump with 30% more flow capacity and a high flow thermostat they recomend to use with it.

With a high flow thermostat and pump, this means the water has less time to cool in the radiator before being re-circulated...right??

You guys with the derale electric fan and alluminum radiator using a high flow pump too? Is this also part of my issue?

I do have that new alluminum radiator on order, but while I have my water system drained, I am thinking maybe I should go back to a stock flow water pump... Or maybe just go back to a standard flow thermostat?? What about that forced thermostat closure issue they say happens from a high flow pump. ( Or is it forced to stay open...?)

This sound right to anyone out there?
 
#2 ·
Yes that is true.

I am unsure that a high flow pump will force a thermo to stay closed though... most thermo's are holding back temp adn a tiny bit of pressure but when the spring get's hot it will retract and it is very unlikely that the fluid flow will push it closed.

The temperature activated spring has a TON of closed pressure. Ever try opening one with your fingers? That same spring value is only slightly less strong when the spring is hot and open and it would take a lot of force to push it closed, much much more than any high flow water pump can push.


FE
 
#3 ·
FE, was it you who suggested the Book by Heisler? I went and bought one...

In his book, he describes how a thermostat works. Now I understand it. The cavity is filled with wax (inside) As the wax heats up, it expands and pushes a plunger away from the housing, along with the valve cap and creates an opening. You can not open it by hand, cause the wax has not softened and the plunger is frozzen inside of the wax.

When it is soft, it moves more easily.

But what is your opinion on the high flow pump, should I ditch it, or should my new alluminum radiator work fine with it?
 
#4 ·
On 2007-06-05 06:31, Mikes66 wrote:
Is it true that high water flow rate means less cooling time in the radiator?
Yes, but it also has less time to heat up in the engine. It's probably a trade off.

Now, if I had to speculate....

An engine with a huge radiator, one that could cool the water way down, even if it was pumped fast, would probably benefit more from a hi-flow water pump. Since the water spends less time in the engine, the water, and the engine maintain a more constant temperature... without the later parts of the flowpath getting hot.

But, the two factors probably cancel each other out for the most part. With a high flow pump, the water has less time to cool in the radiator, but it also has less time to heat up in the engine. Your new, larger capacity radiator will give the water more time to cool down.

I'd say you'll be just fine with the current pump. If it STILL gets hot, which I doubt, you can try changing water pumps.

My engine is half filled with Hardblok, has a Griffin rad of stock dimensions but two 1-1/4" cores, a Derale fan, and a simple belt drive electric water pump (Ford blower motor) with an overdrive pulley. I've removed the thermostat for higher flow, and just wait until the temp gauge starts to move before turning on the pump. It works ok. I'd like a little faster pump, but so far, so good.

You should be fine.

Good Luck!
 
#6 ·
The thermostat is simply a temperature regulator. Once the engine gets hot, and the thermostat has opened, it has done it's job.

Now, if the cooling system is working below capacity, the thermostat will open and close as the water temperature goes up and down to keep the engine at the thermostat's rated temperature... but it does not regulate the velocity of the water flowing through the system.
 
#7 ·
I also have a high flow thermostat, which flows 40% more then a stock thermostat. It's opening diameter is almost 7/8 the size of the thermostat where a stock one is only about 5/8 the size of the outside diameter.

There is a situation of having too good of cooling too. I will not have this issue, but some folks may.

If the water cools too much, your pulling colder water into the engine, and that will force a big temperature gradient across the cycinder walls, till it heats up again. We are not talking 30 - 40 degrees, we are talking 10 - 15 degrees. This can really harm an engine, by having a constantly changing temperature gradient, and rings just don't like that. The cold water goes to the lower part of the block first.

The most damage done in cylinder walls is when the engine is cold, before getting to operating temperature.
 
#8 ·
Many guys who race circle track use a restrictor in the water outlet instead of a thermostat. They use different sized restrictors to get the cooling they want.

