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

Reply to
Jon
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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.

Reply to
Paul S. Brown

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

Reply to
Jon

On or around Mon, 4 Jul 2005 11:32:16 +0000 (UTC), Jon enlightened us thusly:

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.

replace the sender unit on the engine.

Reply to
Austin Shackles

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....

Reply to
Tim Hobbs

It is!

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.

Reply to
Badger

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

Reply to
Jon

On or around Tue, 5 Jul 2005 20:38:49 +0000 (UTC), Jon enlightened us thusly:

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.

Reply to
Austin Shackles

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

Reply to
Graham Wilkinson

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 J>On or around Tue, 5 Jul 2005 20:38:49 +0000 (UTC), Jon

Reply to
Jon

On or around Tue, 5 Jul 2005 22:43:55 +0000, Graham Wilkinson enlightened us thusly:

OK, viscous fans in a nutshell:

(If it's working properly)

Initially on cold start-up: fan spins fast, makes a lot of noise on a V8 one.

After about 30sec or so (more if it's at idle): fan frees off and spins down. You can hear it do that quite clearly on a V8, less so on a TDi thanks to more engine noise and more sound deadening. Try it with the bonnet up - start the engine, run it at about 2000 rpm and watch/listen to the fan, after a bit you should see and hear it slow down.

Normal running - engine at normal temp: fan stays free. Minor overheat such as climbing a big hill in low gear doesn't generally make it hot enough to cut back in.

Engine overheating or working hard and stationary: fan will cut back in and spin up again, but it needs to be pretty hot to achieve this. If it actually boils, without the fan cutting in, then you can reasonably say that it's not working. The times I've seen one cut in were doing silly stuff like tuning the gas system, running at 3000 rpm in the workshop for several minutes. When the fan comes in, it's unmistakable. Quite honestly, I doubt you can provoke a TDi into doing that - they run cold, normally, unless there's an actual fault. I guess you'd only really need the fan in heavy slow towing or other extreme conditions like sustained winching, maybe.

Reply to
Austin Shackles

OK, replaced the sender last night with new (genuine) one.

Exactly the same temperature readings...bugger!

Some nice chap on the LRO Forum also confirmed that the voltage to the sender should be between about 4.5V - fine there then.

That leaves me with 2 options:- 1. Gauge is faulty (doubt that) 2. Engine is actually running hot

I now suspect that my engine is running a bit too hot...Question is what would cause that?

I did notice last night that when hot (never noticed it when cold) I get a bit of air/oil vapour blowing out from under the oil filler cap. I have known for some time that the oil breather that feeds to the air filter puffs oily vapour out, but isnt that what its supposed to do?

What would cause pressure in the rocker box, enough to blow through the filler (a breather blocked somewhere), and would this cause it to run hot??

Thanks Jon

Reply to
Jon

Run the engine with the oil filler cap off - does it "chuff" (sounds a bit like a subdued pop-pop)? Again, run the engine with the dipstick removed (at idle!) - is there a chuffing though there? Finally, is the air filter oily (i.e. more than just a little bit on the lower front end of the filter? If any/all of the above are present, then the head gasket is suspect. If there is only slight evidence of the above then get a compression test done (don't know if you have already done that) - you should be looking for one or two cylinders being a lower than the others - Nos. 3 and 4 are the usual culprits on 200Tdi's.

If the above are all clear, then a cracked head would be the next thing to investigate.

Richard

Reply to
beamendsltd

Richard, Many thanks for this. I will check these things out at the weekend and see what noises I can hear.

As for the compression test - havent done this yet. What should would be an acceptable compression? I know that it is more important to have 4 equal'ish pots but what value would you expect them to be?

Thanks J>>

Reply to
Jon

Centripetal force (or, in fact, lack thereof...)

:-)

Reply to
Tim Hobbs

I didn't want to confuse the issue Tim! People understand centrifugal force, a lot have never even heard of centripetal force. Badger.

Reply to
Badger

Its all a matter of perspective. You can't have one without the other.

Steve

Reply to
steve Taylor

like those little beasties in the garden with all the legs?

Regards. Mark.

Reply to
MVP

Except that there is no such thing as centrifugal force. It doesn't exist.

Reply to
Tim Hobbs

Oh yes it does.

From the perspective of the support around which a mass spins, of course it does. Does the support feel the spinning mass pushing it, or pulling it ? Is your frame of reference fixed or rotating ? If its rotating, as it is in your physical experience with a lump on a rope say, then *you* experience a centrifugal force.

Of course, if the force really was acting through the centre of mass of the object and the centre of rotation, it would fly away radially, and not tangentially, so we know that the action from the rotating masses point of view is towards the centre, since the mass wishes to travel in a straight line in the absence of any external forces.

Steve

Reply to
steve Taylor

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