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Old 07-04-2005, 10:03   #1 (permalink)
Jon
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200Tdi - Viscous Fan / Overheating Question

Hi all,

Sorry its a long post - please bear with me...

Vehicle: Defender 200Tdi

I have recently sent my 8 month old viscous fan unit back under
warrenty as I believed it was not functioning correctly. The fan was
much harder to turn when the engine was cold (i.e. first thing on a
morning) than it was after the engine had been running for a while.

On Saturday I received a new replacement unit. I put it on and got
the vehicle upto operating temperature (again reading hot on the
gauge). I then switched off the engine and tried to turn the fan.

With 1 finger I could make the fan spin quite freely. Given that the
engine is supposedly HOT (thermostat had definately opened and all
water hoses where hot to touch) I thought that there should be
significant resistance when spinning the fan????

In short this viscous unit is acting like the last 2 I have had so I
surely this must be an OK unit.

At what temperature do these things begin to show signs or resistance?


This whole issue has come about because the gauge reads about 1 needle
width off the end of the white on the gauge at 60-70mph - But never
goes into the red, even at 80mph, and it never boils.

I have had a new (re-cored) rad, new thermostat and new viscous fan.
I dont believe the head gasket has failed either (no visible signs in
oil or water or at the exhause).

I am fairly sure that all my earths are OK and the gauge does not act
in any strange way as you might associate with bad earths. However,
just to make sure I am going to wire the sender unit and guage direct
to the battery and see if that makes a difference.

Fail in that, are the sender units and or gauges prone to break down?
Does anyone know the part number and cost for a replacement
temperature sender unit??


Anti-freeze is at about 35% - 40% water mix.


Looking for some advice / pointers please...

Thanks
Jon

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Old 07-04-2005, 10:03   #2 (permalink)
Paul S. Brown
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Re: 200Tdi - Viscous Fan / Overheating Question

Jon wrote:

> Hi all,
>
> Sorry its a long post - please bear with me...
>
> Vehicle: Defender 200Tdi
>
> I have recently sent my 8 month old viscous fan unit back under
> warrenty as I believed it was not functioning correctly. The fan was
> much harder to turn when the engine was cold (i.e. first thing on a
> morning) than it was after the engine had been running for a while.
>
> On Saturday I received a new replacement unit. I put it on and got
> the vehicle upto operating temperature (again reading hot on the
> gauge). I then switched off the engine and tried to turn the fan.
>
> With 1 finger I could make the fan spin quite freely. Given that the
> engine is supposedly HOT (thermostat had definately opened and all
> water hoses where hot to touch) I thought that there should be
> significant resistance when spinning the fan????
>
> In short this viscous unit is acting like the last 2 I have had so I
> surely this must be an OK unit.
>
> At what temperature do these things begin to show signs or resistance?
>
>


Umm - If I'm thinking of the right thing, there's no temperature
relationship, merely engine speed - the faster the engine turns the faster
the fan goes, just not at a 1:1 rate.

The viscous coupling is sort of like the torque convertor in an automatic
gearbox - the faster one side of it moves, the faster the other side moves
with the actual movement relying on the oil between to carry it.

P.
--
1992 200 TDI Disco - heavily modified
1982 V8 Range Rover - heavily corroded
2000 Rover 75 - heavily driven
1993 Lexus LS400 - just plain heavy on fuel
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Old 07-04-2005, 10:03   #3 (permalink)
Jon
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Re: 200Tdi - Viscous Fan / Overheating Question


>>

>
>Umm - If I'm thinking of the right thing, there's no temperature
>relationship, merely engine speed - the faster the engine turns the faster
>the fan goes, just not at a 1:1 rate.
>

Well, you learn something every day. I had always thought it was
temperature related.

>The viscous coupling is sort of like the torque convertor in an automatic
>gearbox - the faster one side of it moves, the faster the other side moves
>with the actual movement relying on the oil between to carry it.
>
>P.


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Old 07-04-2005, 10:03   #4 (permalink)
Austin Shackles
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Re: 200Tdi - Viscous Fan / Overheating Question

On or around Mon, 4 Jul 2005 11:32:16 +0000 (UTC), Jon <nospam@nospam.com>
enlightened us thusly:

>At what temperature do these things begin to show signs or resistance?


fecking hot. Basically, it's only going to spin up under severe
provocation. They all start off stiff when cold, they should then go free
or nearly-free once run for about 30 seconds or so at moderate engine
speeds. At 80 mph, it's unlikely to 'cos there's lots of airflow anyway.

