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The Bear
nissan
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2,407 Posts
Discussion Starter · #1 ·
Trying to find out how firm the viscous clutch on the fan should be when cold, how do you know when to recharge with fresh silicon.

If I hold the belt flange the housing is fairly stiff to rotate.
 

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nissan y61
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4,788 Posts
Block of the radiator as best you can. Turn on the A/C and rev the engine at about 2000 rpm for ten minutes. The VC should kick in during this time. If after 10 minutes no VC rotation has been noticed or a increase in engine sound like large amounts of air been drawn in then switch off and try to turn the VC in any direction. If it feel lose then replace it if its stiff to turn then its ok but you may still consider changing it if the engine has done 75k to 100K.

You can also get a heat gun like they use for putting window tint on your car or for peeling paint. Heat up the front of the VC (bi-metallic coil strip) the VC should start to get harder to turn if not then replace.

We also use probes on meters to see what temp the VC cuts in and out at.
 

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The nutty professor
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8,299 Posts
my way is a bit more tricky,

start the car and go for a quick driveto get the motor up to temp, when you first start the motor you should hear the fan roar quite loud for about 30 to 60 seconds then it quietens down if you dont hear the fan roar at all (with a few revs) then the clutch on the fan is faulty and low on oil, when you get back from the quick drive pop the bonnet and increase the revs , if you hear the fan drawing heaps of air hold the revs till the fan goes quiet (the fact that it is drawing heaps of air probly means the fan is working fine)

however , if when you pull up the fan is quiet and the fan doesnt start to pull more air with increased revs then what i do is grab a rag an wrap it around my hand and use my hand to stop the fan from spinning ( and i dont mean jam your hand into the fan ) just use light pressure on the rear top edge of the fan to slow it down , once you stop the fan from turning hold it steady with the light to medium preasure on the rear top edge , if the clutch is working properly you should feel it starting to pull and trying to turn the fan within about 30 to 60 seconds, as soon as it starts to want to turn let the fan go and give it a rev , you should hear the fan roar with increased revs

if the fan doesnt start to pull or want to turn then the fan is faulty and either low on fluid or the bimetalic spring on the front is siezed or out of spec (from over heating), the same if the fan doesnt want to turn till the coolant temp is very high

my backyard way of checking the fan
 

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The Bear
nissan
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2,407 Posts
Discussion Starter · #4 ·
thanks Oilrig, but I have it out of the car now - in my hand so to speak. and like all viscous fans I have seen it spins and pulls air all the time that the engine is rotating, just that "theoretically" you can just grab it and stop it from spinning, good luck with that theory, not going to try it, need all my fingers this week. As far as I am concerned it has "kicked in" as soon as it rotates on engine start.

The fan has well over 300K on it now, but still very firm to turn when cold, just reading the "Clutch Fan Reco" thread, great dissassembled pics, and you can see that that one has been leaking, whereas mine looks shiney like brand new, no signs of leaks.

Thinking logically about the clutch the silicon fluid should never degrade because it doesn't get hot enough, and if it doesn't leak it should never need changing, its a very stable compound, in that environment, after all look at viscous clutches in say a subaru's final they last for ooo,ooo of kms, with no issues in a much harsher environment. Nope I'm going to leave it alone. doesn't appear broke just replace the fan component.
Thanks for your reply
 

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The Bear
nissan
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2,407 Posts
Discussion Starter · #5 ·
Hah Itsa, we were at it at the same time, thanks good post, will put it back in and try it, but it roars for a bit on start then obviously freewheels, gets dragged around by fluid friction, till it heats up. Will try that when its back together. Just need to try and mod to fit the old GQ fan now. Might have to order one from fleabay - up the north coast should be a quick courier trip, but cheaper than Nissan.
 

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The nutty professor
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8,299 Posts
when you first start the car the fan will always spin fast and roarwith a few revs as the silicon fluid is thick, you need to think of the clutch hub as a pump that recirculates the oil, when cold the oil is too thick to flow easily through the pump creating drag and spins the fan, once the oil warms up it thins out and the oil can flow through the pump, the pump has one valve controlled by the bimetallic spring on the front , as this spring warms up it expands/uncoils and tuns the shaft in the middle and closes a valve inside the clutch/ pump, once the valve is closed the pump/ clutch locks up cause the oil cant flow
 

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The Bear
nissan
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2,407 Posts
Discussion Starter · #7 ·
Thanks again ITSA can't see that in the photos, must be that little black flat plate in the middle that covers a port. Off to but some bits now from Cleveland Nissan, cant get a lower rad hose from supa crap.
 

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GU IV 4.2
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990 Posts
What's the go if the fan roars all the time? Roars when you start it up and rev it but just keeps roaring as long as you hold the revs on. Seized up maybe???
 

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The nutty professor
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8,299 Posts
What's the go if the fan roars all the time? Roars when you start it up and rev it but just keeps roaring as long as you hold the revs on. Seized up maybe???

either siezed or the little spring on the front is stuck in the position that locks the fan
 
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