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Engine Specific Info and Questions => IDI Engine => Topic started by: Master ACiD on December 03, 2005, 07:48:55 am
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i have never seen a car with a bypass hose which goes from the waterpump right to the upper coolany neck. at first glance this seems counter productive to cooling?
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The thermostat is double acting, it closes the bypass hose as it opens to the radiator. When the thermostat is fully open the bypass is completely shut and all the coolant flows through the rad.
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IMO the only goofy aspect of it is the oil heater (cooler?). Flow through it on the golf/jetta is into the bypass hose which is blocked when the engine is hot.
Not really. The oil cooler has two coolant inputs. One goes to the bypass hose (which connects at the top to the main coolant input to the engine). The second connects to the return line from the heater. The return line from the heater also connects to the base of the water pump, which connects to the bottom of the radiator. This design allows the thermostat to regulate the flow of coolant to the oil cooler when the engine is cold or warm (ie, change where it comes from). When the engine is warm, cooled coolant flows out of the heater core return hose, into the oil cooler, and then into the bypass hose, which is connected at the top to the hot coolant return line to the radiator. When the engine is cold, the flow is reversed. Warm coolant flows into the oil cooler through the connection to the bypass hose, and then out into the heater core return line and down to the water pump, which then recirculates it back up through the bypass line. This has the effect of warming the oil when the engine is cold, and cooling it when the engine is warm. Those wacky germans eh? I love their designs. Anyway just thought I'd point that out.
Chris
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The problem with the way you described it is you would be expecting the hot coolant to do something it never does by itself, ie flow downwards. The cooling system is a thermal syphon assisted by the water pump which sucks from the bottom of the rad. The coolant that goes out the bottom of the rad and into the pump is therefore cold coolant that has sank to the bottom of the rad after being cooled by the air passing through it. Hot coolant will never, by itself, flow downwards. I think what happens is that some of the coolant that flows back from the heater core is sucked up through the oil cooler and into the main hot coolant return line that follows the thermal syphon into the rad and then downwards as it cools towards the water pump which assists the flow. To have hot coolant flow down the blocked bypass and into the oil cooler would mean that the hot coolant is flowing downwards (which it never does) and against the prevailing flow of hot coolant, which is upwards, into the main return line, into the rad, and then down into the water pump as it cools. The prevailing hot coolant flow direction, when the thermostat is open, is up, through the engine as it warms up, catching heat as it rises to the top in the cylinder head, out the main return line, and into the top of the rad (and it would smoke away as steam if there was a hole anywhere, because that is where it wants to go, straight up). There would never be a tendency for the hot coolant to flow downwards as it heats up. The only reason the hot coolant flows downwards is because it is cooled rapidly when it enters the rad, and the cooled coolant is pushed down (and sinks all by itself also) by fresh hot coolant continuously entering the rad from the engine. That is why the design of the oil cooler is so ingenious. Whoever thought of it saw the big picture and realized that hot coolant would never flow downwards and any cool coolant that reached the oil cooler would necessarily, as it went through the oil cooler and became hot, rise upwards towards the main return line to the radiator.
Now when the thermostat is closed you have the same effect. The only difference is the hot coolant coming out of the top of the cylinder head is forced back down through the bypass into the bottom of the engine (If the thermostat ever failed to open, what eventually would happen would be that the top hose to the rad would burst, and the coolant would all flow out that hose, mainly as steam, which would rise straight up, like it always does. None of it would flow downwards. The oil cooler would probably be quite cold, while the hot coolant gushed out of the burst top hose). But as hot coolant, it again doesn't want to go down, it wants to rise. So it takes the path of least resistance, through the oil cooler, and then is again forced down into the water pump which recirculates it through the engine. The whole system is designed around the assumption that hot coolant will not go down willingly. It always wants to rise.
Chris
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well heres what im thinking guys. i live in south florida. it gets to be 40 degrees celcius here in the summer, and we dont have a winter.
im thinking of disabling the heater core, because it leaks and i dont need a heater anyways. then im thinking of removing the heater hoses and blocking off the ports just to clean up the engine bay a little bit.
then in order to keep the overflow tank functioning i would just hook it up to the flywheel side of the cylinder head.
do you guys see any problem with this or does this sound like a bad idea? im open to suggestions.
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im thinking of disabling the heater core, because it leaks and i dont need a heater anyways. then im thinking of removing the heater hoses and blocking off the ports just to clean up the engine bay a little bit.
then in order to keep the overflow tank functioning i would just hook it up to the flywheel side of the cylinder head.
do you guys see any problem with this or does this sound like a bad idea? im open to suggestions.
