If the clutch is working well, you will not be able to stop the fan when it is hot. In my case, after driving for 10-15 minutes when it is 100f out, the fan at idle is pushing noticable air and I was unable to slow it down to any noticble degree, even when applying quite a bit of pressure. An easy way to check is to hold a rolled up rag and put that against the fan. If the clutch is bad the fan will instantly slow down to a stop.
How do you test fan viscous coupling??
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e9999 said:
Yes, I don’t have as much of a start up rev (engine RPM) as others have reported the engine finds idle within a second or two, the fan roars for at least 10 seconds, it is 84 right now, engine has been off since last night. IIRC it is longer in cold weather. With the hood open you can easily hear and see the fan slow down after the “whoosh” it is noticeably slower than the input. You can also hear it from the driver’s seat but you may have to be paying attention.
I have never noticed my new one "cycling" on and off , but sitting at a long light ac on in hot weather when it finally turns green you can hear the fan and feel the loss of power for a few seconds until it disengages. My old one never did this. It is subtle you do have to listen for it.
Maybe if I were to start it at idle with the AC on a hot day and let it warm up it would start cycling? Never have done that.
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e9999 said:
- For whatever reason, there is a short (15 sec) whoosh of the fan on start (even on cold start) before the fan slows again, but is still moving
- Agree on the other point that this depends on the heat. I don't think the fan ever 'stops', but the power of the fan does chnage based on the heat experienced by the fan clutch. I believe the newer clutches have 'three speeds' vs two (?)
- As I've posted in other threads, the 'Robbie Test' is no big deal, especially if the clutch is shot (not that I want to test it on one that is working well). After a long drive, I was able to stop my fan and hold it for a number of minutes with just my (leather clad) pinkie. Use a towel if you want.
- Before I chucked my old one, the one thing I noticed is that as I spun the old clutch there was similar resistance and then it became quite easy to turn (sort of felt like when you are backing a nut off, easier to turn as you go). The new clutch maintained the same resistance. That siad, I think it's hard to feel the difference old vs. new - the Robbie Test is a good one and not as unsafe and harmful as it sounds.
- One more point - when y fan was blowing with the old clutch there was a 'strong breeze' when you put your hand (carefully!) aft of the fan. With the new one it is a strong gale!
- I posted in the 'it's hot' thread my instructions on how to replace - very much a one
job. I did mine in my driveway in less than 45 min without any major work. Given that this is a $115 part and it's not a huge install, I think the overall PM value of this is quite high, especially considering the cooling issues associated with this truck. If you think/are concerned that the clutch is shot, replace it.Cheers, Hugh
Last edited:
(this post edited for new numbers)
thanks for the above.
here is my situation:
- no overheating problems noted
- no whoosh on cold start that I could tell, though. That doesn't seem good based on above.
- with engine fairly cold (clutch shaft at 90F), right after engine start I pressed my fingertips (with glove) against the rear of the fan blades. Pressed as hard as I was comfortable doing and the fan did indeed actually stop fairly readily. That seems OK if cold. Tried again when hot (150F at the fan shaft, after 20 mins of idling, upper rad hose at about 155F, air coming out of shroud at 150F or so), I pressed much harder than before and as hard as I was comfortable, and the fan slowed down a bit but I could not stop it. (Pressed hard enough the pastic fan edge showed a tad of wear.) That sounds good.
- no whooshing or cycling observed when hot, though. Measured air speed, pretty constant (at 15 mph at a spot next to the head gasket in front if you wonder).
So overall this would suggest it's likely OK?
I wanted to come up with a better/easier/safer test with some numbers. Sooo,
I did some measurements with an anemometer and saw little difference in air speed from start to quite some time after steady state temp was reached on the dash, up to about 160F on the top rad hose, and about 125F on the clutch itself (about 20 mins idling). So that's not useful.
Tried to see if I could do something with a trigger gauge. But that doesn't work cuz the force is a function of speed obviously and there was no measurable yield stress. Not useful.
So I did the following, maybe this will help others as a "standard" test if it pans out:
I put a mark on one blade.