The only time I've had one spin up again in earnest was when tuning an LPG
system, running at 3000 rpm for several minutes with the vehicle stationary.

>This whole issue has come about because the gauge reads about 1 needle
>width off the end of the white on the gauge at 60-70mph - But never
>goes into the red, even at 80mph, and it never boils.
>
>I have had a new (re-cored) rad, new thermostat and new viscous fan.
>I dont believe the head gasket has failed either (no visible signs in
>oil or water or at the exhause).


replace the sender unit on the engine.

--
Austin Shackles. www.ddol-las.fsnet.co.uk my opinions are just that
"Quos deus vult perdere, prius dementat" Euripedes, quoted in
Boswell's "Johnson".
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Old 07-04-2005, 10:03   #5 (permalink)
Tim Hobbs
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Re: 200Tdi - Viscous Fan / Overheating Question


>Umm - If I'm thinking of the right thing, there's no temperature
>relationship, merely engine speed - the faster the engine turns the faster
>the fan goes, just not at a 1:1 rate.
>
>The viscous coupling is sort of like the torque convertor in an automatic
>gearbox - the faster one side of it moves, the faster the other side moves
>with the actual movement relying on the oil between to carry it.
>
>P.


That can't be right Paul - you'd never get any cooling when idling
which is precisely when you need it most (when no air is flowing over
the rad due to vehicle speed).

Pretty sure it's temp related....


--

Tim Hobbs

'58 Series 2 88" aka "Stig"
'77 101FC Ambulance aka "Burrt"
'03 Volvo V70
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Old 07-04-2005, 14:02   #6 (permalink)
Badger
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Re: 200Tdi - Viscous Fan / Overheating Question


"Jon" <nospam@nospam.com> wrote in message
news:bfaic1hvc1lo8msi6iakegk1n7ctignav7@4ax.com...
>
>>>

>>
>>Umm - If I'm thinking of the right thing, there's no temperature
>>relationship, merely engine speed - the faster the engine turns the faster
>>the fan goes, just not at a 1:1 rate.
>>

> Well, you learn something every day. I had always thought it was
> temperature related.


It is!

>
>>The viscous coupling is sort of like the torque convertor in an automatic
>>gearbox - the faster one side of it moves, the faster the other side moves
>>with the actual movement relying on the oil between to carry it.


Sort of correct, except the oil is a silicon based fluid that is only
allowed to flow into the drive chamber under centrifugal force of the
rotating hub, as the bi-metallic spring opens the valve ports.
The viscous fan is often blamed for temp related issues, when there is in
fact nothing wrong with it. It is an extremely reliable piece of kit that
rarely goes wrong. I'd look at your temp indication system first, my initial
port of call would be the sender unit.
Badger.


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Old 07-05-2005, 17:02   #7 (permalink)
Jon
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Posts: n/a
Re: 200Tdi - Viscous Fan / Overheating Question - Update & more questions

Sorry, another longish post but help and advice is needed!

Thought Id check out my electrics tonight before replacing the sender
unit.

When sender unit is unplugged and wire shorted to earth, guage shoots
over to beyond the red (as it should).

Does anyone know what voltage I should have at the Water Temperature
Sender Unit?? 12V or 5V??? I have 5V, give or take a bit...

12V gets fed into the temperature gauge and 5V comes out and goes to
the sender unit.

However, I have 2 black wires (apparently to earth) connected together
in 1 bango type connector which is attached to the holding / fixing
screw on the back of the temp gauge. If I remove this I get 12V out
of the temp gauge and 12V to the sender unit.

When 12V goes through the sender unit the gauge reads (with a cool
engine) somewhere in the red - clearly incorrect.

I have checked the Haynes manual and cant see any mention of these
black wires connected to the gauge - Are they supposed to be there?
Coincidently there is the same arrangement to the rear of the fuel
gauge?

I have also removed the gauge to check continuity through the +12V to
the holding screw and there is a path through - Is this correct as I
was expecting the screw to be isolated from the gauge body.

Thanks again for advice & pointers.
Jon



On Mon, 04 Jul 2005 13:58:15 +0100, Austin Shackles
<austinNOSPAM@ddol-las.net> wrote:

>On or around Mon, 4 Jul 2005 11:32:16 +0000 (UTC), Jon <nospam@nospam.com>
>enlightened us thusly:
>
>>At what temperature do these things begin to show signs or resistance?