These serve a few purposes... First, it's adjustable. Second, there is no thermostat to fail. Third, a restriction in the outlet also helps the pump to build pressure in the engine's cooling passages. This can help push the water into more nooks and crannies, and also squeezes out more air in the dead spots of those passages.

I could use a stronger pump and a restrictor in my engine. Right now, the pump isn't that strong, so I removed the thermostat for max flow. No thermostat also allows me to cool it all the way down at the dragstrip between passes. Turning the fan and water pump brings the temp down to 100 degrees or less PRONTO when the engine isn't running. A stronger pump and restrictor would probably provide for more even cooling and fewer hot spots when running in my car.

Mike, the high volume pump and standard theromstat might be the best combination for cooling your engine.

Good Luck!
 
#9 ·
You guys apparently didn't pay much attention in chemistry class...


Water Cooling Flow Rate and Heat Transfer

Q = M x C x Delta T

"In other words, the rate of heat transfer is directly proportional to mass flow rate. If you increase the flow rate, you will then increase the rate of heat transfer."

This is not a theory, this is fact. And yes, that's a computer website, but the math applies the same.

This does however mean that the most important factor in ensuring the efficency of cooling is placed squarely on the quality of the radiator itself (Delta T in the equation). Moving from the old copper style radiator to the newer aluminum, being about half as good a conductor as copper, is doing a small disservice to the cooling properties of the engine. You cannot do better than water as a method of heat transferrence since it has one of the highest specific heats.

Aluminum does, however, have the benefit of not corroding over time and blowing up unlike the old copper cores (galvanic corrosion can be a nasty thing).

So in other words, the better the radiator (inlet temp and outlet temp difference greater), and the more air you move over the radiator (higher cfm fan), the better the engine will cool. Your thermostat will not get stuck closed because of the flow, I can promise you that.

-J

_________________
http://www.concentricsoft.com/Personal/Jim/Truck/

<font size=-1>[ This Message was edited by: jrosengarth on 6/5/07 11:40pm ]</font>
 
#10 ·
On 2007-06-05 08:35, jrosengarth wrote:
You guys apparently didn't pay much attention in chemistry class...


Water Cooling Flow Rate and Heat Transfer

Q = M x C x Delta T

"In other words, the rate of heat transfer is directly proportional to mass flow rate. If you increase the flow rate, you will then increase the rate of heat transfer."
WHOA!!! This formula doesn't even mention flow rates!

TIME is a major factor. The longer the water stays in the engine, the more heat it will gain. The longer it stays in the radiator, the more it will lose. Simply pumping water faster through this closed system doesn't do what you are saying. According to your statements, pumping the water through the system twice as fast removes twice as much heat. That is terribly wrong.

This does however mean that the most important factor in ensuring the efficency of cooling is placed squarely on the quality of the radiator itself (Delta T in the equation). Moving from the old copper style radiator to the newer aluminum,
Copper is indeed a better conductor of heat than aluminum. But, aluminum is structurally stronger, so it can be made both thinner and the tubes can be made longer for better efficiency. Aluminum radiators can also be assembled with more efficient joints. (not, sloppy lead solder) Theres a LOT more to it than copper simply being a better conductor of heat.

So in other words, the better the radiator (inlet temp and outlet temp difference greater), and the more air you move over the radiator (higher cfm fan), the better the engine will cool.
The larger the capacity of the radiator, the more time it takes for the water to flow through it, and the more time there is for the water to cool. Where is TIME in your formulas?

Of course, additional airflow will make the radiator work better.

The puzzle at hand is far more complex than the simple formulas you provide as "complete" explainations. You seem like a bright kid, but once you get out of the -theoretical- the true engineering gets much more complicated. There's always a lot more going on that some would like to believe. Generally, a -little- knowledge can be a dangerous thing. Please, share what you know to be true, but don't take untested theories and tout them as fact. The formula you gave....

