Technical Coolant moving too fast through radiator to cool?

In virtually every "my engine runs too hot" thread there will be a suggestion that the coolant may be moving through the radiator too fast to cool it. Does anyone have facts to support this? If it's moving through the radiator too fast to cool, then wouldn't it also be moving through the engine too fast to pick up heat?

Discuss.

 

I can't weigh in with hard evidence, but moving too fast through the engine to pick up heat would also be a bad thing.

 

Ive heard that before but don't know how true it is. It makes sense in my head but in a practical sense it seems that you would have to have one hell of a hi flowing water pump. I have seen restrictors that go in the thermostat housing from Moroso before that take the place of a thermostat that are supposed to slow the flow down when not using a thermostat. Maybe there is truth to it.

 

I find it hard to believe. Just about everyone I have ever known that had cooling problems had tried to short-cut something : worn out parts, parts too small, parts mismatched, etc., etc., etc. Just about all got fixed when they stepped up and did it right. This applies to a lot of other areas as well.

 

I believe the water not staying in the radiator long enough to cool is BS.

 

A friend of mine and competition engine builder believes in this theory along with higher pressure inside the system to make sure the coolant stays in contact with the head/block surfaces. He has made and sells his designed water pumps and we use one. With that said our racing radiator manufacturer told us to remove the restrictors in our system because we went to a double pass radiator. He told us the restriction of the tubes was enough. The pump guy does not like double pass rads but we now run 190 while racing and 200 during yellow flag laps. Just some experience we've had..

 

I worked for Chrysler in 74 and 75. The parts dept said the A/C equipped V8 pump was different than non-AC and the AC pump slowed the coolant down.

You may not be able to confirm that difference at a replacement store listing. It would show up in a genuine old Mopar Parts book.

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100 % b. s.

 

Pull your thermostat out and get back with us. If the water doesn't stay in the engine long enough to pick up the heat, it over heats, same is true of the radiator giving up it's heat. They go hand in hand.

Hard facts on paper, don't have. Seen it happen, more then once......

Joe

 

Unless you have air or steam bubbles in the system, the coolant has no choice but to stay in contact.

 

http://www.pirate4x4.com/tech/billavista/Cooling/

A little research for you


Sent from my iPod touch using The H.A.M.B. mobile app

 

I've seen it on pickup trucks that the owner pulls the thermostat out thinking that it won't overheat. They tend to run hotter than if you just hull the thermostat out and use the shell of it as a restrictor.
I've never had an overheating problem when towing that way and ran the 350 that used to be in the 48 that way in the summer when temps were over 100 for days on end. It sure doesn't get much heat out of the heater the first morning that the temp drops down in the 30's though.

It still comes down to the simple fact that the whole heat transfer setup needs the proper time to transfer heat from the block to the coolant and then from the coolant to the air though the radiator.

 

Just FYI
http://stewartcomponents.com/index.php?route=information/information&information_id=11
I've seen a car run hot when someone removed the thermostat, and putting a washer back in there made it run cool again. At the time, I thought it was because it slowed the water flow down, but now I think it was because it caused pressure to build up in the block, increasing the temperature where the coolant would boil, as it flowed through the block. Steam is not a good conductor of heat. I've seen lots of arguments about this, but never seen real proof, one way or another.

 

I asked a friend who is a 50 year HVAC tech. He said it doesn't matter. If you take one water molecule and assume that it travels through the system once every 60 seconds. If you speed it up to once every 30 seconds, it will be in the engine, or the radiator, for half as long, but twice as many times. The net effect is it is still in contact with any given part of the system the same amount of time. I'm sure that if you take this to ridiculous extremes, overheating would be a problem.
Circulating the coolant once every hour might result in catastrophic failure

 

The thermostat causing a restriction, that builds pressure to prevent boiling in the heads, sounds like a good explanation to me.

Thommyknocker's link has some good info in it, about the myth of how heat transfer works. But most of the folks here don't really understand engineering math, what the term "exponential" means, etc.