Don't do it, at least not the way you described. If you wan't to defeat the heater core just connect the hoses together or place a short rubber elbow from the coolant neck on the flywheel end to the metal pipe that runs to the water pump. You can cut one of the heater hoses to suit. You don't want to dead end the coolant fitting on the head, the number 4 cylinder will get very little flow if you do.
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They have a valve in the line from the flywheel end of the head to the heater core. When that valve is shut all coolant flow on that circuit is stopped.
Wasn't aware of that, I've never eyeballed a north/south diesel in person. I guess it can be plated off then. It was my understanding that the coolant entered low on the front and exited high on the rear of the engine. I would have thought the flow would get a little stagnent around #4 (like it does in a 2.2 dodge...) with the heater hose blocked. But if the factory does it, it should be OK.
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Now I'll say you're completely wrong. The force of thermopsiphon has almost no effect on the VW cooling system. Actually the force is so weak compared to the waterpump that you could effectively say it has *absolutely no effect* and you would be right except perhaps in the case of the radiator where it *might* reduce turbulance *slightly*. The vanagon radiator actually draws cool from the *top* and inputs the hot at the *bottom*. The force of thermosiphon is so weak that it has *no aprreciable effect* on the flow through the oil cooler. In fact if thermosiphon were the force of movement through the oil cooler, the cooler would be utterly and completely useless due to the very small surface area and the temperature differential required to move coolant against the pressure differential of the waterpump. I used to imagine that the flow followed thermosiphon as you say until I was educated about it. Nope, you're totally and completely wrong about the coolant flow path.
Andrew
I don't think I'm wrong. The vanagon engine sits on it's side doesn't it? I've never seen one so I'm just guessing. But you know that hot coolant rises and cool coolant sinks right? And the cooling system is partially pressurized so some of the coolant that is right at the top, if it was allowed to escape, would do so as steam? Think about it. Steam rises, it doesn't sink. Hot water sits on top of cold water. There would never be a situation where hot coolant, that is beyond it's boiling point but not yet steam because it is under pressure, would flow downwards and displace colder coolant. It's just physics.
The water pump is definately necessary to move the cold coolant back into the engine, but the hot stuff is going to rise all by itself. Don't need the pump for that.
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Not sure on that MasterACid.
A couple more thoughts on the thermosiphon effect.
If it were a dominant factor in the flow path, then there would not be any flow to the waterpump prior to the thermostat opening, and so the thermostat would never open as it would never get any hot coolant to it, etc...
not really. As you probably know (if you've ever installed a thermostat) the element is on the inside. So it takes its temperature from the coolant that is coming back down the bypass line, not from the coolant that is in the radiator.
With regard to the force of thermosiphon as opposed to the force of the waterpump, imagine a 220v hot water heater element in a still water tank. How many ripples form on the surface even when the element in near the surface? Now imagine a waterpump, how many ripples are formed when it is near the surface of the water?
The hot water at the bottom of the water tank would rise to the top as the 220 volt heater heated it. It's just physics.
As I mentioned before, in order to push the water up to the high pressure hose the coolant would need to be well past the boiling point in the oil cooler circuit and thus would be utterly useless as a cooler.
Andrew
not really. The coolant is cool when it comes into the oil cooler. It then takes heat from the oil, making it warm, then it rises.
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well heres what im thinking guys. i live in south florida. it gets to be 40 degrees celcius here in the summer, and we dont have a winter.
im thinking of disabling the heater core, because it leaks and i dont need a heater anyways. then im thinking of removing the heater hoses and blocking off the ports just to clean up the engine bay a little bit.
then in order to keep the overflow tank functioning i would just hook it up to the flywheel side of the cylinder head.
do you guys see any problem with this or does this sound like a bad idea? im open to suggestions.
sounds like a plan. only thing i will add is that some early mkIs has non-overflow radiators... meaning they had a filler right on the radiator and no need for an expansion tank. if you want to clean up under the hood you could try eliminating the overflow altogether and see if you have any cooling problems. i have not done this personally (yet), but i have spoken with people who have, and despite their worry that the car would run hotter, in practice, it runs at approx the same temps.
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The carburated VWs are the ones that came with overflow tankless radiators.
I run a carburated VW Radiator on my 1.6lTD for weight savings and to clean up the engine bay... no cooling system problems. But - without the clear plastic overflow tank, you can't as easily check the coolant level. What I usually do to do a quick fluid level check is give the upper radiator hose a squeeze. Can usually tell that way if there is coolant inside it and if the pressure is right.