Heat = mass x specific heat x change in temperature
(Q = M x C x delta T)

along with the differences in specific heats of aluminum and copper come a LONG way from describing what goes on in an automotove cooling system.


_________________
66 mustang
302 4-speed 289 heads, 10.63 @ 129.3
http://www.mustangworks.com/cgi-bin/moi-display.cgi?220


<font size=-1>[ This Message was edited by: n2omike on 6/6/07 12:28am ]</font>
 
#11 ·
n2omike- Are you serious? Did you read the equation and the explanation? M is the flow rate in mass of water in the equation! All of that to say you want to disprove an known scientific fact?? Have you tested YOUR theory?

If you want a test of specific heat related to density, then I suggest you try this one: take two ice cubes, same size and shape. Place one in a cup of still hot water, place the other in a cup of running cold water. Which one do you think will melt faster? Works the same if the temperatures were inverted. In practice, this works. If you can get that equation to prove a lower flow rate cools better, then please let me know. We'll have to inform every school science department and lab in America.

By the way, if leaving cooling water in a heat exchanger (which is what a radiator is) for a longer period of time cools faster, then that's what power plants would do, but they don't. Oh, and I'm not a kid.
-J

_________________
http://www.concentricsoft.com/Personal/Jim/Truck/

<font size=-1>[ This Message was edited by: jrosengarth on 6/6/07 1:47am ]</font>
 
#12 ·
And almost forgot, I am not saying that cooling rate would double (first of all I'm not saying this, this is not my supposition, or a theory, it is a scientific fact). You would eventually reach a point where moving the cooling fluid throught the heat exchanger would no longer improve cooling capacity. That's just a fact of life, like critical mass or terminal velocity. Nothing is perfect.

Also, water's specific heat changes (gets worse) as it gets closer to boiling point, so by leaving the water in the engine block longer, thereby increasing it's temperature as you suggest, it's ability to cool becomes less. Again, just the facts, not like I'm theorizing on this stuff.
-J
 
#14 ·
jrosengarth...you are the man!! Everyone else needs to brush up on the 2nd law of thermodynamics....plus a few others. The higher the delta T (temperature differential) the faster and more efficient the transfer of heat will be. That's why you put your hot beer in the freezer for awhile instead of the refrigerator. It will cool down faster.
 
#15 ·
Your all right, there is a velocity of water that works fine, but going over that velocity does not do much more to improve the cooling in a closed loop system, without increasing pressure. Pressure is limited to 16 pounds, or the rating of the cap. After that, you start to impead the design of the impeller, and stall cooling flow rates.

Pressure is limited (probably can be folded into the density), and efficency of the construction of the radiator is another.

But, Mike is also correct, formulas do not capture every aspect of this motor stuff. Not being a kid either and working in a building full of scientist, I have heard the same arguements posed on a host of different subjects, and when posed in the real world, they don't always hold up. especially for racing. Experiance is the best tool, and that is what this site has to offer.

Trail and error is another tool, but I have a limited budget, and I already own a host of extra engine goodies that don't work as science would claim they work. Anyone want to buy a slightly used ( 1000 miles) brand new copper 3 core? Probably works good for a 6 banger....

Take for example... We all know a black body is the best emittor/absorber of infra-red, or heat... yet these alluminum radiators are not painted black. Why... because the amount of gain from the emisitivity of a black body is not worth the amount of cost to actually paint the radiator that color, and it increases the thickness of the fins, thus decreasing the inherent transfer properties to moving air across it.

It takes a little from Column "A" and a little from Column "B" to make these things go fast....

I have worked in advance science for 25 years, and last year I thought I had this issue nailed down by applying theory, but here I am again this year with the same issues. Now asking for help from folks that have gone through the same pains I am now, and I have my ears wide open, and my mouth shut.





