viscous fan confusion - check?

[andycook]

i have been searching threads about viscous fan operation,
and confused

as far as I can gather,
when engine is cold - and you spin the large rad fan by hand, it should spin freely.
when engine is hot and you jump out and spin the fan, it should be harder to spin

On my 4runner - I checked 1st thing this morning, cold engine, the fan spun, but not that easily.
On the way to work, driving at 60-65 mph on dual carriageway,
I stopped at top of a hill, and spun the fan - it spun Very very easily and rotated a few times after a flick. it spun a lot more easily than when engine cold.

so my fan seems to work opposite to what I believe
although - with oil inthe fan clutch, i would expect that to get less viscous with heat,

maybe this explains the recent overheating problem i had on a long hill?
can anyone clarify this?

thanks

[stara]

your viscous fan is indeed doing the opposite to what it should, it should be v stiff if not solid when the engine is hot,

i think this is the main reason that we see a lot of head failures, due to overheating caused by dodgy fans.

replace fluid, or replace fan, or fill with glue and have a permanent fan.

oh, and silicon fluid solidifies as it gets hotter.

[andycook]

many thanks

thats cleared that up - and explained the overheating I had

another thing to fix.... it seems to be never ending, but the vehicle has done 140k miles, but I still enjoy driving it!

[NiftyNev]

andycook

Engine cold - Fan should be fairly hard to turn.If you give it a flick it should only turn one or two blades.This is because the fluid is cold and has a higher viscosity.

Engine warm - Fan will be easier to turn.Give it a flick and it should spin more freely.The amount of turn can vary quite a bit depending on temperature and from vehicle to vehicle.This is because the fluid is getting hotter and has a lower viscosity.

Engine hot.The fan will still spin a small amount if temperature is not high enough for the heat of the fluid to act on the metal spring which is also in the clutch mechanism of the fan.As this is heated it causes the fan to lock and therefore spin at engine speed to aid cooling.

The engine temperature at idle is usually not high enough to lock the fan and therefore you can't determine if the fan is operating correctly this way.Mine rarely locks and when it does it is usually under load and I can hear it from inside the vehicle.When this happens it is only operating at full speed for a few seconds at a time.The fluid inside the fan gets thinner as it heats up and certainly does not solidify.

Hope this info helps.

Neville

[stara]

andycook

Engine cold - Fan should be fairly hard to turn.If you give it a flick it should only turn one or two blades.This is because the fluid is cold and has a higher viscosity.

Engine warm - Fan will be easier to turn.Give it a flick and it should spin more freely.The amount of turn can vary quite a bit depending on temperature and from vehicle to vehicle.This is because the fluid is getting hotter and has a lower viscosity.

Engine hot.The fan will still spin a small amount if temperature is not high enough for the heat of the fluid to act on the metal spring which is also in the clutch mechanism of the fan.As this is heated it causes the fan to lock and therefore spin at engine speed to aid cooling.

The engine temperature at idle is usually not high enough to lock the fan and therefore you can't determine if the fan is operating correctly this way.Mine rarely locks and when it does it is usually under load and I can hear it from inside the vehicle.When this happens it is only operating at full speed for a few seconds at a time.The fluid inside the fan gets thinner as it heats up and certainly does not solidify.

Hope this info helps.

Neville

nev, you seem to be confusing silicon fluid with ordinary oil, silicon fluid (the formula that is used in viscous couplings) solidifies (gels) as it gets hot. and acts in the opposite way to a mineral or synthetic lubricating oil.

now for the science bit


Thermal degradation at elevated temperatures causes rearrangement of the silicone-oxygen bonds to produce volatile by-products. Free-radical reaction of the methyl groups to form cross-linked materials by oxidation with peroxy compounds increases fluid viscosity and causes the fluid to gel.

[andycook]

see what I mean - different opinions!

This is why I got confused reading past threads...

As Nev now says the opposite to everyone elses advice on how the fan coupling works.....

e.g. hard to turn fan when cold...

the fan on our 4runner has one of those coiled springs at the front ?
Do all Surf and 4runners have the same system?

[NiftyNev]

nev, you seem to be confusing silicon fluid with ordinary oil, silicon fluid (the formula that is used in viscous couplings) solidifies (gels) as it gets hot. and acts in the opposite way to a mineral or synthetic lubricating oil.

now for the science bit


Thermal degradation at elevated temperatures causes rearrangement of the silicone-oxygen bonds to produce volatile by-products. Free-radical reaction of the methyl groups to form cross-linked materials by oxidation with peroxy compounds increases fluid viscosity and causes the fluid to gel.

Are you sure that the above applies to the fluid in viscous fans?The explanation I have given regarding the operation of the fan is based on the way mine operates and info from many other sources.If in fact the fluid does gell then after engine reaches operating temperature the fan would be operating at engine speed continuously.This does not happen.If airflow through radiator is sufficient the fan is not needed.Maybe I am wrong but I know what my fan does amd my cooling system works perfectly.

Neville

[Koi]

Are you sure that the above applies to the fluid in viscous fans?The explanation I have given regarding the operation of the fan is based on the way mine operates and info from many other sources.If in fact the fluid does gell then after engine reaches operating temperature the fan would be operating at engine speed continuously.This does not happen.If airflow through radiator is sufficient the fan is not needed.Maybe I am wrong but I know what my fan does amd my cooling system works perfectly.

