Thread: Viscous Fan. That old chestnut

Fluid type AFAIK Pete , not sure about the revs but once its locked it should be close if the pulleys are a similar size.

Originally Posted by land864

I have read a few things about testing the viscous fan but I'm not keen on poking a rolled up newspaper into it when operating
I fitted a brand new, complete fan about 9 months ago, and after hearing many times about the rolled-up newspaper trick, I decided to try it. Engine cold after standing overnight. Placed roll between blades of fan, stood directly in front, and held on with two hands while my wife started the engine. Couldn't hold it - the ends of the blades shredded the end of the paper roll. Tried again with the very end of the roll pressed against one blade, me standing behind the RHS headlight. Same result. Ambient air temp was in low-mid 30's C, but I wouldn't expect that to affect it much.

I think the fan is working OK, because I can hear a change in the sound it makes when the engine is working hard and/or the ambient temperature is high (like 40 C). I can easily turn the fan blades by hand when the engine is cold and not running.

I downloaded a strobe app on the phone to check the fan speed

Should the fan revs match the engine revs when the coupling is engaged?

For example, engine rpm at 780 rpm, fan at 780 rpm?

Engine at 2000 rpm , fan at 2000 rpm?

Are ours bimetallic or the fluid type?
The hub contains fluid whose viscosity increases as its temperature does, but it also has a (bi?)metallic coil on the front. As I understand it, this flat, spring-like coil expands with heat and acts to shut off internal bypass holes that the hub fluid can normally pass through under cooler conditions.

Cheers,
Andrew Milne

the rolled paper trick works well on the outer circumference of the fan (ie. the circle which encompasses the blades). Let dramatic and less to go wrong. If this stops it, then it's kaput.


As others said it's the fluid type with a metal coil on the front which controls the internal valve.


When locked up at idle, it'll run roughly at engine speed, but as the revs increase, it'll slip more and more due to the air resistance, so won't match revs.

If your cooling system is in good nic even on hot days it won't be operating a lot, but you should definitely hear the difference when it's engaged. Eg today, stop start driving in Melb at 38c ambient with the ac on, I can hear mine engaged for about 5 -10 sec after take off from idling in traffic only. Once moving along you won't hear it unless you load up the engine, eg up hill, towing etc.

How do I hear anything over the dulcet tones of that TD5
A bloke told me last week that the TD5 was originally a truck motor and before that a marine engine?

Originally Posted by land864

How do I hear anything over the dulcet tones of that TD5
A bloke told me last week that the TD5 was originally a truck motor and before that a marine engine?

He is what the spanish call a pajero.
http://www.landroverclub.net/Club/HTML/Td5engine.htm.
New engine design for Rover. Only got into Defenders and Discovery 2.

Originally Posted by land864

How do I hear anything over the dulcet tones of that TD5
A bloke told me last week that the TD5 was originally a truck motor and before that a marine engine?

maybe he was mixed up with the 3.3 i6 diesel patrol engine circa 1980. I believe it was used in trucks/forklifts/boats. Tough engine, very smooth, if gutless!

Originally Posted by D2lee

maybe he was mixed up with the 3.3 i6 diesel patrol engine circa 1980. I believe it was used in trucks/forklifts/boats. Tough engine, very smooth, if gutless!

More likely confused it with an isuzu which is like chalk and cheese, AFAIK the TD5 was a brand new design not a borrowed hand me down.