<font size=-1>[ This Message was edited by: Mikes66 on 6/6/07 2:39am ]</font>
 
#16 ·
On 2007-06-05 11:16, carsnguitars wrote:
jrosengarth...you are the man!! Everyone else needs to brush up on the 2nd law of thermodynamics....plus a few others. The higher the delta T (temperature differential) the faster and more efficient the transfer of heat will be. That's why you put your hot beer in the freezer for awhile instead of the refrigerator. It will cool down faster.
Keep in mind... The faster the water is pumped through the radiator, the less it is cooled, so there won't be as much of a delta T as if it was being pumped through the radiator more slowly.

Anybody knows that the larger the temperature differential, the faster the heat is transferred. If icewater is put into the engine from the radiator, the heat from the engine will transfer more quickly than it would into warmer water. The slower the water is pumped, the cooler it gets as it passes through the radiator, and the larger the delta T is.
 
#17 ·
...We all know a black body is the best emittor/absorber of infra-red, or heat... yet these alluminum radiators are not painted black. Why... because the amount of gain from the emisitivity of a black body is not worth the amount of cost to actually paint the radiator that color, and it increases the thickness of the fins, thus decreasing the inherent transfer properties to moving air across it.
Paint is an insulator and changes the conductive property of the aluminum, that's why that doesn't work. Regardless, yes some things may seem to defy common sense especially in the automotive industry. A better example may be why using no exhaust headers (least restrictive) does not produce as much power as a well tuned exhaust system? We all understand, and I understand the reasoning behind aluminum radiators (I run them, and wouldn't run anything else, I'm glad they got rid of copper/brass), but the whole cooling thing is pretty simple. More coolant being flowing through the hot engine block, and being cooled better by a good radiator/fan = good.

You bring up a good point and that is at a point more flow would increase the system pressure, which is not so good. There is a happy middleground for everything. And sorry to everyone for the long rant, I get a little chaffed when someone claims that a well known law of nature is not correct.

-J
 
#18 ·
On 2007-06-05 11:32, n2omike wrote:

Keep in mind... The faster the water is pumped through the radiator, the less it is cooled, so there won't be as much of a delta T as if it was being pumped through the radiator more slowly.

Anybody knows that the larger the temperature differential, the faster the heat is transferred. If icewater is put into the engine from the radiator, the heat from the engine will transfer more quickly than it would into warmer water. The slower the water is pumped, the cooler it gets as it passes through the radiator, and the larger the delta T is.
(breeeath...ahhhhh). Ok, we seem to be misunderstanding the fundamentals here. The point is to NOT have a large Delta-T, the point is to saturate the heat exchange system with enough coolant that the temperature of the system comes into an equalibrium, and therefore REDUCE the Delta T to a minimum! In an engine system running 35 GPM (for example) if the water coming into the heat exchanger (radiator) is at 205F and the water coming out is at 185F, then the engine is running at 205F. In an engine running a 55GPM water pump if the water coming into the radiator is at 195F and the water flowing out of it is 190F, and the engine is running at 195F. You can only maintain this close equalibrium if your flow rate is higher, given both systems have the same volume of coolant.

-J
_________________
http://www.concentricsoft.com/Personal/Jim/Truck/

<font size=-1>[ This Message was edited by: jrosengarth on 6/6/07 2:57am ]</font>
 
#19 ·
Q = M x C x delta T

(Heat = Mass x Specific Heat x change in Temp)

This formula has NOTHING to do with rates. It is simply a way of calculating how much heat energy is required to raise or lower the temperature of a given mass of something.

For example, the specific heat of aluminum is 0.89 Joules/gram degree celcius. This means it takes 0.89 Joules of heat to raise each gram of aluminum one degree celcius.

This equation could be used to measure how much energy it takes to raise 120 grams 30 degrees celcius... (120)(0.89)(30) = 3204 Joules but, it has nothing to do with RATE of heat transfer. It is simply used to calculate the amount of heat that is transferred in raising the temperature of something.