Neville

Wow confucious say:
I thought that the fan turned slowly at low temp due to the thin viscosity of the oil and as the temp goes up the viscosity of the oil thickens causing the fan to be turning all the time as more air flow is theoritically needed.
Now think about this, if the fan is driven all the time under hot temp conditions then it saps a bit of power and mpg albeit fractional.
So a common upgrade is to fit electrical fans (kenlowe) so they don't sap the power like viscous fans do.
If they run like yours does or don't under hot temp then there is no need to do the conversion to electric fans!!!!!!!!!!!!
Also as I recall a way to check if a fan is running correctly is that when engine is cold and switched off you should be able to turn the fan reasonably easily with a little resistance. Now start it up and with a rolled up newspaper shove it in the fan and you should be able to stop the fan. Now allow the engine to get hot and shve the newspaper in it again, mind your hands as the newspaper as it will be shreded apart.

[andycook]

confusion continues

tried the newspaper trick

engine cold - newspaper didnt stop fan and shredded edge
engine hot - newspaper STOPPED the fan!

do all the viscous fans on all models have that coiled metal widget on exterior nearest the rad ?

confusion continues...

[stara]

ok maybe some confusion here,

first point, silicon fluid does NOT get thinner when heated, it gets thicker

it is not the just fact that the fluid 'solidifies' that locks the fan, as temp variations wouldn't allow it to work efficiently in this manner

the fan locks due to a bimetallic strip (a spring looking thing) openeing 'channels' to allow the fluid to travel to the outer edges of the fan housing causing the fan to lock.

all viscous fans work this way albeit with slightly different designs

all viscous fans use silicon fluid as regular oil would get thinner as the engine got hotter

if your fan is locked up when cold, it is broken, if your fan is spinning freely when hot, it is broken.

[TonyN]

Don't get to involved in the details, warm the car up, switch off engine, then spin the fan by hand.

You should feel some drag, and it won't turn more than 1/4 of a turn after you let go after spinning it hard.

If it freewheels, you won't be getting any drive when running and therefore won't pull much air through.

If its locked up, your wasting fuel by solidly driving it all the time and you hear the woooshing noise all the time.

The details.......

You only need the fan at low speeds and tick over, anything about 40mph and windspeed is enough to keep the rad cool, which is why you have a viscous coupling, to stop the fan doing 3000+ revs when you on the motorway and making your MPG even worse.

There is an bi-metallic strip in the coupling, thats lets the fan slip/drive more according to the air temp reaching the coupling through the radiator (ie, if the air reaching the coupling is to for the revs the fan is doing, say if its really hot weather or the engine is working hard, if will allow less slipping for the given RPM.

The strip is adjustable, you can fool the coupling into thinking its to hot, and drive harder than factory settings, but will cost you on the fuel/power stakes as its turning the fan at a high RPM.

And no, I don't know which way to adjust it.

A little reaserch shows that Japans average annual temps range from 6-22 degC, and the UK is 8-11 degC. So in my humble opinion, Japan spec fluid couplings are fine for UK climate, I would'nt bother messing with it.

Enjoy.........



Job done!

[andycook]

thanks

so..... do you reckon the fan is broken because of dodgy fluid?
or dodgy bimetalic coil thingy? (which doesn't look snapped)

andy

[rich]

According to Autorepair:

Rear wheel drive cars with longitudinal engines usually have cooling fans driven by the engine. The fan is not always needed and it takes horsepower from the engine to turn. These fans have a thermostatically controlled viscous fan clutch. As the fluid in the fan clutch gets hot, it gets thicker making the fan turn faster. The fan clutch is located in the air stream and reacts to the temperature of the air. It also helps the engine reach operating temperature by not engaging until it's needed.



And for the technically minded.

Viscous Coupling

A device that resists differences in rotational speeds. Technically, it is a small sealed drum filled with a measured amount of silicon fluid. Also inside the drum are two sets of interleaved plates; one set of plates is attached to the outer drum, and one set is attached to the inner shaft. As long as both the drum and the shaft, and therefore both sets of plates, turn at the same speed, there will be no relative motion between the plates. However, where one of the two turns faster than the other, the plates develop relative motion and begin slicing through the silicon liquid. This causes it to heat and solidify, causing the plates to lock together. With the plates locked, relative motion stops. The silicon then cools and returns to a liquid state, releasing the plates.

And if you then say "Well why does it roar from cold" after sitting awhile the oil in the viscous clutch tends to settle. At start up it redistributes and while it does, the fan runs.


Rich.

[TonyN]

thanks

so..... do you reckon the fan is broken because of dodgy fluid?
or dodgy bimetalic coil thingy? (which doesn't look snapped)

andy

Yeah, you've probebly run out of fluid, you can get little tubes of it from Toyota, the part No is one the forum somewhere.

[rich]

The Toyota part no. is. 08816-03001 oil silicone. You need 2 tubes apparently.

http://www.yotasurf-online.co.uk/pub...t=silicone+oil