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I've got a 1984 Jetta with 1.7 cis throttle body, it came stock without the overflow bottle style.
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As far as I know all mk1 sciroccos came with the built in over flow tanks in the rad. I use them on all the vw's I own, I hate the gross looking white overflow tank. I retail them new for $160CAD if anyone wants one.
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My comment regarding the thermostat never opening was in regard to the fact that if thermosiphon were the motivating force as you say, then the Hot coolant would never flow *down* the bypass line to get to the thermostat to open it. Thus no flow. That is obviously not the case.
It is the case. Hot coolant never flows down the bypass line. Warm coolant is forced down by the pressure created by hot coolant coming out of the engine and also assisted by the water pump. The hottest coolant stays at the top. The thermostat opens fairly early in the coolant's heat load profile.
I understand very well the physics of thermosiphon. It just simply does not create the pressure differential to ever come remotely close to overcoming the force of the waterpump. I understand heated water rises in a water tank, but it doesn't jet above the surface to the the foce of the thermosiphon. The hot water pipe in my house then goes down the wall into the crawlspace and then to the faucets in the house. Again, I do get hot water at my faucets despite the fact that the hot water flows downhill in the pipe from the waterheater. The reason is because the force of thermosiphon is very very weak. It is dependant on the expansion of the molecules by heat making the substance lighter.
the hot water in your house pipe is not pressurized and is not beyond it's boiling point. The coolant in the car's cooling system is. This creates a strong thermosyphon that is assisted by the water pump. The main pumping action occurs at the base of the rad and into the bottom of the engine. There is a rather small amount of suction in the heater return line (look at a disassembled pump and you will see the hole is small and off centre). The pressure differential is stronger in the car's cooling system than in a house hot water system because the car's cooling system is under pressure due to the coolant being beyond it's boiling point and under pressure so it doesn't boil.
I will be installing an active solar panel water heating system on my house shortly. Even passive systems will benefit in efficiency from a circulating pump. Active systems where the panel is mounted above the tank require a pump to move the water against the thermosiphon effect. The pump does not need to be anywhere near as forcefull as the vw diesel waterpump to overcome the thermosiphon effect.
That is fine and true as long as the water isn't boiling. If it is, then the thermosyphon effect is huge. Look at nuclear electricity generation stations. The turbines are steam driven. There is no outside force that pushes the turbines, just super heated compressed steam. It spins those turbines and makes mega watts of electricity. All it is is boiling water under pressure.
Again, to go against the flow of the waterpump the coolant in the oil cooler line would need to be well above the boiling point to ever produce remotely enough force overcome the force of the waterpump pulling it in the other direction. *It's just physics*.
not really. Hot water always rises, so as the cool coolant gets warmed up in the oil cooler, it is going up. It is sucked up by the strong thermosyphon occuring at the top radiator hose.
I don't have time to get the hard figures on the force of the waterpump and the pressure differentials in the system. A pressure gauge at the inlet of the pump and the head outlet would show it. I also don't have time to look up the maximum pressure differential caused by thermosiphon. I merely present the info in hopes that your misinformation does not delude others. I'm done with this. If you want to still carry the torch and have the time, how about bringing back some test results regarding the pressure differential at the waterpump and what pressure differential can be achieved by thermosiphon. Short of some hard facts presented I am done with this conversation. I initially explained the coolant system much the way you do until, as I mentioned previously, I edjucated myself about it.
Well that is fine. But you must admit, even if you don't agree with my description of the mechanism, that the oil cooler does somehow manage to cool the oil and does not heat it. I know this because I have run vw diesels with and without oil coolers and measured the oil temp and the cooler reduces it. So it is in some magical way cooling the oil. It is also important as we all know that if you run a turbo on a 1.6 diesel that you have an oil cooler somewhere in the turbo oil line otherwise the oil will be too thin and wreck the floating bearing in the turbo.
I am *completely sure* (which is actually rare) that the results of any testing or further research would show that you are wrong. Again, *it's just physics*. I don't like beating a dead horse and will not repeat myself more.
I don't think so. If I am wrong then the oil cooler does not cool the oil, it heats it. That means we should all remove our oil coolers as they don't do any good. This is of course wrong. And I am keeping mine in place because I know it cools my oil.
