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Discussion Starter · #1 ·
I know this subject has
been covered numerous times before by other how-to fix your fans guides, but as
they all seem to have been forgotten by now I thought I'd bring it up to date
with this guide on how to solve a problem a lot of mk.4 owners might not know
they're suffering from.

This can potentially affect
all mk.4s with any type of air conditioning. Manual air con with the normal 3
rotary dials with two buttons underneath them, and climate control with all
push buttons and the digital display. How it should work is that both fans
should run constantly at low speed all the time the air con is switched on, and
only work at full speed when the engine gets too hot such as when sitting in a
queue of traffic for a long time. The low speed is done through a 1 Ohm
resistor built into the case of the motor, but because of poor quality
components and inadequate cooling, these resistors burnt out even on cars as
new as just two years old. Not only are the fans needed to keep the air flowing
over the air con condensor when the car is stationary, they also keep the air
con pump cool. Very important on the V6 engines is that they also keep the
alternator cool which suffer from premature failure compared to alternators on
four cylinder engines which have much better air flow through the engine bay.

This is the brush plate
from the larger of the two fans. The low speed resistor is the crescent shaped
white ceramic component at the very bottom of the photo……



And this is what causes the
problems that we're all suffering from…….



It could actually be
repaired if you really wanted to. Not using normal solder though as this could
get hot enough in use to melt solder. It would either have to be brazed, spot
welded or crimped with a very small piece of brass tube.

How to test to find out if
your radiator fans are working as they're supposed to……..

1………..Start the engine and let
it idle

2………..Turn the air con on
normally,so NOT on ECON.

3………..Make sure both fans
run constantly at low speed. The most common symptom of resistor failure is
that they pulse on and off in roughly a 20 second cycle,or they run at full
speed for a couple of minutes and then stop working all together.

If they don't come on at
all, this could be a fuse (the middle
one of the five fuselinks on top of the battery or the green 30 amp blade fuse
closest to the middle of the car),a faulty fan control module (underneath the
battery tray) or a faulty fan switch which can be found towards the bottom of
the radiator near the battery tray. Hopefully you'll be lucky enough not to
have to replace the fans themselves and will be up and running again with just
the external resistor mod.

This circuit diagram shows
how the cooling fans are wired, the dreaded low speed resistor is shown circled
in red. As you can see, they're wired in parallel so should both run at the
same time at the same speed…..



We don't HAVE to cut the
red/white wires like this as there's effectively nothing on the other end of
them now, but better safe than sorry as they say……



This is how we connect up
our new external low speed resistors……



The rest of this is more or
less echoing what the previous guides have all said, with the exception of
making the connections. I have seen Scotchlocks and even domestic "choc block"
style connectors recommended for this job. Neither of these are in the least
bit waterproof which is essential for a job like this, so please solder the
connections if you possibly can if you don't want to be doing it all again
every couple of months when the fans stop working again. Decent crimps don't
with a proper ratchet crimping tool ( NOT the pliers type) would also work
here, but they should be as tightly wrapped as possible to waterproof them with
heatshrink sleeving or self amalgamating electrical tape.

Here's a list of parts we
need for this job……

1…………Print out the template
for the mounting plate from this link…………http://website.lineone.net/~alan.james.lorely/fan%20mod/Repair.html

2…………A couple of 1 Ohm 100
watt resistors like these………http://uk.rs-online.com/web/p/panel-mount-fixed-resistors/0188087/
(You'll need an account to order from RS though)

3…………Some 2 to 3mm thick
aluminium plate.

4………..A couple of metres of
any colour wire capable of carrying 15 amps or more. The low speed current draw
is only 7.5 amps but this gives us a nice safety margin.

5………..3 X 5mm (or 6mm)
bolts about 30mm long with nuts and washers.

Cut the template out and
stick it your ally sheet with spray glue or similar……



Cut roughly to size with a
jig saw……



Never ever use the jaws of
a vice like this as sawing guide when trimming it to it's final size. You're a
bad man if you do!





Centre punch through the
paper for the positions of the holes and drill to the sizes marked on it.



Solder the wires to your
resistors like this. There's about 7.5 Amps flowing through these continuously,
so use any wire that will handle above 15 amps just to be 100% safe.



Apply a SMALL amount of
heat sink compound to the base of the resistors…..



Pop rivet or bolt them onto
the plate……..



Put M5 bolts and nuts
through the existing holes in the chassis plates……



It should fit like this
when you bolt the resistor plate up to it……



I find it easier to undo
all three plugs, the two to the fans and the one to the fan control module as
shown here…..



This is the fan side of the
wiring, the one to the left is for the big fan and the one to it's right is for
the smaller fan. The one above them is the fan switch/sensor.



The next bit is where some
people do this differently. They make the connections on the other side of the
above connectors in the actual wires to the fans. This works just as well
electrically, but it means if you ever need to change the fans in the future,
you'll need to get the soldering iron out as well. My method means any future
fan changes will be 100% plug-and-play.

Cut the red and white wires
close to the plugs (we won't be needing the plug end of these wires any more)
and solder one wire from each resistor to the red and white wires from the fan
control module….





Splice the wires from the
other ends of the resistors into the thicker red/black wires. Try to get them
the right way round if you can, but it's not all that important as they're
wired in parallel.





Tape up or heatshrink the
joints and loom the wiring up neatly using tape or small cable ties, maybe use
a P clip where it crosses underneath the chassis rail. Plug everything back in
again and make sure you hear them click, the fan control module plug in
particular needs a LOT of effort to get it all the way in.



