Testing viscous fan coupling

#1
I'm restoring a 3500 with factory air con. I understand that the viscous coupling should be tested ideally with the engine running and warm. The car is in bits at the moment so is there any way I can test the coupling?
 

clive P62

Active Member
#2
Hi not normally.
If you bolt fan assembly to pump and hold pump so that it doesn't turn fan blades should have some resistance i.e.
not spin freely.
They were ment to start slipping at approximately 2500 rpm
Clive.
 

roverp480

Active Member
#3
I understood that initially there should be resistance to turn when cold , but when running it should settle down to virtually freewheel until the air temperature passing increases. Then when the air temperature through the radiator rises the viscous unit will stiffen up to start driving the fan. So on the bench it should show considerable resistance to turn the fan relative to the drive .
 

clive P62

Active Member
#4
The SD1 vitesse I had free wheels and if you keep revs up untill hot you can hear fan speed increasing to the point fan appears to be locked, then starts to slow again.
The p6 doesn't work that way on my dad's and my nada.
Clive.
 

roverp480

Active Member
#5
Thanks. I must admit I cannot get my head round the fact it slips at a certain speed, the whole point I thought was to work on load and temperature but I am not really knowledgeable about all the various types I have mainly been involved with drive train ones on Freelander / range rovers, plus the fan on my Discovery 3.
 
#6
Ok thanks. Mine is goosed then. It's as free as the pump pulley. I've seen the odd one come up on eBay for big money but I seem to remember they were the same part as one from a Land Rover. Can anyone confirm this?
 

colnerov

Well-Known Member
#7
Thanks. I must admit I cannot get my head round the fact it slips at a certain speed, the whole point I thought was to work on load and temperatu
re but I am not really knowledgeable about all the various types I have mainly been involved with drive train ones on Freelander / range rovers, plus the fan on my Discovery 3.
Hi, Don't worry you're not the only one. There's a member on another forum who can't get his head round the fact that they are some that are not temperature controlled. He also seems to resent it and even insists the manufacturers don't know what they're doing.:rolleyes:

Colin
 

SydneyRoverP6B

Well-Known Member
Staff member
#8
The water pump that accommodates it along with the pulley and fan are quite different to the fixed fan water pumps.

A distinguishing feature is that the P6B item features 4 threaded studs to retain the fan, whereas all the LR items that I have seen don't.

Ron.
 

GRTV8

Well-Known Member
#15
Some person with more knowledge than myself has stated you can repair the viscous unit by replacing the oil in it.
This I think involved drilling a hole in the unit and then plugging the same hole after re-oiling. Perhaps a google search ?
 

GRTV8

Well-Known Member
#17
Whatever way you go - could you post on here .
I have a viscous unit too and would like a back up story that works.
 

SydneyRoverP6B

Well-Known Member
Staff member
#18
Here is a NOS item that I purchased many years ago. The main visible difference between the P6B coupling and the LR coupling is the means of retaining the fan. Studs on the former, threaded holes I presume on the latter.

The rear illustrates the two keys that locate the coupling into the pulley. (I wonder if Holset the manufacturer in Huddersfield can be of any assistance?)

Ron.
IMG_1745r.jpg IMG_1746r.jpg
 
#19
That's very much for all the information. I favour the Land Rover modification route and will post any updates here. I guess the next step i to remove my coupling from the pump and check the key way arrangement.
 
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