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sounds like a plan. only thing i will add is that some early mkIs has non-overflow radiators... meaning they had a filler right on the radiator and no need for an expansion tank. if you want to clean up under the hood you could try eliminating the overflow altogether and see if you have any cooling problems. i have not done this personally (yet), but i have spoken with people who have, and despite their worry that the car would run hotter, in practice, it runs at approx the same temps.
I did that on a 79 rabbit diesel after cracking two expansion tanks. Got sick of replacing the things and got a rad out of a 77 rabbit with an internal expansion tank. It worked fine. No difference in cooling.
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The carburated VWs are the ones that came with overflow tankless radiators.
I run a carburated VW Radiator on my 1.6lTD for weight savings and to clean up the engine bay... no cooling system problems. But - without the clear plastic overflow tank, you can't as easily check the coolant level. What I usually do to do a quick fluid level check is give the upper radiator hose a squeeze. Can usually tell that way if there is coolant inside it and if the pressure is right.
fuel injected 77 rabbits had them too. That's where I got the one I put in my 79 diesel. You check the level by opening the rad cap and looking at this plastic rail that sticks out the side. The coolant should be at the top.
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The thermosiphon effect is not enough to matter in the compact, low volume cooling system of a modern engine. The pump pressure, whatever direction the VW engineers set up the coolant flow, makes it irrelevant. It may exist in harmony with pump flow, it may not, I don't know, it won't matter in an engine that has lost it's pump drive belt, it'll overheat anyway soon enough if you keep driving the vehicle.
Thermosiphon effect is enough to stir the water your hot water tank, so that it is evenly heated by the element at the bottom. It can move water thru a solar heating system - slowly. It circulates coolant in a motor that has it's freeze-plug engine heater plugged in on a cold winter night. It is not depended on for coolant circulation in a running engine, and can be easily overcome, even ignored,if the cooling system engineer decides to flow the coolant down instead of up.
I would not describe putting enough heat into a fluid to cause it to change state from a liquid to a vapor "thermosiphon effect". It certainly does not apply to an automobile engine cooling system, where that change of state must be avoided.
Steam turbines are not spun by thermosiphon effect. Look into Black's theory of Latent Heat. Steam power is all about the change of state, not hot water or steam rising above it's cooler counterparts.
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At some point I will add a temp sensors in the oil cooler circuit before above and below the oil cooler. I will report back when I do just for the "I told you so" factor. It may not be for quite a while as I have lots on my plate.
if you do that I think you will find that the coolant is hotter above the cooler than below it. Another interesting experiment would be to install some sort of flow direction device above the oil cooler to see what direction the coolant is flowing, perhaps a transparent tube with a plastic feeler inside of it that would move back and forth with changes to the flow direction of the coolant. I'll have to look around to see if I can get parts to build such a thing or if there is one readily available because I am interested to see if my theory is correct.
Regarding the poster from Alaska's comments, the coolant in the VW 1.6 diesel cooling system is under pressure. If it were not, it would boil and become steam. That makes the action of the thermo syphon in the cooling system of these cars similar to a steam turbine because the coolant in the cooling system is being restricted from undergoing a change of state, ie from liquid to gas. I know this is true because if your top cooling hose has a hole in it, which I have had happen to me, the coolant will escape as steam, and not liquid, meaning it is right at the point of change of state but not able to achieve that change because it is under pressure. This would create a strong thermo syphon, which is "assisted" by the water pump (that's how the bentley repair manual states it, "assisted", not driven by the pump. The pump assists the thermo syphon). Anyway I'll set up my experiment with a flow direction meter of some sort and then get back to you all with what I discover.
Chris
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Man, you are just so wrong. Thermosiphon is a function of gravity. It is not a matter of heated fluid exerting an upward force, it is a fuction of cooler denser fluid being acted upon by gravity to a greater extent than the slightly lighter, slightly expanded hotter fluid. Hot coolant still weighs close to as much as cold coolant thus the effect is minimal and as mentioned previously inconsequential.
As far as steam turbines are concerned, they develop their force because the system is open on one side to low pressure. Therefore the high pressure on the boiling fluid side pushes to the open low pressure side moving whatever is in it's way in the process. That has no bearing on the thermosiphon in a closed engine cooling system. The pressure created by the hot coolant is exerted on the entire system, including the colder side just as much as it is on the hot side. The pressure in the system would likely be detrimental to the thermosiphon effect as it would keep the hot coolant molecules closer together and thus closer in weight to the colder coolant. Thermosiphon BAH!