Bottom line, if you can figure out a way to keep it cool, then go for it. I've found that a bigger radiator, and a big fan that is well shrouded, help a lot.

 

No empirical data, but I do have an observation from 20+ years of home brewing. I have an immersion cooler that goes into the hot wort at the end of the boil, its fed by cool tap water. If I run the water fast through the cooler it comes out mildly warm. If I slow the flow down the water exiting the cooler shows considerable heat to it. Now fast or slow which is ultimately best in beer making, or engine cooling I'll let others decide. I just know what I've seen.
-Dave

 

here ---> LONG and i mean long read but please take the time...
its worth it...
http://oljeep.com/rad/edge_radiator.html

 

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The exit temperature AND the exiting volume determine how many BTUs are leaving the system.
Just cause it's cooler does not mean fewer BTUs are being removed

If when eating an ice cream cone in the car, a window is open the ice cream melts FAST. Even a slight air current does a lot more heat removal>melting than still air.

Water is a pretty crummy conductor of heat. Wet suits work by holding water close to the body, and keeping it there. Swimming around naked the warmed up water gets swept away constantly, and the new, cool water pulls a lot more heat out of my old carcass.

 

I have personal experience in this area. My 1963 Fairlane has a later 302 in it. When I got the car the water pump was leaking sooooooo in my infinite wisdom I installed a kick ass High Flow water pump. From that point on it would never cool. Running 220 - 230 going down the road. Tried 4 different radiators. still no luck. Went back to a stock 3 core brass radiator and a stock water pump and it runs right at the thermostat, 180 degree.

 

i had a customers flat head that ran hot, we tried everything to get it to run cool. it was suggested to use two washers with 5/8 holes in the hoses and it ran cool. two years later the motor started smoking [unrelated?] and we took it out to rebuild. after the rebuild it didn't need the washers for some reason.

 

Q = M x C x Delta T......simply the higher the mass flow rate M, the greater the heat removed Q.
Flow rate is also important to achieve turbulent flow at all points in the system. Laminar flow
impedes mixing of hot and cooler fluids in a passage. Heat induced by pumping (pump heat)
can be considerable...in other words using a 50 gpm pump intended for promod would likely
be a detriment on a street car.

 

Actually anyone who says that the water doesn't stay in the radiator long enough to cool off is backward thinking. The purpose of the coolant is to cool the engine.

Heat is energy, when your water is in the radiator it is expelling energy, that is pretty easy. The purpose if the T stat in a street motor or a restrictor in a racing motor is not to keep the water in the radiator, it is to keep it in the engine. While it is in the engine it is absorbing energy, as much as possible, then it transfers to the radiator where the energy is expelled. The radiator or cooling coil is always more efficient at using energy than the engine is at creating it.

 

Myths
For those that cling tenaciously to myths, I am going to take one last crack at forever dispelling the Granddaddy of them all when it comes to cooling systems.

The myth is stated as either:

1. Coolant can be pumped too fast through the engine for it to absorb enough heat, or
2. Coolant can be pumped too fast through the radiator for it to cool properly, or
3. Cooling can be improved by slowing the flow of coolant through the radiator so it cools more completely.

NONE of these is true. The simple truth is that higher coolant flow will ALWAYS result in higher heat transfer and improved cooling system performance.

The reason the myth is so persistent, is that: a) without knowledge of fluid dynamics and laws of thermal conduction it does make a kind of intuitive sense and b) it is based on a tiny kernel of truth, but that kernel of truth does not explain the overall system behaviour and so, interpreted out of context, leads to a completely erroneous conclusion.

So, let's start with the tiny nugget of truth. If you had a sealed rad (no flow) full of hot coolant, and subjected that rad to airflow, yes, the longer you left the coolant in the rad, the more it would cool. However, if you were to plot that cooling over time, you would find that the RATE at which the cooling takes place is an exponential curve that decreases with the temperature difference between the hot coolant and the air. Put another way - when the temperature difference (delta-T) between the hot coolant and the airflow is large, heat transfer (cooling) initially takes place very, very quickly (almost instantaneously). But as that happens, and the coolant cools, the delta-T becomes less, and the RATE at which further cooling happens gets less and less until the point where the coolant and air are almost the same temperature and continued cooling takes a very long time. This is Newton's law of cooling. To illustrate this, recall my "quenching steel in a bucket" analogy.

