viscous fan

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smithyzen

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Hi everyone, new to this but here goes,
I have a 2003 2.9 diesel vogue, I fitted a genuine Land Rover tow bar to it with the dedicated vehicle specific wiring kit, towed the caravan home for the first time (with the Range) no problem, all lights worked etc, Today going to work (not towing) I notice that the cooling fan was running or engaged all the time, quite noisey, it stayed engaged all the time although the temp gauge stayed normal. Is this a coincidence, has the fan seized up or what, does the wiring kit have anything to do with the running of the fan? is Fan failure common ?
 
smithyzen said:
Hi everyone, new to this but here goes,
I have a 2003 2.9 diesel vogue, I fitted a genuine Land Rover tow bar to it with the dedicated vehicle specific wiring kit, towed the caravan home for the first time (with the Range) no problem, all lights worked etc, Today going to work (not towing) I notice that the cooling fan was running or engaged all the time, quite noisey, it stayed engaged all the time although the temp gauge stayed normal. Is this a coincidence, has the fan seized up or what, does the wiring kit have anything to do with the running of the fan? is Fan failure common ?
Click to expand...

The viscous fans do run all the time, just a bit less when cold, when its cold feel it there should be a bit of a resistance, if it's solid then its fooked, also make sure there is no play in the bearings.

I threw mine away and fitted an electric fan, rarely comes on, only after a run when stopped, or off roading.
 
Hello Smithy,

Normally the viscous fan coupling turns at low speed induced by relatively low coupling forces between the housings. These extracts from my essay on them explains how and why they fail:

"Viscous Fan Coupling (Clutch Fan) uses the unique properties of a silicone oil whose viscosity changes both with sheer force and temperature. A grooved wheel (fixed to the water pump) rotates within a grooved housing (fixed to fan blades) and the oil is forced to move within and between the revolving grooves.

Normally a bimetal coil senses the airflow coming from the radiator. Heat causes the coil to turn a shaft which operates an internal control valve regulating the volume of oil which is able to flow between the grooves. Thus hotter air allows more fluid to enter the grooves resulting in a stronger bond between wheel and housing giving higher fan speed and increased cooling.

The larger the speed differential between oil layers in the wheel and housing the greater the sheer forces which raise the temperature and viscosity of the oil. The increased bond between the two causes the fan to rotate faster increasing airflow through the radiator. As speed difference falls, sheer forces and oil temperature fall, the oil gets thinner, the driving force lessens and fan speed stabilises."

"The first of two fail conditions is when the fan does not speed up due to insufficient bond between the wheel and the housing resulting in overheating especially in slow traffic, urban driving, towing or running air-con. Lightly loaded at normal driving speed there is sufficient air passing through the radiator to cool the engine. There are three reasons for such failure. Faulty bimetal coil, oil control shaft/valve siezed, or loss of oil. A simple check is to press a rolled newspaper against the fan blades when a hot engine is idling. If the fan can be slowed or stopped it is probably faulty."

"A second fail condition when the fan becomes permanently locked is potentially very serious. Because the grooves are thin they can break due to age, internal corrosion, vibration, etc, with debris jamming between wheel and housing resulting in an over speed fan. The air roars loudly and continously, more so at high engine speeds and such a condition may result in a thrown fan blade, resulting in severe imbalance and further breakage. If this happens broken parts are projected forwards into the radiator. Never drive a car with a locked-up viscous fan."

There is no electrical function on the viscous fan coupling, however, one might speculate that a prolonged towing journey may have caused the viscous unit to work very hard where previously it had an easy life and the extra fluid pumped in by the process has not been automatically released, so it remains locked.

Try rotating the fan blades by hand - engine off, or try slowing them with a rolled newspaper - engine idling, to see if you can unlock the bond.

Hope this helps
 
Thanks Ramon, my situation sounds like the case you highlighted in red, very loud, increases with engine revs, I did not tow my caravan very far, and certainly it did not put much strain on the vehicle,empty van no passengers etc, my own thoughts on this are that in normal everyday use the fan was hardly in use, the first time it had to do any work it locked up, it has definately only happened since I towed my caravan home. I did try moving the fan blades by hand with the engine NOT running and they moved easily, so i am a bit confused at the mo !
 
smithyzen said:
Thanks Ramon, my situation sounds like the case you highlighted in red, very loud, increases with engine revs, I did not tow my caravan very far, and certainly it did not put much strain on the vehicle,empty van no passengers etc, my own thoughts on this are that in normal everyday use the fan was hardly in use, the first time it had to do any work it locked up, it has definately only happened since I towed my caravan home. I did try moving the fan blades by hand with the engine NOT running and they moved easily, so i am a bit confused at the mo !
Click to expand...

Sounds to me it's working fine, if it had siezed up you would feel it cold with the engine off. Next time you think its faulty jump out and rev the engine up from under the bonnet,you should find that the fan lags behind as you rev it, and builds speed up progresively as it catches up with the engine.
 
And to confuse the matter further, when starting from a cold engine it will take a little while for the fluid to sort itself out so initially the fan will feel stiff to turn but should ease off fairly quickly.
 
Not sure whats going on, the fan is definately MUCH MUCH noisier then before I towed, the noise of the fan is making the car undriveable, something is WRONG.
 
Ratae said:
And to confuse the matter further, when starting from a cold engine it will take a little while for the fluid to sort itself out so initially the fan will feel stiff to turn but should ease off fairly quickly.
Click to expand...

I noticed the phenomenom you describe recently and put it down to the same reason - fluid being trapped in the viscous when the car is parked up hot, and taking its time to disperse when next started. - usually less than a couple of minutes though. Also pressing a rolled newspaper against it straight away might help to diagnose if its really toast.
 
Thanks for all the help guys, checked the fan again and it turns but is stiff, I was under the impression that they were quite free spinning when not actually engaged, looks like I will have to get the spanners out, anyone know of a good cheap place to get one?
 
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