Engine fan viscous unit......

[Towpack]

Anyone had any dealings with repair of the viscous fan drive unit? Mine seems to be stuck in the driven position, not fully locked but quite stiff to turn hot or cold. Within a minute or so of a cold start it should be fully unlocked and, ‘freewheeling’, in effect until the engine gets hot enough to operate the unit. This is how it used to be and only ever seemed to come into play when towing in Summer. The fan makes quite a roar when it’s engaged which is how I noticed it.

 

[Grimbo]

Hi ,
Some people reckon you can refill or change the silicone grease inside them , personally I would just fit a new OE one as it's not something you want to fail just when you need it or even fail and put the fan into the Rad .....something I've seen on AG and Plant . More common is to fail so the fan isn't driving enough , I have known them fail to the extent that you could stop the fan with a piece of wood even at high engine RPM

 

[Brett]

Roughtrax do the OE Aisin fan blades & Viscous clutches.

Just replaced my fan blade after breaking it. Aisin from RT was spot on.

 

[Towpack]

Drive failure is usually caused by fluid loss. As my problem is the opposite I’m guessing the bi-metallic strip operated valve is stuck open allowing the fluid through to the viscous plates irrespective of temperature?
+1 on the new replacement being a preferred option and the Aisin unit from RT is way cheaper than OEM even via Amayama.

 

[Brett]

Sorry Towpack, you are correct, it is Aisin, not Denso. Senior moment.

 

[grantw]

Mine failed the same way - new one from RT and unsurprisingly good as new.

 

[frank rabbets]

The centre/front gets corroded and seized. I packed plenty of grease in mine to prolong it's life. Not much centrifugal force in the centre so grease still there.

 

[Towpack]

I think Ill just go ahead and order the new unit from RT. I was intending to get the old one off for inspection and testing but removing it isn’t as quick as I expected. The fan isn’t coming out without the fan shroud which also means both batteries and battery trays coming out so might as well do it once and fit the new one.

 

[Towpack]

New Aisin unit fitted and working perfect again. It was obvious immediately by the lack of fan noise. The roar when the fan is “working” is quite marked. No danger of overheating with a permanently locked fan of course so I guess all I’ve gained is a quieter engine and a theoretical (minuscule) increase in power and MPG but every little helps!

 

[Bert]

New Aisin unit fitted and working perfect again. It was obvious immediately by the lack of fan noise. The roar when the fan is “working” is quite marked. No danger of overheating with a permanently locked fan of course so I guess all I’ve gained is a quieter engine and a theoretical (minuscule) increase in power and MPG but every little helps!

Hello Towpack
How has the unit faired since you installed it?
My viscous fan requires attention and I'm at the same crossroads that you were at, repair or replace?
Cheers

 

[Towpack]

Still working perfectly. I don’t know for sure if the one I replaced was the original from new but I reckon 10-15 years and 100k+ miles is a reasonable life expectancy. Out of curiosity I stripped the old unit and it still had plenty of oil in there which I expected to be honest as it had no external leaks so it was obviously some other problem preventing correct operation.

 

[Bert]

Still working perfectly...... Out of curiosity I stripped the old unit and it still had plenty of oil in there which I expected to be honest as it had no external leaks so it was obviously some other problem preventing correct operation.

Interesting about the original viscous unit still containing fluid.... I think I'll buy a new ASIN unit too. Then take the old one apart and see what the condition is. Cheers.

 

[PeterLC]

Is this to say that if I hear my fan engaging and roaring every so many minutes while driving on the highway in warm weather, it is actually starting to fail the way Towpack's did ? I've never seen the engine temperature go up before it engages and can't see it go down after it engaged.

 

[Towpack]

I don’t believe the OEM temp gauge is that sensitive. Mine held the same position when just warmed up as it did towing a caravan in 30 deg heat on the motorway when the viscous fan was fully engaged (and obviously doing a good job) but I’ve no idea what the temp range was. I think it’s Dave2000 on here who has done a gauge mod that makes it much more reactive to temp changes and hence more useful.

 

[PeterLC]

My temp gauge is already modified to Dave2000 instructions. But I didn't expect the fan to run and roar on a motorway at 110km/h & 20°C,not towing anything. Do you have that behaviour from the new Aisin coupling ? I'm also considering a swap, just don't know what to expect.

 

[Grimbo]

Just changed the unit on my 150K miles 24 valve engine .
The original unit was running the fan all the time despite being able to turn the fan easily with the engine off .
The new OE unit felt little different when spinning it by hand before fitting ....... so much so I have not fitted it for several moths thinking I had better things to do .
Difference is night and day ..... with the new one fitted the fan runs at full speed for a few seconds on start but then just idles ...... much quieter drive now without the fan engaged all the time and will no doubt see an improvement in MPG .....it seems a bit more sprightly too .
If asked I would have said the original was fine .....
Having tested a fair few tractors on a dyno it's not uncommon to see a big cooling fan take well over 10hp/15hp to drive ....we now as in many vehicles use electronically engaged cooling fan cluches so we can control what the fan is doing both for economy but also a transmision can be running very how while the engine is running cool due to our specific types of use so with all the data on the CAN many parameters can be used to spool the fan up and down as needed .

 

[Andy Daws]

I've just replaced mine with a RT Asin unit too and yes, it makes a huge difference, mine was also driving all the time, now it's a LOT quieter.

 

[PeterLC]

I followed in this row. Diesel use went from 9,6 l/100km to 8,5l/100km (24V engine) (28mpg). And I can listen to the radio again, even on highways.