With engine stopped (obviously) I then tried to spin the fan by pushing on one blade to make it turn/freespin as fast as I could. When cold (clutch at 90F), even after rapid successive attempts, the blade turned consistently about 1 1/2 to 1 3/4 turn and you could see it spinning fast readily at least one turn. Then when I did it again when hot (150F see above) it would spun only 1/2 turn at the most. Somebody with a bad one could see if it's different?
So, summary:
cold (90F): freespins 1 1/2 turn
hot (20 mins idling) : freespins 1/2 turn
FWIW
HTH
thanks for the above.
here is my situation:
- no overheating problems noted
- no whoosh on cold start that I could tell, though. That doesn't seem good based on above.
- with engine fairly cold (clutch shaft at 90F), right after engine start I pressed my fingertips (with glove) against the rear of the fan blades. Pressed as hard as I was comfortable doing and the fan did indeed actually stop fairly readily. That seems OK if cold. Tried again when hot (150F at the fan shaft, after 20 mins of idling, upper rad hose at about 155F, air coming out of shroud at 150F or so), I pressed much harder than before and as hard as I was comfortable, and the fan slowed down a bit but I could not stop it. (Pressed hard enough the pastic fan edge showed a tad of wear.) That sounds good.
- no whooshing or cycling observed when hot, though. Measured air speed, pretty constant (at 15 mph at a spot next to the head gasket in front if you wonder).
So overall this would suggest it's likely OK?
I wanted to come up with a better/easier/safer test with some numbers. Sooo,
I did some measurements with an anemometer and saw little difference in air speed from start to quite some time after steady state temp was reached on the dash, up to about 160F on the top rad hose, and about 125F on the clutch itself (about 20 mins idling). So that's not useful.
Tried to see if I could do something with a trigger gauge. But that doesn't work cuz the force is a function of speed obviously and there was no measurable yield stress. Not useful.
So I did the following, maybe this will help others as a "standard" test if it pans out:
I put a mark on one blade.
With engine stopped (obviously) I then tried to spin the fan by pushing on one blade to make it turn/freespin as fast as I could. When cold (clutch at 90F), even after rapid successive attempts, the blade turned consistently about 1 1/2 to 1 3/4 turn and you could see it spinning fast readily at least one turn. Then when I did it again when hot (150F see above) it would spun only 1/2 turn at the most. Somebody with a bad one could see if it's different?
So, summary:
cold (90F): freespins 1 1/2 turn
hot (20 mins idling) : freespins 1/2 turn
FWIW
HTH
as far as the cause of the whoosh, here a couple of thoughts:
- we can probably disregard the effect of temperature changes during the first few seconds, first because there is no way the engine heat would affect the fan clutch in just a few seconds, second because any heat generated internally in the clutch by viscous dissipation would be first small and second would not likely lead to any significant temp increase in the fluid for several seconds I would think.
- Now there are 3 main types of viscosity changes in fluids:
1. Viscosity changes with temp. Usually it would decrease as temp increases, but obviously in this case they must use a fluid that has opposite trends (viscosity increasing with temp increasing) if they want the fan to turn faster if the temp goes up. Based on the assumption above this would have no effect on the whoosh.
edit: if, as TRU mentions below, there is temp actuated valve, then they may not need to use a weird fluid. Still probably not temp the main whoosh reason here.
2. Viscosity changes with shear rate. The viscosity can increase with shear (speed difference between surfaces if you wish) this is called a shear-thickening or dilatant fluid. Opposite is shear-thinning or pseudoplastic. The difference would be seen as how fast the fan reaches it's steady-state speed from 0 if you hold the engine at a constant speed. Likely longer in the shear-thickening case and vice-versa. This probably not the issue here cuz the fan speed apparently decreases at the end of a lengthy whoosh and this effect would only affect the dynamics of the unsteady period.
3. That leaves us with the effect of shear time on viscosity. A fluid whose viscosity decreases with time as it is sheared is called thixotropic. Opposite is rheopectic. This is what I think must be happening here. The fluid in the clutch is probably thixotropic. So after you start the engine, the fan increases quickly to speed (say a second or 2?) then it is continuously being sheared. This fluid is obviously highly non-Newtonian and so likely highly structured. After a few seconds, say the 15 secs mentioned above, the cumulative effect of shear over this duration is such that the viscosity decreases, perhaps rapidly. At this point the fan speed will also decrease and the whoosh stops.