>
>fecking hot. Basically, it's only going to spin up under severe
>provocation. They all start off stiff when cold, they should then go free
>or nearly-free once run for about 30 seconds or so at moderate engine
>speeds. At 80 mph, it's unlikely to 'cos there's lots of airflow anyway.
>
>The only time I've had one spin up again in earnest was when tuning an LPG
>system, running at 3000 rpm for several minutes with the vehicle stationary.
>
>>This whole issue has come about because the gauge reads about 1 needle
>>width off the end of the white on the gauge at 60-70mph - But never
>>goes into the red, even at 80mph, and it never boils.
>>
>>I have had a new (re-cored) rad, new thermostat and new viscous fan.
>>I dont believe the head gasket has failed either (no visible signs in
>>oil or water or at the exhause).

>
>replace the sender unit on the engine.


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Old 07-05-2005, 17:02   #8 (permalink)
Austin Shackles
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Posts: n/a
Re: 200Tdi - Viscous Fan / Overheating Question - Update & more questions

On or around Tue, 5 Jul 2005 20:38:49 +0000 (UTC), Jon
<jonathan.kelly@nospam.lstc.co.uk> enlightened us thusly:

>12V gets fed into the temperature gauge and 5V comes out and goes to
>the sender unit.
>


mostly, the temperature gauge is an ammeter. Basically, the resistance of
the sender changes with temperature, resulting in more or less current
flowing. There are 2 ways of doing it: more current = more deflection is
common, as proved by the thing going to the top of the dial when you earth
the other end.

The sender can get senile in various ways.

interestingly, the somewhat out of date intermotor book I have here doesn't
list the temp sender for the TDi engines. Which is a pity, 'cos if it did,
I could've got the specs for it for you.

--
Austin Shackles. www.ddol-las.fsnet.co.uk my opinions are just that
"Quos deus vult perdere, prius dementat" Euripedes, quoted in
Boswell's "Johnson".
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Old 07-05-2005, 17:02   #9 (permalink)
Graham Wilkinson
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Posts: n/a
Re: 200Tdi - Viscous Fan / Overheating Question


Evening guys

I too would be very interested in this info as my 200tdi defender is
doing the exact same thing and is also on its 3rd viscous unit!! I have
also changed the head gasket, water pump, thermostat, sender and rad and
am now stuck.
I would of thought that when the engine is cold the fan should spin
slowly increasing to engine speed when the engine is hot and the hot
air that passes through the rad. But you can stop mine easily when
warm!!
Graham


--
Graham Wilkinson
------------------------------------------------------------------------
Graham Wilkinson's Profile: http://www.landyzone.co.uk/lz/member.php?userid=195
View this thread: http://www.landyzone.co.uk/lz/showthread.php?t=23762

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Old 07-06-2005, 01:02   #10 (permalink)
Jon
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Re: 200Tdi - Viscous Fan / Overheating Question - Update & more questions

Austin,
Thanks for looking in the book. Have you any ideas if those curious 2
black wires (earths?) should be connected to the fixing screw at the
rear of the gauge?



I wonder if someone could possibly measure the voltage between the
sender unit and its supply lead as this would appear to be key. I am
guessing it should be 12V (not 5V like mine) and thus the sender is
stuffed, however, if it should be 5V the quest still remains!


Graham:
Out of interest, as your gauge is reading incorrect, what voltage have
you got at the sender unit?

Thanks
Jon

On Tue, 05 Jul 2005 22:57:10 +0100, Austin Shackles
<austinNOSPAM@ddol-las.net> wrote:

>On or around Tue, 5 Jul 2005 20:38:49 +0000 (UTC), Jon
><jonathan.kelly@nospam.lstc.co.uk> enlightened us thusly:
>
>>12V gets fed into the temperature gauge and 5V comes out and goes to
>>the sender unit.
>>

>
>mostly, the temperature gauge is an ammeter. Basically, the resistance of
>the sender changes with temperature, resulting in more or less current
>flowing. There are 2 ways of doing it: more current = more deflection is
>common, as proved by the thing going to the top of the dial when you earth
>the other end.
>
>The sender can get senile in various ways.
>
>interestingly, the somewhat out of date intermotor book I have here doesn't
>list the temp sender for the TDi engines. Which is a pity, 'cos if it did,
>I could've got the specs for it for you.


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