At this point it has become difficult for me to carry on this conversation without getting personal. I'm gonna quit.
hmmmm, perhaps you have some anger management problems there if you can't talk to someone with a different opinion than you without getting all hot about it. At any rate, gravity, as we all know, has nothing to do with mass. Any highschool physics teacher could tell you that. A feather falls at the same rate of speed as a concrete block in a vaccum. If you don't believe me, there is a simple experiment you can try. Hold a screw in one hand and a brick in the other, and drop both. You will see they both hit the ground at the same time. Gravity is not affected by mass, gravity is heavier objects exerting a force on lighter objects (Ie planet earth exerting a force on your screw and your brick). So the hot coolant and the cold coolant, despite being of different masses, are still subjected to the exact same gravitational pull and if that was the only thing acting on them, the hot coolant would not rise and the cold coolant would not stay at the bottom. What acts on the coolant is the expansion of the molecules, which causes the hot coolant to take up more space. Since space is limited, the hottest coolant moves to the top of the engine and through the top hose to the rad, where it is rapidly cooled, creating space in the rad for more hot coolant, which is being pushed in there by the expansion of the hot coolant in the engine. The same thing happens when a kettle boils and steam rises from it. The steam goes up because it is expanding into a gas (air) and there is not enough room for it, and the pressure it exerts on the air when it is expanding causes it to rise up through the air, because there is slightly less air as you go up (it gets thinner). It has absolutely nothing to do with gravity. If the radiator didn't cool the hot coolant, the expanded coolant would have nowhere to go and it would eventually burst a hose and escape as gas. The radiator does cool it though, and this creates the thermo syphon I was telling you about. That is why I find it hard, if not impossible to believe that hot, expanded coolant would flow downwards into an area of positive pressure (the bottom of the engine) when it had the option of flowing into an area of negative pressure (the radiator). It makes no sense that it would do that.
Anyway, try not to be too upset that I still don't agree with you.
Chris
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\It's like an argument over whether the earth is round or not.
:lol:
Or, if you really believe it, pull the water pump pulley and go for a nice long drive :lol: If you pay attention to the temp gauge, you most likely will have a chance to pull over and re-install the belt before you crack the head.
The problem is, the sillyness has taken away from the technical discussion about coolant flow. I'll search around and look for some diagrams.
EDIT: I looked into your previous posts, chrissev, and you seem like a smart person, a nice person ( who offered to help time someones engine for "gas" money ) - you've latched onto a process that, while it does exist, does not effect how coolant flow operates when driven by a pump. The system depends so completely on the existance of the pump that "hot coolant rising" DOES NOT MATTER - and in fact, some engines get designed with cold coolant from the radiator being pumped to the hottest part of the engine first, the heads, and then down and out the bottom.
You have some misconceptions. Perhaps another thread could be started with some of this information as a focus. I do recommend you try places like Wikipedia, search on steam engines, steam turbines, latent heat, etc.
a quote:
Thermosiphon
From Wikipedia, the free encyclopedia that anyone can edit.
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Thermosiphon (alternatively spelled thermosyphon) refers to a method of heat exchange through a phase change heat pump that depends on gravity. It allows the cooling and heating of objects by changing the phase of a liquid inside a closed system that relies on the principles of convection and gravity to move the fluid through the system.
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Why does oil float on water? Or more to the point why does anything float?
floating is to do with displacement. When something displaces more water than it's density, it floats. Oil does that because the molecules are farther apart when it is a liquid than are water molecules. Ships do that because they contain huge hollow areas inside of them that are filled only with air (and air isn't very dense). Hence why million ton ships can stay floating even though they weigh so much. If your theory was correct, every ocean liner would be at the bottom of the ocean right now.
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Wow now that winter's on its way its nice to find a real fire :twisted:
:shock: There seems to be some confusion here between vacuums and weightless environments... :shock:
Maybe its because there are few examples of weightlessness under atmospheric conditions. OK Ok training aircraft fairground rides etc. Conversely homemade vacuums under bell glasses are usually subject to gravity (my home is about 40 ft above sea level)
Anyway thermo syphoning does exist but it is small compared with pumped flow.
For example old central heating systems worked with thermosyphoning. New ones are not installed by the craftsmen of old who like my dad had a 7 year apprentiship. However new pumped systems will heat up quicker and pump hotwater up and down and round about.
Of course a system installed by my dad would work with or without a pump but the modern world dictates 1 year apprentiships and just a concern as to whether something works or not; and not its true quality.
