[V6-12v] Radiator Fans not switching in correctly...

Wed Sep 6 14:10:19 EDT 2006

Well, I have another layer to add to the mystery. The car has been in the
local garage for the last couple of days with them trying to figure this one
out! They've eliminated a fair bit, and come up with a tentative conclusion,
but aren't really sure, so I thought I'd run it past your collective Audi
brains!

They first tested the fans. They think these are working correctly, but that
the temp of the rad wasn't getting high enough to trip the thermo switch in
to the first stage (so what I was hearing WAS the first stage, although I
was seeing a much higher block temp from the temp sender than I normally
would for 1st stage fans, if that makes sense.

This led them to examine the rad and find that the top 1/3 of the rad wasn't
getting hot. Conclusion: blocked rad, right?

Well, maybe. Because the rad is an expensive replacement part, they kept the
car in today to do a flow test (basically pouring water in the top and see
if it comes out of the bottom at a good flow). Well, it did flow pretty
well, certainly not completely blocked.

This stumped them a little, so they put the rad back, drained the coolant (a
bit of gunge did come out, apparently) flushed and re-filled. But here's the
puzzler:-

When they restarted the car, it came up to temp, and heated right to the top
of the rad. Then the cooling fans kicked in, and the top of the rad went
cold again and now it's back to where we started!

So the mechanic doesn't know what it is now. He's still betting on a
partially blocked rad, but that doesn't explain why it heated properly to
the top, then 'blocked' again.

He even tested the coolant with a CO probe to see if the head gaskets were
leaking air into the system causing an air pocket at the top of the rad, but
there was no trace of air or exhaust gas.

Lastly, he wondered if the water pump plastic impeller (are they plastic on
this model?) had broken and wasn't working properly when up to temp, or
whether a bit of this plastic was blocking something.

For my part, since I know the thermostat was on it's way out, I wonder if
it's just completely gone and is shutting off the water to/from the rad...

Anyone got any ideas given those particular symptoms? At the moment I'm
leaving it til I do the head gaskets in about 14 days time, as it's still
driveable, and I'm replacing the thermostat, water pump, etc as a part of
that job anyway...

Any thoughts appreciated!