This formula comes up way short when it comes to pumping the water through the engine and radiator more quickly. Your ASSUMPTION assumes the water in the engine reaches the full engine temperature as it flows through the engine, and it reaches ambient as it flows through the radiator. This is not the case. After shutting the engine off, the temperature gauge will rise. Plus, the water flowing out of the radiator is far warmer than ambient.

Your blanket statment of Q = m x c x delta t would only -maybe- hold true if there was FULL heat transfer as referred to above. In reality, that is NOT the case.

Water flows in big heat exchangers, as alluded to in carsandguitars post are closely calculated and experimentally determined to find what is most efficient. They don't just "crank em up" to max and let it go.
 
#21 ·
On 2007-06-05 08:03, n2omike wrote:
The thermostat is simply a temperature regulator. Once the engine gets hot, and the thermostat has opened, it has done it's job.

Now, if the cooling system is working below capacity, the thermostat will open and close as the water temperature goes up and down to keep the engine at the thermostat's rated temperature... but it does not regulate the velocity of the water flowing through the system.
Because of the water bypass in the water neck this is true. That keeps this from happening. Otherwise the venturi effect would cause the water to flow from one side of the thermostat valve to the other faster or slower depending on how open it was. This would also increase the pressure in the system (thus the bypass).
-J
 
#22 ·
On 2007-06-05 11:49, n2omike wrote:
Q = M x C x delta T

(Heat = Mass x Specific Heat x change in Temp)

This formula has NOTHING to do with rates. It is simply a way of calculating how much heat energy is required to raise or lower the temperature of a given mass of something.

...

This formula comes up way short when it comes to pumping the water through the engine and radiator more quickly. Your ASSUMPTION assumes the water in the engine reaches the full engine temperature as it flows through the engine, and it reaches ambient as it flows through the radiator. This is not the case. After shutting the engine off, the temperature gauge will rise. Plus, the water flowing out of the radiator is far warmer than ambient.
I give up. Mike, I urge you to pick up a book on the laws of thermodynamics. They are second only to the laws of physics in science. This is the second law. You are literally arguing a scientific precept that has been around for centuries. There is no theory involved. This is as fundamental as one of the laws of motion. I am sorry that this escapes you.
-J
 
#23 ·
It doesn't escape me at all. You are simply painting this picture with a very wide brush. You are overlooking all the details.

You are saying that pumping water through the radiator twice as fast will cool the engine twice as much. This is a totally FALSE statement. There IS a limit! I guess, using your example.... I could just install a radiator out of a Geo Metro in the mustang, and it would cool just fine as long as I pumped water through it fast enough......

THAT WON'T WORK!!!!!!!

You might want to study up on those laws yourself. Might even mix in a little actual experience as well.
 
#24 ·
Mannnn, this is wayyyyyy too textbooky. You guys have me lost. I will keep reading though... Not sure if you noticed, but not very many people have chimed in here. Wonder why. I failed physics in school. Was too boring for me. Seems like no one wants to agree to disagree. I am totally lost!! Thanks!
 
#25 ·
its geek talk --
daughter married one of them fellers -- takes him all day to make the toast --

opps sorry guys i forgot the smily face -- didnt mean any harm


<font size=-1>[ This Message was edited by: deadhorse on 6/6/07 5:04am ]</font>
 
#26 ·
On 2007-06-05 12:39, n2omike wrote:
It doesn't escape me at all. You are simply painting this picture with a very wide brush. You are overlooking all the details.

You are saying that pumping water through the radiator twice as fast will cool the engine twice as much. This is a totally FALSE statement. There IS a limit! I guess, using your example.... I could just install a radiator out of a Geo Metro in the mustang, and it would cool just fine as long as I pumped water through it fast enough......

THAT WON'T WORK!!!!!!!
It will if you move enough air (faster), that's cold enough (greater delta T) across it.
 
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