Viscous fan prob

WURZAL THE LANDY · Apr 27, 2015

OK before I buy a new viscous unit as I have 2 fans both operate all the time at full speed. I am wondering is there some bodge the previous owner could have done to make the fans come on permanently?

Yes I know they should turn but you should be able to stop them with the rolled up news paper but my drive just ends up covered in confetti.

I bought the second fan used so don't know if it is also faulty in the same way as from what I read the fail more often by not working at all.

I only use tiny at the weekends so its not a huge problem just a little annoying as its on the todo list and would like to get it sorted.

How does the fan work? what heats up to tell the fan its time to start and can this stick open?

Grrrrrr · Apr 27, 2015

This is probably a really stupid question but you are testing with a cold engine?

stuu · Apr 28, 2015

Fans always spin. If the engines cold it takes a minute or so for the viscous to loosen then slip until heat of engine and off the rad heats up the viscous and it locks 'on' run the engine till needles just out the blue stick it in netrual and you should hear engine and slight fan noise and be able to stop it spinning. Then when engine is upto temp half way. Sit it in nuteral again and give it a hard rev you should hear the fan roar and not be able to stop it moving.

WURZAL THE LANDY · Apr 28, 2015

Yes engine is cold fan is on full blast from first start up

Stu let me see if I have got you right
1 start cold engine - fan on high?
2 run till temp increases a bit - fan now on low and stoppable
3 run engine up to half way on temp gauge and rev - fan on full again?

This dosent sound right to me.

Sorry for stupid questions but you say heat off engine and rad, I'm trying to trace a possible bodge. My thinking is to start fan it's:-
Engine block heats up
Heat transfer through water pump shaft to nut on fan
This then heats up viscous unit spring so it expands and locks on therefore full speed.

Bladerunner919 · Apr 28, 2015

WURZAL THE LANDY said:
My thinking is to start fan it's:-
Engine block heats up
Heat transfer through water pump shaft to nut on fan
This then heats up viscous unit spring so it expands and locks on therefore full speed.

That's true, but from cold, when the engine's been stationary, there's a short period where the fan is also kind of 'locked on' until the viscous fluid redistributes itself in the coupling.

To be pedantic, it's ambient heat from the radiator rather than the water pump shaft, hence the fins on the viscous coupling.

Datatek · Apr 28, 2015

WURZAL THE LANDY said:
Yes engine is cold fan is on full blast from first start up

Stu let me see if I have got you right
1 start cold engine - fan on high?
2 run till temp increases a bit - fan now on low and stoppable
3 run engine up to half way on temp gauge and rev - fan on full again?

This dosent sound right to me.

Sorry for stupid questions but you say heat off engine and rad, I'm trying to trace a possible bodge. My thinking is to start fan it's:-
Engine block heats up
Heat transfer through water pump shaft to nut on fan
This then heats up viscous unit spring so it expands and locks on therefore full speed.

1, 2 & 3 are correct, the viscous is operated by heat from the RAD, if you look at the centre front of the fan, you will find a Bi-Metallic coil attached to a shaft going into the viscous unit.
I hate to say it but I told you not to buy secondhand.
If your car is diesel and the cooling system is good, you can chuck the viscous fan and use my aircon fans mod, assuming your car has aircon.

WURZAL THE LANDY · Apr 28, 2015

Ok so maybe my fan was fine and I didn't need a replacement if so I'm putting it down to newbie inexperience. I will give it a go latter and see if it stops fingers crossed.

Datatek · Apr 28, 2015

WURZAL THE LANDY said:
Ok so maybe my fan was fine and I didn't need a replacement if so I'm putting it down to newbie inexperience. I will give it a go latter and see if it stops fingers crossed.

If the viscous is good, you cannot stop it with a rolled up newspaper when hot and even when cold it may mash it. The fan rotates at a fair lick even when the viscous is slipping as in the cool phase.

WURZAL THE LANDY · Apr 30, 2015

Bladerunner919 said:
That's true, but from cold, when the engine's been stationary, there's a short period where the fan is also kind of 'locked on' until the viscous fluid redistributes itself in the coupling.quote]

Well it seems it wont unlock I don't want to buy a new fan if this one is working correctly I'm getting a bit confused here with it should stop and it shouldn't?

brianp38dse · Apr 30, 2015

It will never stop turning, its the speed and force that changes.