Cheers,
James

> -----Original Message-----
> From: Wilfried Link [mailto:wilfriedlink at yahoo.com]
> Sent: 03 September 2006 05:46
> To: Poncho; Tom Christiansen; James Whitehouse
> Cc: v6-12v at audifans.com
> Subject: Re: [V6-12v] Radiator Fans not switching in correctly...
> 
> I had similar problems with my 95 A6. Turned out all
> switches and relays were fine. The cause was one of
> the electric cooling fans was worn out -- the carbon
> brushes on the motor just plain too short to
> consistently make it run. After replacing it,
> everything worked fine again. About a year later, the
> other fan motor stopped working as well. Replace it,
> all is well again. The car had about 190,000 miles on
> it. If you can find a shop that will replace the
> brushes, consider that option -- the brush contact
> area was too worn on mine, but the new fans vibrate
> noticeably when compared to the silky smooth original
> ones.
> 
> Wil
> 95 A6 Avant
> 
> --- Poncho <ponchojuan66 at yahoo.com> wrote:
> 
> > SOunds like its running correctly.  The sensor on
> > the
> > raditor is actually a switch to control the fan (
> > through the resistor block).  This is configured
> > differently on depending on number of issues.
> >
> > Normally the fan will come on when the temp guage
> > reaches just ubove top dea center on the guage.  It
> > will typicallu stay on for a fe mimutes and shut
> > off.
> > You will not notice much movement in the guage.  The
> > reason is the water is cooled in the radiator and
> > the
> > guage "sensor" is the one on the heater hose behind
> > the engine.
> >
> > The whole thing is working IF the you keep the car
> > idling and it stays around the middel of the guage.
> >
> > Under way ( 30MPH or more) , it should eventually
> > return to the 1/3 mark.  IF you don't trust it, you
> > can check the temp witha a meter a temp probe.  But
> > I
> > would not worry too much.  Aslo make sure you are
> > running the right mix of antifreeze and the
> > expansion
> > cap is ok.
> >
> > poncho
> >
> > --- Tom Christiansen <tomchr at gmail.com> wrote:
> >
> > > Marc, James:
> > >
> > > The external thermometer is a completely different
> > > circuit. The sensor
> > > is located behind the lower grille by the port
> > side
> > > foglight. It's a
> > > NTC resistor. It's resistance at ~70F/20C is
> > roughly
> > > 1500 ohm (easily
> > > verified with an ohmmeter). It has a 2-pin
> > connector
> > > that's wire-tied
> > > to the bottom of the battery 'shelf'. From there,
> > > the wires go via the
> > > fat wiring harness into the instrument cluster,
> > > where it ends up as
> > > pin 2 in the connector for the thermometer
> > display.
> > > It's the brown
> > > wire with a yellow stripe. Measure the resistance
> > > from that
> > > yellow/brown wire to ground and you should get
> > 1500
> > > ohm at 20C/70F.
> > >
> > > The reason I know is that that wire got pinched to
> > > ground when I
> > > replaced the heater core. I recently ran another
> > > wire to get the
> > > display to work. It was showing 'E' all the time.
> > > Drove me nuts...
> > >
> > > Aside from the 'E' in the display I noticed no
> > > ill-effects of having
> > > that wiring messed up.
> > >
> > > Tom
> > >
> > > On 8/29/06, James Whitehouse
> > > <james_whitehouse1 at yahoo.co.uk> wrote:
> > > > Marc,
> > > >
> > > > It's a valid question, but I don't know what
> > > sensor reads the outside temp -
> > > > which one are you thinking of, and how would I
> > > check whether it's accurate?
> > > >
> > > > Thanks for the zinc paste info!
> > > >
> > > > Cheers,
> > > > James
> > > >
> > > > > -----Original Message-----
> > > > > From: The CyberPoet
> > > [mailto:thecyberpoet at cyberpoet.net]
> > > > > Sent: 29 August 2006 20:42
> > > > > To: James Whitehouse
> > > > > Subject: Re: [V6-12v] Radiator Fans not
> > > switching in correctly...
> > > > >
> > > > > here's some more info on those zinc-suspension
> > > pastes:
> > > > > http://sw-em.com/anti_corrosive_paste.htm
> > > > >
> > > > > Q: are you getting a valid reading from the
> > > outside temp sensor? If
> > > > > it's reading way too low or not at all, it
> > might
> > > affect the system
> > > > > logic for the fans...
> > > > >
> > > > > Cheers
> > > > > =-= Marc
> > > > >
> > > > > On Aug 29, 2006, at 1:13 PM, James Whitehouse
> > > wrote:
> > > > >
> > > > > > Marc,
> > > > > >
> > > > > > Thanks for that, I'll try cleaning the
> > > connector on the radiator-
> > > > > > mounted
> > > > > > thermo switch first. I don't have any
> > > knowledge of anything similar to
> > > > > > 'Nolox', but I use DeoxIt as a contact
> > cleaner
> > > often and it seems
> > > > > > to work
> > > > > > OK. If that doesn't help, I'll probably try
> > > replacing that thermo-
> > > > > > switch
> > > > > > first, followed by the 'radiator fan 1st
> > > speed' relay in the fuse
> > > > > > box -
> > > > > > they're not expensive parts.
> > > > > >
> > > > > > If anyone else has any more info/ specs on
> > the
> > > system, please let
> > > > > > me know,
> > > > > > I'd be grateful for any fault finding
> > > procedures, etc.
> > > > > >
> > > > > > Cheers,
> > > > > > James
> > > > > >
> > > > > >
> > > > > >> -----Original Message-----
> > > > > >> From: The CyberPoet
> > > [mailto:thecyberpoet at cyberpoet.net]
> > > > > >> Sent: 28 August 2006 12:22
> > > > > >> To: James Whitehouse
> > > > > >> Cc: v6-12v at audifans.com
> > > > > >> Subject: Re: [V6-12v] Radiator Fans not
> > > switching in correctly...
> > > > > >>
> > > > > >> This isn't my area of expertise, but I do
> > > know that on my V6's (at
> > > > > >> least based on my experiences), the
> > following
> > > seems generally true:
> > > > > >>
> > > > > >> (A) There are two electrically-driven fans,
> > > the primary one triggers
> > > > > >> on temp of the radiator temp sensor, and
> > the
> > > second of which triggers
> > > > > >> based on air conditioning use (as well as
> > > kicking on at a higher
> > > > > >> thermal level threshold for the
> > > radiator/engine).
> > > > > >>
> > > > > >> (B) The wiring connectors for the sensors
> > is
> > > often the first thing to
> > > > > >> go bad, because of exposure in my
> > experience.
> > > Cleaning the contacts
> > > > > >> thoroughly & dielectric grease is often the
> > > best place to start.
> > > > > >> Sidenote: I've found a dielectric grease
> > > called Nolox that contains
> > > > > >> zinc particles in the suspension which
> > forces
> > > a fresh cut through
> > > > > >> surface corrosion on connectors every time
> > > the plugs are mated works
> > > > > >> better than traditional vasoline-like
> > > dielectric grease if there is
> > > > > >> already a problem with connectivity. There
> > > are Brit-market
> > > > > >> equivalents (I selected Nolox because all
> > the
> > > other options were UK-
> > > > > >> based and not readily available here). This
> > > is not a total solution
> > > > > >> for bad connectivity, but given a connector
> > > that already had to be
> > > > > >> cleaned of surface corrosion once, I'll
> > grab
> > > the nolox just to
> > > > > >> improve the situation in the future (such
> > as
> > > plugging/unplugging tail
> > > > > >> light connectors on the road where I don't
> > > carry a full toolkit with
> > > > > >> sandpaper, etc. with me)...
> > > > > >>
> >
> === message truncated ===
> 
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