Fusing the fan?

alan cordeiro alancordeiro at comcast.net
Tue Sep 21 22:41:25 EDT 2004

Fuses are intended to provide two types of protection,

a) They protect the electrical apparatus from drawing sufficient
     power to catch on fire in the event of an internal fault. All
     electric products go through rigorous testing to ensure
     any type of internal fault will not cause it to catch on fire
     as long as the RECOMMENDED fuse is used on the power
     supply side.
b) They protect the wiring to and from the device from overheating
     to the point where the insulation could be damaged, and possibly
     could cause a short or start a fire.

IMHO the 80 amp fuse sounds way too large for the wiring there,
I would hesitate to replace it with anything larger than a 40 amp fuse
Remember, a 40 amp fuse will comfortably take 50 amps for a short
while, even twice the current for a few seconds (typical fuse, slow-blow
or medium blow fuse, not the very fast fuses designed to protect

I remember the original fuses can be obtained from your friendly
dealer for a few $ each...and last many years. Why bother with
guessing your own??


----- Original Message -----
From: "Ben Swann" <benswann at comcast.net>
To: "Hoffman Anthony J A1C 552 CMS/MXMVC" <Anthony.Hoffman at tinker.af.mil>;
"Ti Kan" <ti at amb.org>
Cc: "Terhune, Patrick" <pterhune at firstservicenetworks.com>;
<quattro at audifans.com>; <200q20v at audifans.com>
Sent: Tuesday, September 21, 2004 8:28 PM
Subject: Re: Fusing the fan?