Start the engine and let it
idle. Turn the air con but NOT on econ and make sure that both fans run
continuously at low speed and only switch off when you turn the air con off.
Also maybe let it warm up fully and make sure the fans work at high speed once
the engine gets to the point of starting to overheat.

If they switch on and off
as they're supposed to, make sure the various arch liners and undertrays have
all their fastenings in place and put the bumper back on.
 

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As always , an excellent guide, very easy to follow.
 

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Hi

I'm a newbie who's just brought a V6 4MOTION (after loving my VR6 a few years ago), and notice I have this issue, and aiming to fix next week.

Great guide @Imagewerx I look forward to using it!

A few qestions;

  • Do you need to remove the front bumber and headlight to complete this job?
  • I presume once fixed, the hi speed fans will still work when required?

Cheers

Pat
 

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Hi

I'm a newbie who's just brought a V6 4MOTION (after loving my VR6 a few years ago), and notice I have this issue, and aiming to fix next week.

Great guide @Imagewerx I look forward to using it!

A few qestions;

  • Do you need to remove the front bumber and headlight to complete this job?
  • I presume once fixed, the hi speed fans will still work when required?

Cheers

Pat
You could take the wheel off and remove the arch liner,but it'd be like painting your hallway through the letterbox connecting the wires up.It'll be quicker to remove the bumper and do it the easy way,you won't be saving any time by not taking it off.

And yes,all the fan functions will be 100% as they're supposed to be.
 

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Hi

I have a Bora V6 4Motion (2001) and have been living with this problem for a while. I've been doing limited mileage in the car, haven't been using Aircon and the 40amp fuse above the battery hasn't gone yet (therefore I still have my main fan pulsing on high speed), so haven't been in a rush to fix it. I know it's only a matter of time before the 40 amp fuse goes causing my main fan to stop working and risking an engine overheat. So I'd like to get it fixed.

I'm not a car mechanic and have limited time to do stuff like this so I just wondered if anyone was in a position to build and fit one of these mods for me and if so what it might cost? I'm in the Brighton area.

Also, I don't think this has been covered in the FAQ's and I haven't found an answer to it.

Q). If I don't use Aircon (and don't plan to) - i.e I always leave it turned off completely or use it on Econ, should I be worried that the low speed doesn't work? i.e the post clearly states that slow speed should be on (when aircon is on) to protect aircon pump, condensor, alternator (on V6 cars) etc. When you turn aircon off, slow speed stops. So if aircon is turned OFF how does normal engine cooling work? When the engine gets up to a high temperature does it spin the fans on high speed for a bit or is it a bit cleverer and tris to use the fans in slow speed for cooling?

Basically - if I never use Aircon then should I care about the lack of slow speed operation?

Regards

Dan
 

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Discussion Starter · #12 ·
The fan should only work on the higher speed when the engine starts to overheat,when driving the car air is forced through the radiator by the forward motion of the vehicle. It won't be needed and should never come on all the time the car is in motion,if you're stuck in traffic for more than about 10-15 minutes,then it should come on until the engine has cooled down.
 

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And am I right in thinking you must run the aircon from time to time regardless of whether you want it, to get the gas circulating lubricant to all the seals, and ensure the system doesn't develop leaks?
 

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Discussion Starter · #14 ·
And am I right in thinking you must run the aircon from time to time regardless of whether you want it, to get the gas circulating lubricant to all the seals, and ensure the system doesn't develop leaks?
Yes you are correct,at least once a week even in the winter run it for about 5 minutes or so.
 

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Hi Chris. My high speed fans don't kick in at all. Low speed fans run constantly ok with aircon on...no pulsing or stopping etc. Would this mod help ? Also my aircon compressor doesn't actually kick in work (maybe clutch or switch is faulty), so I'm not sure if compressor not working is linked to high speed fans not working ? Any help would be gratefully received !
 

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Would anyone know the resistance, current rating or wattage of the individual fan motors, big and small?

Bothe resistors have gone in my car tested it today :( having a nightmare with this car..

cheers, Huw
 

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You need 2 of these as per Chris's excellent post, further up the page.

I bought 4 from RS so may have 2 you can buy off me, just need to check.

…http://uk.rs-online....istors/0188087/

Alex
 
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Ok I found them, are you interested, if so I will find out the postage as they are quite heavy.They weigh 200 grammes on their own...
 

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Excellent guide gents. Thanks to your help,pics and information another 4Mo V6 is on the road with working low speed cooling fans. Cost about £20 for the parts and some hours of my time to get it all back up and running.

Chances are the low speed fan function has been broken since the early days as looking back through the receipts and history of my 4Mo, it has required 3 alternators!!
A couple of pics for no reason other than I want to. I didn't have stainless steel thick enough, but I'm willing to take a chance on that and I'm certain it cannot be worse than the resistors inside the fans :)

IMG_4220.JPG


IMG_4222.JPG


IMG_4221.JPG
IMG_4223.JPG


IMG_4225.JPG
 

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Discussion Starter · #20 ·
. I didn't have stainless steel thick enough, but I'm willing to take a chance on that and I'm certain it cannot be worse than the resistors inside the fans :)

IMG_4225.JPG
I used aluminium and not stainless on mine.It really doesn't make a lot of difference in terms of getting rid of the heat,but the ally is a LOT easier to drill holes in than stainless is.

Oh and the wire by itself in that last photo should really be loomed up with the other three and secured to the chassis somehow,it'll vibrate and probably crack and break the solder joint having it loose and unsupported like that.
 
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