A good example of this law can be seen when quenching a red-hot piece of steel in a bucket of water. At first, the temperature difference (delta-T) between the red-hot steel and the water is huge - therefore the initial heat transfer occurs at a great rate - the steel initially cools very fast - almost instantaneously. However, after this initial cooling, the delta-T is much smaller, so the remaining cooling occurs much more slowly. If you removed the steel after a second or two - it has cooled a lot - but it will still be warm. To continue cooling the steel to the temp. of the water, you have to leave it in there quite a bit longer - because as it cools - the rate of cooling continually decreases as well. In short - initial cooling is fast, but subsequent cooling occurs more and more slowly until cooling that last little bit takes a long time.

So what does this mean? Basically it means, the longer the coolant stays in the rad, the less efficient the cooling that takes place is - to the point that the rate of cooling is so slow as to be detrimental to overall system cooling. Better to dump the big load of heat right away and go back quickly for another load than hang about waiting for a last little bit of insignificant cooling to happen.

 

I had a 1932 Hupmobile with a straight 8 and an un pressurized cooling system with a new radiator. I had to put a restrictor in the upper rad hose to slow the water flow down, as the pump pumped more water then the core could flow and it would pump all the water out the over flow. Then it would over heat. But not the same thing with a modern pressureized cooling system.

 

From Water Pump Manufacturer Flow Kooler:
Doesn't coolant need more time in the radiator to cool?
No. But a lot of people still think so. We have come up with some explanations for the Doubting Thomas.
Debunking the I Can Have It Both Ways Theory

The water has to have "time to cool" argument is most common one we hear. In a closed loop system if you keep the fluid in the heat exchanger you are simultaneously keeping it in the block longer. Unfortunately, the block is the part that is generating the heat. Sending hot coolant from your source (engine) through the heat exchanger (radiator) to the sink (air) will transfer heat as long as there is a temperature difference between the source and sink. The engine is still generating heat the whole time so why keep the coolant there any longer than you have to.

Debunking The Conscientious Electron Theory

We hear that the coolant has to stay in the system longer to cool but what is heat transfer really but conduction, convection and radiation of electrons. The fluid in your system transfers those electrons based principally on the source-sink differential and the exchange material's transfer rate. An electron moves at varying speeds - Bohr's model has it moving at 2 million meter/second and with a mere 11 million eV boost you can get an electron to 99.9% of the speed of light. Though they move at varying speeds physicists accept that electrons move fast - really really fast. Far faster than the flow rate of the water pump. Your engine coolant's electrons do not know (or care) how fast you send them through the system - they just knows that the source is hotter than the sink and off they go.

Debunking Grandpa's Flathead Theory

"But wait a minute, I know Grandpa used to put washers in his flathead to slow the flow and cool his engine." We know people did this too. They still do it but the cooling benefit is not from the slower flow but the increase in dynamic pressure in the block that builds from the restriction. Consider that Grandpa had two flathead water pumps sending twice the volume through the same size radiator core as the Model B 4 cylinder. Too much flow in this no pressure system results in fluid loss. Slowing flow rate helps prevent that. At some point Grandpa maxed out the throughput and began building pressure in his block. Increasing block pressure helps reduce the onset of hot spots on his cylinder walls and formation of steam pockets in his block. This is a real benefit and does help cooling but is only realized when throughput nears capacity or is at capacity. While these restrictions may make sense when your rpm is excessive or your flow rate exceeds your heat exchanger throughput, they do not make sense for most applications. If you doubt this thinking then try this simple Ask Dr. Science experiment; clamp off the lower hose while you watch your temp gauge. Hopefully, you will debunk Grandpa's theory yourself before you experience vapor lock and melt your engine.

