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Thread: How to test a Viscous Fan Coupling - V8

  1. #11
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    Quote Originally Posted by PhilipA View Post

    The fan will turn forever as long as you keep pushing it. However it should stop immediately you stop pushing, and be a little gluggy like pushing your hand through custard.
    I know it’s an old topic, but...
    Having read as much as I can find on checking the fan including in TGO, I’m still not sure if mine is good or not.
    With the motor off since last night and still not running, I can turn the fan quite easily by hand but it does not free spin. Although it makes a bit of a noise at start up, it isn’t what I would call a roar.
    Does this description sound like it could be a good viscous fan?
    I would like to buy a new one just to be sure but I’m not game, having just splashed out for a new secondhand motor and steering pump.
    2002 D2 4.6L V8 Auto SLS+2" ACE CDL Truetrac(F) Nanocom(V8 only)

  2. #12
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    A good one will roar loud enough to drown out the burble of a V8!
    So as already said, when stone cold, it should be the most obvious thing you can hear, bonnet up or down.
    Then in about 30-60sec, as it starts to decouple itself, you will hear the sound of the motor over the sound of the fan.
    Note tho, a few sec after start up, you do need a few revs(1000-1500 ish) to hear the roar of the fan.
    The more you rev, the louder the fan will be.
    But once it's decoupled itself, you can't hardly hear it over the motor.

    So the easiest test is. From stone cold, start motor, wait about 5-10sec for oil to fully pressurise and circulate, then give it some revs.
    If you can't hear the roar of the fan over the motor noise, most likely it's not working ideally(or at all).
    Could be partially working tho, but a brand new one is very obvious.
    Also, in those first 30-60secs, with bonnet up and a few revs, tweaking by hand the throttle cable obviously from the driver side of the front of the car, you will feel massive amounts of air being forced backward of the fan.
    Then once it's settled and decouples itself, the difference in air from the fan is very obvious.
    Arthur.

    '99 D1 300Tdi Auto
    '03 D2 Td5 Auto

  3. #13
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    They are a diffferent unit to the tdi ones arnt they?

  4. #14
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    Quote Originally Posted by edddo View Post
    They are a diffferent unit to the tdi ones arnt they?
    Not sure on the D1 V8 types, but I think different. I think the D1 v8's use different nut size(36mm vs 32mm for the Tdi).
    But the OP's D2 V8 is completely different, bothy fan and hub.
    Hub nut is 36mm on the V8, fan is much larger, and pulls a ton more air than the Tdi does.
    Fewer blades, but larger and deeper pitch angle.
    I reckon the D2 v8 fan is near enough to one of the strongest fans(other than dads old Cadillac fan) I've had experience with.
    Tdi is barely a puff by comparison.
    Other major difference between D2 V8 fan and Tdi is the direction of removal and fitment(of the threads) .. always catches me out.
    Arthur.

    '99 D1 300Tdi Auto
    '03 D2 Td5 Auto

  5. #15
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    Easy way to remember direction is that they UNDO in the same direction the fan spins.
    PaulT

    REMLR 256 / SLOw 4 (P)

    W/Shops/trailers & GS's
    RRs, Disco's, 110s & 109s.

  6. #16
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    Thanks AK, this is exactly the sort of info I was seeking. It seems that mine is not working optimally. As soon as the cold weather and the wife’s memory fades, I’ll whack a new one in.
    2002 D2 4.6L V8 Auto SLS+2" ACE CDL Truetrac(F) Nanocom(V8 only)

  7. #17
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    Quote Originally Posted by AK83 View Post
    Not sure on the D1 V8 types, but I think different. I think the D1 v8's use different nut size(36mm vs 32mm for the Tdi).
    But the OP's D2 V8 is completely different, bothy fan and hub.
    Hub nut is 36mm on the V8, fan is much larger, and pulls a ton more air than the Tdi does.
    Fewer blades, but larger and deeper pitch angle.
    I reckon the D2 v8 fan is near enough to one of the strongest fans(other than dads old Cadillac fan) I've had experience with.
    Tdi is barely a puff by comparison.
    Other major difference between D2 V8 fan and Tdi is the direction of removal and fitment(of the threads) .. always catches me out.
    Much easier to tell if the V8 variety is stuffed or not by the sounds of it.

  8. #18
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    Quote Originally Posted by AK83 View Post
    A good one will roar loud enough to drown out the burble of a V8!
    So as already said, when stone cold, it should be the most obvious thing you can hear, bonnet up or down.
    Then in about 30-60sec, as it starts to decouple itself, you will hear the sound of the motor over the sound of the fan.
    Note tho, a few sec after start up, you do need a few revs(1000-1500 ish) to hear the roar of the fan.
    The more you rev, the louder the fan will be.
    But once it's decoupled itself, you can't hardly hear it over the motor.

    So the easiest test is. From stone cold, start motor, wait about 5-10sec for oil to fully pressurise and circulate, then give it some revs.
    If you can't hear the roar of the fan over the motor noise, most likely it's not working ideally(or at all).
    Could be partially working tho, but a brand new one is very obvious.
    Also, in those first 30-60secs, with bonnet up and a few revs, tweaking by hand the throttle cable obviously from the driver side of the front of the car, you will feel massive amounts of air being forced backward of the fan.
    Then once it's settled and decouples itself, the difference in air from the fan is very obvious.
    An old thread, but I thought it might be helpful to comment on the importance of this post.

    Having just replaced my viscous fan, for the first time in 10 years of ownership, this is the first time I have ever heard the roar that the fan should make when working properly.

    That means for 10 years I have been running a non working fan.
    Looking back, I believe this is a major reason for the early demise of my original block. IE, running it with less than optimal cooling capacity especially at low speed and high load.

    As most of us are aware, the temperature gauge is virtually useless, so it’s likely that I have had extended periods off-road where the temperature was high, but never high enough to bother the gauge or lose coolant. This, over time, took its toll.

    Now with my new (4.6L How to test a Viscous Fan Coupling - V8) motor I intend to always use my Nanocom to keep a close eye on temperatures.

    In conclusion, if you don’t hear the roar, replace the viscous coupling.
    2002 D2 4.6L V8 Auto SLS+2" ACE CDL Truetrac(F) Nanocom(V8 only)

  9. #19
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    I replaced mine on a previously owned 4.6 p38 made no difference. Until I had the radiator flushed which was a third blocked. After that overheating fixed and also intrduced the roar of the viscous fan . My guess is if your radiator is blocked it wont allow enough hot air through to engage the viscous fan . I assume you serviced your radiator with a engine rebuild.

  10. #20
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    Radiator was replaced a couple of years before due to a small leak, but no blockages. New coupling went in last weekend. As I tried to describe above, I don’t know how hot my old motor was getting, but I suspect there were periods of prolonged high temps, without any outward signs, all due to a faulty fan.
    2002 D2 4.6L V8 Auto SLS+2" ACE CDL Truetrac(F) Nanocom(V8 only)

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