Just conjecturing...
Of course, the arguments above are muddied by the change in engine speed to idle during the first few seconds. Also could be weird things happening with that "valve" or oil having to fill something etc in which case the fluid properties above may not be the predominant effect. Wish I could hear this whoosh.
- we can probably disregard the effect of temperature changes during the first few seconds, first because there is no way the engine heat would affect the fan clutch in just a few seconds, second because any heat generated internally in the clutch by viscous dissipation would be first small and second would not likely lead to any significant temp increase in the fluid for several seconds I would think.
- Now there are 3 main types of viscosity changes in fluids:
1. Viscosity changes with temp. Usually it would decrease as temp increases, but obviously in this case they must use a fluid that has opposite trends (viscosity increasing with temp increasing) if they want the fan to turn faster if the temp goes up. Based on the assumption above this would have no effect on the whoosh.
edit: if, as TRU mentions below, there is temp actuated valve, then they may not need to use a weird fluid. Still probably not temp the main whoosh reason here.
2. Viscosity changes with shear rate. The viscosity can increase with shear (speed difference between surfaces if you wish) this is called a shear-thickening or dilatant fluid. Opposite is shear-thinning or pseudoplastic. The difference would be seen as how fast the fan reaches it's steady-state speed from 0 if you hold the engine at a constant speed. Likely longer in the shear-thickening case and vice-versa. This probably not the issue here cuz the fan speed apparently decreases at the end of a lengthy whoosh and this effect would only affect the dynamics of the unsteady period.
3. That leaves us with the effect of shear time on viscosity. A fluid whose viscosity decreases with time as it is sheared is called thixotropic. Opposite is rheopectic. This is what I think must be happening here. The fluid in the clutch is probably thixotropic. So after you start the engine, the fan increases quickly to speed (say a second or 2?) then it is continuously being sheared. This fluid is obviously highly non-Newtonian and so likely highly structured. After a few seconds, say the 15 secs mentioned above, the cumulative effect of shear over this duration is such that the viscosity decreases, perhaps rapidly. At this point the fan speed will also decrease and the whoosh stops.
Just conjecturing...
Of course, the arguments above are muddied by the change in engine speed to idle during the first few seconds. Also could be weird things happening with that "valve" or oil having to fill something etc in which case the fluid properties above may not be the predominant effect. Wish I could hear this whoosh.
When I first start up my 97 with climate control it takes a few secs for the AC to kick on. Even then it starts out on low and then works it way up to high. I hear no fan whooshing. Just thought I would add this in.
I was just throwing this out since it seems to have gotten worse since my fan clutch went out. Maybe this is just my imagination. I remember I used to hear the fan whoosing and now it is gone also. AC used to be colder and now its not. Also Robbies fan test is not as bad as it sounds. I was kinda scared about doing it at first but it sounded like the best way to test it.
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The fan "clutch" works as an oil pump, pumping oil from one side to the other inside it, with a valve operated by the bimetal spring on the front providing the restriction. When cool the valve is open allowing the fan to almost freewheel, as the spring/truck warms the spring closes the valve making it harder to pump the oil, transferring the power to turn the fan.
The startup "whoosh" is probably the cold oil causing some drag until it's warmed up?
The startup "whoosh" is probably the cold oil causing some drag until it's warmed up?
well, I've now done several trials with stopping the fan with the engine idling.
Nothing much to it really. And not very dangerous I think (but don't blame me if you lose fingers). I use a leather glove, position my fingers tangential to the fan motion, and slowly apply pressure to the back of the fan. I have to push pretty hard and the fan will hit your fingers some, but it did stop when cold and it doesn't hurt at all. When hot, it did not stop even with fairly hard pressure.
In contrast, doing this while somebody starts the trucks seems pretty iffy to me. Would be easy to let go and get wacked. I like the above technique much more. In fact, won't even try the second one. I think if you are smart enough to not suddenly stick a finger in the fan, the worse thing that could happen is that your glove flies off and jams up the belts or something (not good admittedly).
Nothing much to it really. And not very dangerous I think (but don't blame me if you lose fingers). I use a leather glove, position my fingers tangential to the fan motion, and slowly apply pressure to the back of the fan. I have to push pretty hard and the fan will hit your fingers some, but it did stop when cold and it doesn't hurt at all. When hot, it did not stop even with fairly hard pressure.