Flow restriction is not all bad if it serves to prevent cavitation. Cavitation occurs when a pump turns so fast that you generate lower pressure and air bubbles or vapor forms. These bubbles eventually implode and damage the engine block wall and impeller. Rapidly spinning the impeller can literally rip the air from water but may not actually move the fluid, it's tantamount to turning an eggbeater in a paint bucket. Restricting the fluid flow to raise system pressure in the block may help prevent cavitation at higher RPM but is it necessary for most vehicles? Probably not.

Most vehicles do not need to restrict flow because they do not reach or sustain high RPM. Additionally, thin aluminum radiators already restrict by design e.g. fewer rows of thinner tubes. Restrict it further and you may as well hose clamp the lower radiator hose and we know how that works out. When you face Grandpa on the track you may want your washers, otherwise, keep them in the toolkit.

Simply put, you have a far better chance of keeping your cool with greater flow rate through your heat exchanger and exiting the system than holding it in your heat exchanger while generating heat in your engine block.
2. Low Flow Luddites or..."the guy at the shop said"
When we are chasing an overheating problem, its common to seek help and who better than the guy sitting at the counter in a parts house or the countless experts begging to be heard on internet forums. They are generally excellent credentialed sources but we sometimes meet a low flow believer who thinks heat exchange is determined by how long the fluid stays in the block and how long it stays in the radiator. We fall back on simple logic. FlowKooler pumps achieve higher flow rates through a better impeller design. The high flow rates are seen far earlier on the rpm curve than OEM and self-professed "performance" pumps which use OEM-like impellers. The flow is more efficient builds block pressure sooner which helps in preventing cavitation. All good stuff which no one would refute. The low flow proponent' s argument of "too fast" begins to falls down when we discuss flow itself. If spun fast enough, even the most poorly designed stamped steel impellers will achieve the same hi flow flow rates. Granted they may cavitate, they may pump less efficiently and it will always occur at higher rpms. The point here is whether a discount design pump was spun at hi rpms or our well designed pump was spun under normal driving conditions; flow is flow. Can it be logically argued that a hi flow pump flowed coolant too fast if an OEM pump achieves the same flow rates. No, it cannot.

 

That all sounds good (an I use flow cooler pumps because they pump) but they bypass when the gate is closed just like any other pump. The thermostat is the gate so unless you don't have one (anyone reading this will agree that you need one) when it is not open the pump is not moving water through the block.

I may also add that an automobile cooling system is not a closed system, if it were there would be no need for a catch can. in a closed system (I have worked with them heating and cooling) you have to manually bleed the air.

Flow coolers are good pumps, like I mentioned earlier, they actually pump the water, and because they move more water than many stock pumps (many late model pumps move quite a bit of water) they transfer the heated water to the coil more rapidly. That is a good thing.

The writer of the article is convincing us that the pump is good which it is, but leaving out some very important information, while adding information that does not pertain to the real world situation.

 

It is a hybrid closed system really - It is closed until pressure overcomes the rating on the cap, at which time it becomes a partially open system. So in "normal" operation I think it can be considered a closed system.

 

FIRST HAND FACT ~ My experience with engine overheating was a result of the water moving too slow , I had a water pump pulley the exact same size as the crank pull,if I got in bumper to bumper traffic he temperature would rise rapidly.

After many band aide fixes a old timer suggested I run a smaller water pump pulley and since that time my car NEVER runs hot,even on the 8 mile long parking lot they call a highway in Pigeon Forge,Tennessee.

I'm not a rocket scientist but I do know that if you speed up the water you keep it moving through the radiator and that is optimum for dissipating the heat faster/

BTW,if you are running a fan like this your guaranteed to run hot. HRP

 

I agree with the cavitation theory. Hot water boils easy, some back pressure prevents boiling. Slowing down the pump will also delay cavitation. I have taken out water pumps that had the impeller eroded as if by cavitation. They were not pitted by rust, they were clean and rust free.

 

I'll agree with that.