Viscous Fan. That old chestnut

**rapserv** · 30th September 2019, 04:48 PM

Originally Posted by D2lee

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.

I thought that the Viscous fan was meant to freely rotate in a cold engine .... allowing the engine to heat up quicker.
When the engine is hot (or hotter than it should be) it's supposed to lock up and provide extra cooling.
Have I missed something here?

**biggin** · 1st October 2019, 04:53 AM

Originally Posted by rapserv

I thought that the Viscous fan was meant to freely rotate in a cold engine .... allowing the engine to heat up quicker.
When the engine is hot (or hotter than it should be) it's supposed to lock up and provide extra cooling.
Have I missed something here?

The viscous fan is not free at startup even if cold. With no movement, the fluid settles and locks the fan. It quickly unlocks with centrifugal force until temperature gets high.

The motor heats up quickly due the thermostat being closed therefore taking the radiator out of the circuit. Nothing to do with the fan.

**AK83** · 1st October 2019, 06:54 AM

Originally Posted by biggin

.....

The motor heats up quickly due the thermostat being closed therefore taking the radiator out of the circuit. Nothing to do with the fan.

You'd be surprised!
When it's in the depths of winter here, I take the fan out of my D1(tdi), and she runs fine(around town).
I have(had) a specific route I'd use to get to work to get the main arterial road to get onto the freeway to work.
With fan still installed, but the time I got to the major road(Bell St), coolant was showing 53-55°C on almost any cold morning.
Cold morning would be anywhere between 1-13°C.
Remove the fan tho, and by the time I got to that same spot, coolant would show in the low 60's.
Never really timed it, but about 5 mins, including about 20-30sec warm up time while I rolled my rollie.

Thermostat fitted to the tdi is a Tridon 88°C version(190F), and having tested it, I know begins to open in the 80°C range(and I get a consistent 83-ish C coolant temp average) .. so thermostat does work fine.
I read comments re thermo fans can help with quicker warm up time(which I found to be true), so had plans and ideas to mod mine with fans .... when my viscous dies again.

**rapserv** · 1st October 2019, 07:25 PM

Originally Posted by biggin

The viscous fan is not free at startup even if cold. With no movement, the fluid settles and locks the fan. It quickly unlocks with centrifugal force until temperature gets high.

The motor heats up quickly due the thermostat being closed therefore taking the radiator out of the circuit. Nothing to do with the fan.

I replaced my viscous fan in the Disco 2 TD5 about 2 years ago because I was having issues with the car running too hot.
The original fan could be easily rotated with my finger. After changing it to the new fan ... I found that I could still rotate it easily by hand.
After getting the engine hot ... and I mean hot as in 104 degrees ... I can still rotate the fan easily by hand.
From what you are saying .... maybe my replacement fan was faulty as well from the start.

**biggin** · 1st October 2019, 08:37 PM

It should noticeably roar above the noise of the engine when rev’ed in the first 30 seconds from cold. If not, then yes, it’s faulty.

Thread: Viscous Fan. That old chestnut

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