How do you test fan viscous coupling??

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Jun 17, 2005
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It was 95 degF here in Sacramento today and I had the ac on towing my boat from the lake. The gauge read exactly normal at level (9:00). I was curious and tried turning my fan with the engine off of course and there was not much resistance. How do you check the viscous coupling?
 
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If it's working right you will hear the fan roar for 10 or 20 seconds when you start the cold engine, then it will fade away as the fan idles down.

I replaced the bad coupling on my 96 LX450 and noticed that the roar was back.

Personally, I have problems holding any rotating part of the engine, even with heavy welding gloves!

John Davies
 

Koffer

 
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John E Davies said:
Personally, I have problems holding any rotating part of the engine, even with heavy welding gloves!

John Davies
I wont tell you I do it w/o gloves, but everytime after it gets harder to type/grap things . I only got a a couple of more times before Im typing with stumps :D


Oh yeah I really do check them w/o gloves on but Im not too bright either :rolleyes:
 
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If you let the truck sit and idle on warm day, and the fan clutch is good, you will hear the fan cut on and off periodically. The roar at startup is also a good indication.
 
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John E Davies said:
If it's working right you will hear the fan roar for 10 or 20 seconds when you start the cold engine, then it will fade away as the fan idles down.

I replaced the bad coupling on my 96 LX450 and noticed that the roar was back.

Personally, I have problems holding any rotating part of the engine, even with heavy welding gloves!

John Davies

Ditto on all points.
 

Dusty

 
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i recently replaced my fan with a new one from cdan and i also experienced the start up woosh with the new fan and i too almost lost my fingers trying the fan hold method.
 
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I finally gathered the nerve to do the 'grab test' this weekend.

While it sounds awful, it's actually very easy to do (I did wear a leather glove). I turned the truck on, walked around to the fan and slowly let my fingers slow the fan down. I could basically stop and hold my fan with my pinkie - new fan clutch on the way

Cheers, Hugh
 
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CDN_Cruiser said:
I finally gathered the nerve to do the 'grab test' this weekend.

While it sounds awful, it's actually very easy to do (I did wear a leather glove). I turned the truck on, walked around to the fan and slowly let my fingers slow the fan down. I could basically stop and hold my fan with my pinkie - new fan clutch on the way

Cheers, Hugh

If the engine wasn't hot this is normal... :bounce:
 
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Robbie tested mine on my '97 with the finger-hold test, we (ok HE) determined it was bad, then I took the old fan clutch and drilled it out and put in bolts to lock it solid, so it never would slip and spun 100% of the time at full engine speed. I did that to see if I had any other problems, since if it would still overheat even with the fan spinning full then there was obviously other issues. I drove with my hacked/locked fanclutch for a few weeks, no overheating at all...and the good news was I had far less power now and the truck sounded like an airplane (seriously, with the fan spinning that fast all the time, it's really loud!).

I have that hacked fanclutch if anyone wants to put it in their's to verify their's is bad, I have no use for it..you pay shipping and it's your's.

I wasn't sure my nifty hacked fan-clutch would find all problems since you could have a marginal cooling system and having the fan spin that much (more so than even a good fan-clutch would spin the fan) then it could mask other problems, since it's pulling in so much air...but it was worth it for the airplane sound alone.. :D
 
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CruisinGA said:
If the engine wasn't hot this is normal... :bounce:

Good point - the truck was hot from a hwy drive and then I held it for ~5min with no engagement (and no start-up roar)

Cheers, Hugh
 

miked

 
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mabrodis, funny you should mention the bit about locking it solid. i just went out to test mine, determined it is bad, and thought about locking it up somehow. if you still have the one you bolted up, i'll take it. i'll pm you for the details on payment for shipping.
 

miked

 
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mabrodis, i sent you another PM.
i won't be needing your bolted fan clutch as i bolted mine up this afternoon.
the amount of air now coming through is amazing. i took it for a spin around the block to check the a/c and i was grinning the whole way. it got upto around 105 today and before i locked up the fan clutch, i'd would've hesitated to even bother with the a/c. now it's like a whole new system.
i will definitly replace the fan clutch within the week.

edited to add: i see you weren't kidding about the sound.
 

miked

 
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update:
when i drilled the hole, i never saw any fluid or goo come out. i figured, ah ha! it must have leaked out over the years.
well, this morning i go out to the drive way and find a new oil spot under the front. my first thought was maybe my bolt had come loose and shot through something. i think running it around town yesterday was enough to finally force the fluid out through the hole. just a heads up if anyone else is going to try this, see if you can drain it before you put it back on. it makes a pretty good mess under there.
sigh...
 

cary

 
 
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Just to add to the data pile. On my 1996, there is no startup woosh. Thinking it may be defective I checked it this weekend after driving about 15 minutes in 100f weather. I couldn't even get the thing to slow down (I have checked them before and know what a defective one is like). So just because there is no startup woosh doesn't mean it isn't working.

Cary
 

Rookie2

 
 
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cary said:
Just to add to the data pile. On my 1996, there is no startup woosh. Thinking it may be defective I checked it this weekend after driving about 15 minutes in 100f weather. I couldn't even get the thing to slow down (I have checked them before and know what a defective one is like). So just because there is no startup woosh doesn't mean it isn't working.

Cary
I don't get why it "should" come on with a cool motor to begin with. Doesn't the coupling engage in order to increase cooling? Why would you need increased cooling for a cool engine?

Me confused.
Rookie2
 

Curran

 
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So out curiosity, I went out to the cruiser last night after reading this thread. I opened the hood and started up the truck. The fan started spinning when the engine started, but I couldn't describe it as a "woosh." Then I reachend in and easily stopped the fan from spinning with my index finger (still attached to hand.) According to everything I've read above this means that I need a new clutch, correct? (97FZJ w/ approx 118,000 mi)
Thanks for the help!

Curan
 
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Curran - you need to let it warm up a bit as it shouldn't lock too hard until the truck is warm. Give it a good drive then try and hold for a few minutes and see if it takes off as it warms up (ie you need to hold it for a few minutes as well).

I replaced mine last night and I now hear the 'start-up wooooooshhhhhh' and the fan blows much harder now by a very material difference in my case. The replacement job is a very easy 1 bananna job.

Cheers, Hugh
 

e9999

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Could somebody please elaborate on a couple of things since I'd like to determine if mine is OK without losing a finger and I think this may be helpful to others as well:

- this start-up whoosh, this is something beyond the fact that the rpms are higher for a few seconds when you start cold, right?
- after the whoosh subsides with a cold engine, how long does it take for the good fan to start cycling, and how fast is this cycling?
- this new finger test, unlike Robbie's, is to have the engine start, wear a glove, and bring your fingers slowly in contact with the fan to see if it slows down, correct?
- perhaps most importantly, could somebody with a bad clutch (Curran?) and with a good one (CDN?) try and see what level of resistance there is if you try to turn the fan with engine stopped?

With this info, I may try to start measuring air velocity and maybe even fan velocity.

TIA
 
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The plastic fan is not made to turn full RPM long term, if you lock the fan clutch keep the revs down or you run the risk of the fan coming apart, taking out the shroud, radiator, denting the hood, IMHO not worth it.

- after the whoosh subsides with a cold engine, how long does it take for the good fan to start cycling, and how fast is this cycling?
Depends on how hot it is, you should not be able to hold it when the air is about 150 degrees in the shroud. With the truck warm, hold the fan, in short order you wont be able to hold the fan or the air will get too hot to keep your hand there! Keep screwing around and the truck will overheat.
 
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