> Great info Ti!  I should have read through the 100 or so posts I have in
> inbox before asking the question that this seems to answer.  Just
> reiterating your post for continutity as well as passing it on.
> 80 AMP Fuse!  WOW!  That is a lot.  Isn't all this current passing through
> the fusebox?  Or is there just the low speed circuit that goes through the
> wiring at relay position 2?
> I simply inserted some spade lugs and inserted the fuse into them and
> insulated the lugs and mounted on the fan frame.  I would guess there are
> many variations on this.  So maybe the 60 AMP fuse I have in there now is
> not overkill and I should have expected the 30Amp fuse to blow - it didn't
> right away, but did eventually.
> Ben
> ----- Original Message -----
> Hoffman Anthony J A1C 552 CMS/MXMVC writes:
> > How have some of you fused the fan? I have two 5000's recently acquired,
> and
> > would like to do this. What amp rating is required?
> Below are a quotes from several related posts in 1999 on this list.
> -Ti
> --
>  R 1 3 5  Ti Kan
>  |_|_|_|  http://www.amb.org/ti
>    | | |  Vorsprung durch Technik
>    2 4 6
> ------------------
> Cooling Fan Fuse Modification
> In addition to their many excellent qualities, the 5kt/q (type 44) cars
> well known for their
> tendency to incinerate the left main engine compartment wiring harness
> the cooling fan
> seizes. There is usually a warning squeak from the fan bearings giving the
> owner between 2 hours
> and 2 months advance notice of impending doom. See the past "Audi
> thread, for example.
> There have been several solutions presented on the list, but I feel the
> thoroughly engineered fix
> has been one designed by Audi. A neatly housed and mounted 80A fusible
> was incorporated
> into the USA 200s at some point(?). I first noticed this fix in a 1991
> Fortunately, this modifi-
> cation is as easy as pie for any type 44.
> The parts list: (Audi P/Ns are given for the hardware, but you can always
> eyeball this and
> use whatever you sweep up off the garage floor.  I ordered this stuff from
> Carlsen when I bought
> the box, bracket and fuse; for the extra $2, you can get it exactly right.
> BTW, your Carlsen
> prices should be lower than Retail.)
> Qty.    Item            Audi P/N        Retail $
> -------------------------------------------------
> 1       fuse box        281 937 505 A   10.89
> 1       bracket         443 971 845 AM   9.55
> 1       fuse link, 80A  N 017 125 3      1.30
> 2       screw, M5x8     N 014 128 11     0.45
> 2       lock washer     N 012 005 3      0.15
> 2       screw, tapping  N 013 966 26     0.38
> 2       washer, flat    N 011 556 2      0.15
> Other materials:
> 1 foot  10 AWG wire for automotive service, preferably
>         brown to match the European color convention.
> 2       crimp terminals, 10-12 AWG (yel.), #10 ring
> 1       crimp terminal, 10-12 AWG (yel.), 1/4" ring
> 3-4"    shrink tubing, 1/4" to 3/8" diam. (optional
>         for insulated crimp terminals)
> 1 or 2  cable ties (optional)
> Tools: 10mm wrench, medium Phillips screw driver,
>        high quality crimping tool appropriate to selected
>        terminals (perhaps borrowed), heat gun, wire
>        stripper.
> Procedure:
> Notes.
> a. It is proper to disconnect the battery before undertakingany wiring
> modifications. However, if the engine is
> STONE COLD and if you email me a signed liability waverin advance, it is
> possible to proceed with reckless
> disregard for safety and leave the battery connected since the effected
> wiring is strictly ground side.
> Keep the wrench away from the positive fan motor terminal and your face
> clear of the fan blades just in case I'm a
> lying dog.
> b. It is assumed that you know how to properly fit crimped wire terminals
> and have the proper tool.
> Soldered joints can be used but are emphatically not recommended for
> automotive wiring connections
> for the best long term reliability. However, if you don't have access to a
> _good_ crimping tool, soldering may be the better choice. A cheap, single
> acting "electrician's"crimper will definitely not provide sufficient
> pressure
> to correctly crimp such heavy terminals. (I'm not interestedin a crimp vs.
> solder or crimp vs. solder & crimp thread.
> Just suit yourself and take your best shot.)
> c. The fuse link box has two link positions. This fan motor circuit only
> uses one of them. Please don't swoon
> and hurt yourself while contemplating the infinite possibilities.
> d.  I haven't looked at every type 44 model. Details could certainly vary.
> Determine if the following
> instructions make sense for your vehicle before starting so you will have
> been able to work out any necessary
> corrections ahead of time. Easiest to do with partsin hand.
> 1. Establish that the shrink tubing, if used, is sized  to fit the
> crimp terminals. Mandatory for
>    uninsulated terminals.
> 2. Mount fuse box to fuse bracket with tapping screws  and flat washers.
> suggest mounting so that
>    the hinge of the cover is up^ in order to better   resist water entry.
> would be a good idea to
>    test fit the bracket in the car first just so   that it is completely
> obvious which end   will be "up" and that the bracket's mounting   tab or
> ear bends away from the surface the box   is attached to.)
> 3. Remove the right-rear mounting screw from coolant   reservoir. This
> also retains a mounting
>    clip for the left-front ABS sensor connector   and a small aluminum
> wiring harness support "Z"   bracket.
> 4. Remove this aluminum "Z" bracket (for ABS unit   wiring harness) after
> releasing the plastic wire
>    clip from "Z" bracket hole. Leave plastic clip on   harness. Throw "Z"
> bracket into the "save for use
>    in next lifetime" bin.
> 5. Mount bracket/fuse box. The stacking order is new   fuse box bracket,
> then ABS connector clip, then
>    coolant reservoir tab. This all goes together   nicely like bread and
> butter. The fuse box
>    now faces the engine.
> 6. Leave the dangling ABS wiring clip unattached   until the wiring is
> complete. Be comforted
>    by the fact that the new fuse box bracket has   a hole just the right
> size and in just the right
>    place to accept the clip nibs. (Ya just gotta   love German engineers
> times like this.)
> 7. Remove the cooling fan motor's ground lead (single   heavy brown wire).
> 8. Cut off (oh go ahead) the terminal on this lead   since it ought to be
> replaced by a smaller size
>    ring to match the fuse box screw size. You shade   tree electricians
> might spit at this but I really
>    think it necessary for a good installation. Cut   the wire as close to
> the terminal as possible to
>    allow good reach with the remainder.
> 9. Install a #10 ring terminal (metric size 5 mm?)   on this fan motor
> ground lead. Slip a piece of
>    shrink tubing on beforehand to avoid that stupid   feeling. Carefully
> apply shrinking heat.
> 10.Bend the ground wire back toward the new fuse box and   loosely connect
> this terminal to one of the forward-most   box screw terminals. Use a 5Mx8
> screw and a lock   washer. The finished stack will be link, ring terminal,
>    lock washer. (The fusible link, itself, can be   easily dropped into
> position under the ring terminals
>    after all the wires are in place.)
> 11.Make up a 10 AWG connecting wire with a #10 ring   terminal at one end
> and a 1/4" ring at the other.
>    You should test fit this in the car. In my case,   11 1/2" from ring
> center to ring center allowed a
>    nice neat loop from a rear fuse box screw terminal   to the fan motor
> along side the ABS unit harness,
>    including routing through the aforementioned plastic   wiring clip.
> Again, plan ahead as needed for shrink
>    tubing.
> 12.Route the new wire from the rear fuse box terminal,   which opposes,
> front-to-rear, the one you've used for
>    the original fan motor ground wire, forward along the   ABS unit
> through the wire clip and down to
>    the fan motor's ground terminal.
> 13.Drop the 80A fusible link into place under the ring   terminals, snug
> down the screws, coat the connections
>    with battery terminal sealant or similar and snap the box   cover shut.
> (The box is not weather tight but is well
>    located considering it's under the hood. A little anti-corrosion
> protection would be a good idea.)
> 14.Finalize the wiring dress and snap the wire clip   into the bracket
> Use a cable tie or 2 if you
>    like. I found this not particularly necessary due to   the existing
> the short run and the stiffness of
>    the 10 AWG wire.
> 15.Step back and admire your official factory upgrade.
> 16.Sleep at night.
> Have fun and best luck,
> DeWitt Harrison
> ------------------
> The # of the thermal fuse we use isCB-50 (it is a Borg Warner #)
> Should be available from any good parts house.....
> Later
> Aidan
> www.geocities.com/motorcity/downs/6185
> ------------------
> Below is another way to install a fusible link to protect your cooling
> fanmotor.
> Here is the information regarding the fuse, I picked mine up at Kragen
> autoparts:
> It is made by "Buss Fuses" (Japanese made fuse)
> It is BP/FLB 70 (70 Amp) or you can get BP/FLB80 (80 Amp)
> Install procedure:
> Disconnect ground wire (brown) at fan motor (10mm nut)
> Connect fuse to fan motor post using above nut
> Connect ground wire to the fuse using a 10mm short bolt and a nut
> Make sure you buy two fuses (for replacement purpose)
> You are done, isn't that peachy?
> Regards,
> Avi
> ------------------
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