afterrun coolant pump

[Brett Dikeman]

On Fri, Oct 2, 2009 at 11:35 AM, Gsidman <gsidman at webloq.com> 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