WURZAL THE LANDY · Apr 30, 2015

brianp38dse said:
It will never stop turning, its the speed and force that changes.

yeah but it seem to be running full speed all the time

wammers · Apr 30, 2015

WURZAL THE LANDY said:
Bladerunner919 said:

That's true, but from cold, when the engine's been stationary, there's a short period where the fan is also kind of 'locked on' until the viscous fluid redistributes itself in the coupling.quote]

Well it seems it wont unlock I don't want to buy a new fan if this one is working correctly I'm getting a bit confused here with it should stop and it shouldn't?

Click to expand...

Fluid is stored in the centre of the hub. There is a valve in the unit that opens with heat and the fluid goes to the outside of the hub through centrifugal force, this causes a partial friction lock between two close fitting vane plates and drives the fan. When the engine stops fluid runs back into the storage area. But it cannot run back from the bottom of the hub. That is why on start up cold the fan will sometimes tend to roar for a few seconds before fluid is distributed and the drive reduces. Fan never stops. Cold it has minimal speed and is easily stopped, just being dragged around by the centre shaft revolving inside it, little air is drawn through the rad. When the radiator gets hot, heat from it warms the fan hub and opens the fluid valve and the fan becomes engaged drawing air in through the radiator.

wammers · Apr 30, 2015

WURZAL THE LANDY said:
yeah but it seem to be running full speed all the time

When the engine is stopped can you turn the fan? Maybe a little stiff for a couple of turns then should free off. If it is hard to turn with engine off and does not free off after a couple of turns you have a problem.

Carl1960 · Apr 30, 2015

Would it not be easier to fit an electric fan unit. I did that to my 2.9 XR4X4 which had a viscous with a control unit you can then control the fan start temp and also modify it to run on after the engine is turned off.

wammers · Apr 30, 2015

Carl1960 said:
Would it not be easier to fit an electric fan unit. I did that to my 2.9 XR4X4 which had a viscous with a control unit you can then control the fan start temp and also modify it to run on after the engine is turned off.

Depending on which you get a fan hub is between £30 and £70. How much is an electric fan kit? Kenlowes are not what they used to be by all accounts. Overheating a V8 Range rover is not something you want to be making an habit of.

Datatek · Apr 30, 2015

Carl1960 said:
Would it not be easier to fit an electric fan unit. I did that to my 2.9 XR4X4 which had a viscous with a control unit you can then control the fan start temp and also modify it to run on after the engine is turned off.

No need as the aircon fans already fitted can be adapted for cooling on the diesel.

WURZAL THE LANDY · Apr 30, 2015

wammers said:
When the engine is stopped can you turn the fan? Maybe a little stiff for a couple of turns then should free off. If it is hard to turn with engine off and does not free off after a couple of turns you have a problem.

I can spin it freely from the start its not stiff at all.

I'm not a fan of the electric fans as the worry is cooking the v8 engine I do plan to do the ac fan mod in the future once this is sorted

Datatek · Apr 30, 2015

WURZAL THE LANDY said:
I can spin it freely from the start its not stiff at all.

I'm not a fan of the electric fans as the worry is cooking the v8 engine I do plan to do the ac fan mod in the future once this is sorted

The mod is a good back up on the V8 but not a replacement for the diesel.
Your best option is to buy a good quality ie not ****part, viscous unit.

wammers · Apr 30, 2015

WURZAL THE LANDY said:
I can spin it freely from the start its not stiff at all.

I'm not a fan of the electric fans as the worry is cooking the v8 engine I do plan to do the ac fan mod in the future once this is sorted

4.0 litre petrol should already have a circuit to bring on aircon fans in case of overheat at certain times. Don't think you can do Keiths diesel A/C fan mod on the petrol.

Datatek · Apr 30, 2015

wammers said:
4.0 litre petrol should already have a circuit to bring on aircon fans in case of overheat at certain times. Don't think you can do Keiths diesel A/C fan mod on the petrol.

The standard set up only brings the fans on when an overheat is actually happening, my mod which works on all P38's and allows setting to bring the fans on at just above normal, long before an overheat occurs.

Viscous fan prob

Active Member

Technician, Bodgit & Scarper Ltd

Well-Known Member

Active Member

Active Member

Well-Known Member

Active Member

Well-Known Member

Active Member

Well-Known Member

Active Member

No longer with us, RIP

No longer with us, RIP

Member

No longer with us, RIP

Well-Known Member

Active Member

Well-Known Member

No longer with us, RIP

Well-Known Member

Similar threads