afterrun coolant pump

Bernie Benz b.benz at
Fri Oct 2 19:53:36 PDT 2009

#3 retort.

If you need a new pump, the current A4, 6, 8 pumps are a better and  
P&P design and cheaper, BTDT.

Most oxides of iron are non magnetic. Magnets are an old Audi wife’s  
tale! Can’t hurt much, but the wallet. Detergents are only useful if  
there is oil in the cooling system.  Citric acid is a joke in an  
aggressive attack against iron oxide accumulations.
Better if mixed with rum. But why the accumulations? Running tap  
water or not changing antifreeze at end of life? Better, use oxalic  
acid, the active ingredient in commercial radiator flushes, available  
cheap in full crystalline strength from your local paint store, ask  
for wood bleach.


On Oct 2, 2009, at 4:14 PM, Brett Dikeman wrote:

> On Fri, Oct 2, 2009 at 11:35 AM, Gsidman <gsidman at> wrote:
>> On the '91 200 20v the coolant pump and the fan should come on  
>> couple of
>> minutes after shutting off the engine, and both should shut off
>> automatically after a few minutes.
> The 20v's rarely run the afterrun circuit.  My 5kCST would run it all
> the time, but the 10v is not crossflow, and the 20v has the aux
> radiator circuit, improved fan, etc.  If you want to make sure
> everything is healthy:
> 1)Replace the switch, it's not expensive, I don't think.  Or put it in
> a soup can on the stove and see when it closes.  Make sure you get the
> right part number etc.
> 2)Short the switch terminals together, see if the fan runs (if so, the
> relay is OK.)  There is no built-in time delay, if the switch is open,
> the relay trips immediately.  It has a
> keep-the-battery-from-going-dead timer on it, and the timer is reset
> every time you turn on the ignition.
> 3)REMOVE the pump and make sure the rotor spins.  It is magnetic
> drive, so bits of rust fill up the space between the rotor (which is a
> permanent magnet) and housing, jamming it.  Soaking it in citric acid
> may help.  Future maintenance?  Well, get two small neodymium magnets
> and put them on either side of a radiator tank or something.  I
> guarantee neither one will go anywhere- I've got a set and they'll
> stick to each other through an inch plus of wood; watch your fingers,
> they WILL cause bodily harm, as well as shatter sending crap flying if
> they, say, roll near each other on a table and snap together.  They
> will attract ANY rust in the system, rather than your expensive pump.
> I used to get the gurgling noise all the time, too.  Never found a
> fix, really.  One thing you can try is flushing the system- use Shout
> (buy it in the big bulk container) to degrease, then citric acid
> (available at MB dealerships, possibly restaurant supply places,
> definitely online.) See all that crap in the expansion tank?  That's
> everywhere else, too, preventing heat transfer.  Run the blue pentosin
> coolant, with distilled water.
> The MB guys seem to swear by the Shout and citric acid combo.  Any
> low-suds detergent will work, by and large, just make sure you
> COMPLETELY flush it out.  Also, you can switch to the latest Audi
> coolants, just gotta flush all the old stuff out...
> Brett
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