can anyone explain how the funny vw cooling system works?

[chrissev]

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.

[deepmud]

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.

[chrissev]

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

[chrissev]

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

[deepmud]

\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.
Jump to: navigation, search

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.

[chrissev]

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.

[Mark(The Miser)UK]

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

[deepmud]

let it go, man. The real issue is, for the purpose of this discussion, that the pump pressure is the one that counts.

[chrissev]

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.

[Mark(The Miser)UK]

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:

[Master ACiD]

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?

[Mark(The Miser)UK]

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...

[zyewdall]

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.