MustangSteve wrote:
I like to break things down to their simplest parts when a question comes up. I want your help to help me understand this correclty. It seems that someone posted an argument that keeping water in the radiator longer does not help it cool any more.
To simplify this, lets assume we have a simple radiator ALONE. No engine to complicate things. If I pour the radiator 100% full of 200 degree water and push it through the air for 30 seconds, the water will be cooled down a certain amount. Now, if I do the same experiment, but I push the radiator through the air for one minute, it would make sense to me the water would get colder than if it was only done for 30 seconds. I cannot see why this would not be true.
That said, the longer the water stays in the radiator, the cooler it will be when it comes OUT of the radiator.
Now, the complicating factor to this seemingly simple experiment is that the water being held in the engine by the thermostat is getting hotter and hotter all the while. Waiting on the water in the radiator to get as cool as possible is creating an adverse condition in the block.
So, there needs to be a balancing act involved. The thermostat holds hot water back until it reaches a preset temperature, then releases a bit of water into the radiator, at the same time, some of that cool water is coming out of the radiator. When the cool water reaches the thermostat, it closes down, maybe just a little, maybe alot, depending on how cool the water is. Then the cycle repeats.
The science of all this is sizing the radiator correctly to match the thermostat and the engine's mass and coolant volume so it all actually works. That is the class I slept through, I guess.
So...somebody 'splain it to me how water held in a radiator longer does not get cooled more than water held for a shorter time... I'm listening...
If your sentence, highlighted in blue above, is in reference to the information I posted, that is not completely what was said. Holding water longer in the radiator will cool it more --eeeventually. But, in the time it would take to extract a significant and useful amount of heat from the coolant, the engine is still banging away and continually inducing large amounts of heat into the water that's being bogged down inside it. The 'extra' time the water is held in the heat exchanger [radiator] isn't worth the (relatively) small amount of BTUs it would remove in relation to what's happening to the backed up water inside the engine.
If someone is experiencing cooling problems to begin with, slowing the flow through the radiator is only going to make the water being heated inside the engine that much hotter if the water inside the engine (the source of where the heated water is coming from to begin with) is bottle-necked by retarding the flow through the radiator.
The greater the temperature difference between two substances (Delta-T), the faster the (intial) rate of thermal transfer, but only up to a point. The article I posted illustrated this example by taking a piece of red-hot steel and quenching it into a bucket of ambient water for just a few seconds. Almost instantly, the temperature of the red-hot steel is dropped dramatically. You could take the steel out of the water and touch it but it would still be warm to very warm to the touch. You could put it back in the bucket to soak longer to cool it completely down to the temperature of the ambient water but, as the two differences in temperature (heated steel vs. ambient water) begins to get closer, the differences in the Delta-T become exponentially less and less --in other words the closer the temperature of the water and heated steel begin to seek equalibrium, it takes longer and longer for each degree of change to occur before they would finally become equal [it would take a long time for the total cooling of the hot steel to finally happen].
In the case of an internal combustion engine, if you're already having overheating problems, you don't have a long time to wait on slowed coolant flow through the radiator before you need to move the water out of the engine, that's much hotter and getting hotter all the while. It's better to move the water on through the radiator, through the engine and back to the radiator for another try at pulling a chunk of heat out of the engine coolant, than to let the water linger around in the heat exchanger, waiting for the radiator to pull an insignificant amount of heat difference from the coolant, before letting the hotter coolant in the engine move on.
If you have the correct sized radiator for the engine being used (and how it will be used), a good flowing water pump, abundant air flow through the radiator, then the thermostat should do its job of regulating the engine temp so that the engine doesn't run too cool in the winter or too hot in the summer.
Excerpt from another article on the subject of the lingering water theory:
Cooling FAQ
1. Doesn't coolant have to have 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 and electron to 99.9% of the speed of light. Though they move at varying speeds physicists accept that electrons move 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. At some point Grandpa maxed out the throughput and began building pressure. Building pressure in his block helped 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.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.
Full article at this link:
http://www.flowkoolerwaterpumps.com/cooling_faq.html
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