I apologize in advance for anyone who is bothered by pedantry.  You don't have to read it.

Of course you are correct, Alistair.  But, embedded in the imprecise language is a kernel of value.  When a solution like coolant, which has a higher viscosity than does water, and may also contain some materials leached or eroded from various metal components of the coolant system, sits in a stagnant state, it is more likely to precipitate some of those materials creating a greater likelihood of plugging small passageways than when it is flowing.

I clearly demonstrated this when I had a pump go out on a dishwasher just when I was leaving for a three week trip.  I just left the water, with detergent and crud in it, in the dishwasher.  When I returned, I had to replace more than the pump.  The screens and chopper blade were plugged and had to be replaced as cleaning them did not work, though I used a concentrated citric acid solution.

BTW, what is usually called a knob in mechanical applications where it serves as a handle to transfer a circular motion is in fact a kind of lever.  An easy way to visualize this is to imagine that a door knob is reduced to a rectangular piece running across its diameter.  Then cut off one radius of the piece.  What you have is a lever such as has become popular for home doors to reduce strain on hands and wrists of older folks.  Many knobs are constructed with a rectangular piece running across one diameter to serve as a handle to make grasping easier.  That in fact is what the valve on the rear heater has.  This also demonstrates the fact that a knob is simply a lever acting to apply torque.

mcneely

---- Alistair Bell <albell@SHAW.CA> wrote:
> "old coolant is terribly corrosive"
>
> come on now, how is coolant that is not circulated any older than the stuff that is circulated. I call bull-pucky.
>
> alistair
>
> On 2012-11-18, at 1:50 PM, Scott Daniel - Turbovans wrote:
>
> > There is no 'control knob' ..
> > there is a lever that you can reach with your fingers, through a hole in
> > the rear heater cover.
> >
> > if the cover is not in place...the poster could be looking at a
> > knob-like thing ..the bleed valve.
> >
> > Bentley would not say much about this leverthat regulates coolant flow .
> > but the van's Owner's Manual sure does.
> >
> > 'Forward' on the lever is 'on'.
> > Aftward is off.
> >
> > I recommend having it at least mostly 'on' all year ..
> > as having no flow at all, ever, or for very long periods ,  contributes
> > to rear heater core leaking ..
> > a pretty common thing actually. .
> >
> > Whether warm air comes out the rear heater is determined by the fan for
> > the rear heater being on or not, or course.
> >
> > you always want at least some coolant flowing through the rear heater so
> > some fresh healthier coolant is always going through it ...the parts
> > last longer that way.  Old coolant is terribly corrosive.
> >
> > Nobody on this list of course...
> > there are lots of vanagon owners that don't know about the heater
> > control lever under the back seat.
> > I was kinda shocked actually to find out VW did it that way.
> > I can't think of one other car that has a partially heater control under
> > the back seat.
> >
> >
> >
> > On 11/18/2012 11:49 AM, Dave Mcneely wrote:
> >> Harry, that control allows coolant to circulate through the heater core.  Summer, off, winter, on.  To control air flow, use the knob on the dash.  mcneely
> >>
> >> ---- Harry Hoffman <hhoffman@IP-SOLUTIONS.NET> wrote:
> >>> Hi all,
> >> The heater under the rear seat has a control knob.
> >> Can someone tell me what it does? The Bentley only shows a picture but not how it functions.
> >>
> >>  Cheers,
> >> Harry
> >>
> >> --
> >> David McNeely
> >>

--
David McNeely