In contrast, doing this while somebody starts the trucks seems pretty iffy to me. Would be easy to let go and get wacked. I like the above technique much more. In fact, won't even try the second one. I think if you are smart enough to not suddenly stick a finger in the fan, the worse thing that could happen is that your glove flies off and jams up the belts or something (not good admittedly).
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e9999 - are you retired - lots of time 
It sounds like your fan is fine - if you can't stop it when it's warm, I think that's the acid test. I also agree to only do the 'slow the fan down' trick with your hand when the truck is running vs on a start.
Cheers, Hugh
It sounds like your fan is fine - if you can't stop it when it's warm, I think that's the acid test. I also agree to only do the 'slow the fan down' trick with your hand when the truck is running vs on a start.
Cheers, Hugh
CDN_Cruiser said:e9999 - are you retired - lots of time
It sounds like your fan is fine - if you can't stop it when it's warm, I think that's the acid test. I also agree to only do the 'slow the fan down' trick with your hand when the truck is running vs on a start.
Cheers, Hugh
working at night. No sleeping. Yawwnnnn.
Yup, feeling better, seems to be in decent shape even if no Whoosh to be heard.
I went out and drove the truck around for a while tonight then tried to stop the fan -- No dice couldn't stop it at all. Still, no "woosh" though.
After driving around a bit I tried to stop my fan using a rolled up bunch of shop towels. Couldn't stop mine at all and now I'm covered with little bits of red cloth. No woosh here either. I would have tried again with some leather gloves but I don't have any.
No woosh here either. I would have tried again with some leather gloves but I don't have any.
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Well me, yea yea, I go and grab a six to seven inch diameter coniferous tree trunk, jump up and straddle the block facing forward (Important Note: Do not use the upper rad bypass bung as a foothold - everyone knows to use the shock towers, sheesh) and after carefull aim jam it into the fan blade at a straight 90 degree angle!
TurboCruiser becomes TurboChipper flipoff2: 
TurboCruiser becomes TurboChipper flipoff2:
anybody could try the freewheeling test? (esp. somebody with a known bad clutch!)
if the numbers are repeatable, we may have a quick and easy test that does not involve putting your hand in a spinning blade...
test conditions:
spin fan as fast as you can by pushing on one blade one time (flick o' the wrist kinda thing)
do it first cold and then after 20 mins idling or equivalent drive
note number of turns freewheeled in each case
TIA
if the numbers are repeatable, we may have a quick and easy test that does not involve putting your hand in a spinning blade...
test conditions:
spin fan as fast as you can by pushing on one blade one time (flick o' the wrist kinda thing)
do it first cold and then after 20 mins idling or equivalent drive
note number of turns freewheeled in each case
TIA
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The oil is distributed in the unit by centrifical force, so a static test will tell you very little. If it free spins when the motor is off it's out of oil.
LandCruiserPhil and I have started autopsying and testing some units, taking them apart to inspect construction, oil level, reassembling and mounting in the lathe, spinning them up and heating with a heat gun to check performance.
They work as an oil pump, but opposite the way I initially thought. When sitting the oil settles in the lower part of the unit, when it starts spinning most of the oil is pumped into a reservoir behind the valve, causing the startup whoosh. The "pump" is starved of oil allowing it to almost freewheel, as it heats up the valve progressively opens allowing the oil back into play transferring power to the fan.
The "blue hub" Aisin (the latest unit from Toyota) is the nicest one we have seen, very high quality machining and construction, so if you need to replace one buy with confidence from Cruiserdan! One of the unique thing about it is that the valve plate is adjustable, probably to set when it kicks in. this is yet to be tested, we need to aquire some of the silicone oil most of the units we have are low.
The failure mode we are seeing is low on oil, everything else looks good. Only one appears to be leaking, so where is the oil going? How much oil to add? Too much and it will be locked all the time, not enough and it won't work. How will adjusting the valve affect it? Will thicker oil make it lockup tighter? These are some of the questions we are going to make a feeble attempt at answering, will publish a web page when done complete with 26 glossy color pictures with lines and arrows.... Well, that song is 26 minutes long, so...