Back to the rad problem the difference between hotwater and cold water (4deg) is its density. But the difference is only of the order of 4% or so at 107 degC and 1% at 50 deg C; so its not like throwing a rock into the sea!
If you guys can't stop biteing each other I'll have to ask you both to club together and buy me a rescued a/c system from a Quantum for Christmas
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let it go, man. The real issue is, for the purpose of this discussion, that the pump pressure is the one that counts.
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Gravity is in fact directly proportional to mass. That would be why the Sun (really big) exerts more gravitational force than planet Earth (relatively small in comparison).
This is true. But you need a really big difference in mass to notice any gravity at all. Ie a concrete block would exert a very small gravitational force on a feather, but you would never notice it. It would be too tiny.
Gravity is not "heavy objects exerting force on lighter objects". It is all matter exerting a force on all other matter. That force (gravity) is proportional with regard to mass and distance.
that may be true. No one other than Einstein has in my opinion given a satisfactory explanation as to how gravity works. He described it as objects distorting space and bending time. You should read his theories.
In a vacuum neither a feather nor a concrete block will fall. In fact in a vacuum there would not be a feather or a concrete block. If a feather and a concrete block were the only mass in an otherwise vacuum and they were stationary at the beginning of time, from that point forward they would accelerate toward each other until...
WTF? In a vaccum the feather and the concrete block would still fall. A vaccum is lack of any gas. That doesn't affect gravity. And a feather and a concrete block could definately exist in a vaccum. A light filament in a light bulb exists in a vaccum (no air in the lightbulb). Why not a feather or a block?
The acceleration rate of two objects toward each other *is* proportional to the *total* mass of *both objects*. The feather and earth will in fact accelerate toward each other slower than the concrete block and the earth even if "wind resistance" is the same. However, the difference is not noticeable to the human eye because the total mass of Earth+Feather is remarkably similar to the total mass of Earth+Concrete Block.
That is just plain wrong. Go back to physics class. The earth exerts the EXACT SAME gravitational force on every object that comes within its gravitational field. There is absolutely no difference for heavy objects and light ones. I wondered why I couldn't get you to understand me. Now I realize you don't have the fundamental building blocks of an understanding of simple physics. Also, the earth doesn't accelerate towards the feather. Hopefully you can see that at least.
The difference in acceleration of the concrete block and the feather is a prime example of the total effective force of thermosiphon in the VW diesel cooling system with regard to flow direction.
the only reason why the feather falls slower than the concrete block is because of air resistance on the feather. That is why I suggested doing the experiment in a vaccum. Anyway, do a simple experiment and you will see I'm right. Take a very small screw, a super tiny one, then the biggest brick you can find, and drop both from the same height at the same time. You will see they both hit the ground at the same time. That's how gravity works. It doesn't matter how heavy the thing is. Heavy objects fall at the same rate of speed as light ones.
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let it go, man. The real issue is, for the purpose of this discussion, that the pump pressure is the one that counts.
Isn't that what I've said?
Oops maybe that wasnt directed at me :lol:
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this is all very misleading.
hail falls quicker than rain, althrough they are both water, and yet hail weighs less but still falls quicker. how can that be possible?
think about that now, . the ability to overcome friction with the air is the limiting factor.
dropping a screw and a brick side by side from on top of a ladder or some such sillyless means nothing. both the brick and the screw will not have a chance to reach their own respective terminal velocity.
if it were possible to construct a feather with the shape of a really aerodynamic shape, say a laser guided bomb or somthing, that feather would probably fall really freakin quick.
but what does feathers and vacuums have to do with vw cooling systems?
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this is all very misleading.
hail falls quicker than rain, althrough they are both water, and yet hail weighs less but still falls quicker. how can that be possible?
think about that now, . the ability to overcome friction with the air is the limiting factor.
?
Does hail drop faster? Maybe the process of wetting the air slows it down... maybe its an optical delusion ;o)
Why dont hail stones abrade and form points as they fall and stick in the ground?
Doesnt the official line from VW state that the oil cooler is dual function? Remember these chaps were clever and designed doodle bugs on paper napkins (or were they all snapped up by the USA?) Perhaps VW was only left with the factory janitors which is why there are some obvious faults...
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let it go, man. The real issue is, for the purpose of this discussion, that the pump pressure is the one that counts.
The last vehical I've seen the relied on thermosyphon for the cooling was a 1943 John deere tractor. No water pump at all. And it takes 3" water pipes to get the required flow to cool an 18 HP engine.
Given this design, I don't think the thermosyphon does much on a VW rabbit.