Right... I just put my viscous coupling in the oven! Sounds daft but I wanted to check it locked up when it got hot. However, the hotter it got, the easier it was to turn by hand. To me, this sounds like a bust viscous coupling. Any thoughts?

Well I'm staying out of this one 'coz I haven't got a clue!

Viscous-type fan clutches provide a certain amount of fan control. Here, a bimetal strip on a fan hub senses temperature changes of air passing through the radiator. The strip connects to a valve that directs fluid to a fan clutch. High temperatures engage the clutch and low ones disengage it -- well, almost. Engaged viscous-coupled fans typically slip about 5 to 10% of shaft speed. And disengaged fans may still run at about 45% of engaged speed, especially at low engine rpm, says one SAE/DOT study. This inability of the fan to fully disengage can cause overcooling and may rob about 5% of engine power. Moreover, lowered coupler-fluid viscosity (from normal engine heating) delays clutch response which further degrades efficiency.

from machinedesign.com

 

OK Trevz looks like you are partly right:) Except I dont think the oil gets thinner as it gets hotter. Its the other way round - lowered copler fluid viscosity with heating.

 

I had thought the clutch locked up solid with the bi metal gizmo but it just changes the slip from the maximum slip to the maximum drive - 90 - 95 % of pulley speed.

 

You learn somat new every other day here!

 

So Mike any nearer sorting the overheating?

[OK Trevz looks like you are partly right:) Except I dont think the oil gets thinner as it gets hotter. Its the other way round - lowered copler fluid viscosity with heating.]

 

Hey willieo , i think u meant to type thicker where u typed thinner above? this is getting confusing lol.

My understanding is, the oil (silicon oil) doesnt get thinner or thicker as it gets hotter per se, but related to the heat of the engine yes it gets thicker.

It gets thicker thru velocity ie. when the fan spins same speed as the drive wheel the oil is thin , as the revs increase the wheel spins faster than the fan and the velocity thickens the oil. my brother is a mechanical engineer and specialises in hydrodynamics , damn, i got this shit from him :duffer: :xxx:

Anyway Mike, hows your Z?

Nah Trevz. Its nowt to do with fan speed or velocity in that sense. The way it looks is the bi metallic coil changes the twist on the clutch valving gizmo and that changes the slip rate allowed. The oil doesnt get any thicker. There's maybe some vanes or something in the coupling that drag more as the valving changes with temperature. So the oil still gets thinner as it gets hotter as most oils do but the drag on the coupling changes because the spiral bimetallic spring alters valving or something.

 

See what your bro says ;)

 

Defo agree with you here

As the rad gets warm, bi metal spring heats up and turns arm in housing which moves the oil plate and lets more oil flow between the grooves, giving stronger connection between wheel and housing.

Apparently reasons for slow fan are,

1 loss of oil

2 bimetal spring fault

3 siezed oil plate

 

Just dont agree that the oil thickens up - it thins but thats beside the point

 

We should have had this discussion wiv our anoraks on in the pub!

LOL willieo, so what colour's yours?

My anorak is yellow with removable hood , had to match my Z :tongue:

Bro gave me this link , check it out ,

http://www.roversd1.nl/sd1web/viscofan.html

I think they're simalar .

Anyway, i still think its the problem mikes Zed's got, hey , wheres he gone?

Have we bored him to death? lol

MIKE, u sorted it yet?

LOL willieo, so what colour's yours?

My anorak is yellow with removable hood , had to match my Z :tongue:

Bro gave me this link , check it out ,

http://www.roversd1.nl/sd1web/viscofan.html

I think they're simalar .

Anyway, i still think its the problem mikes Zed's got, hey , wheres he gone?

Have we bored him to death? lol

MIKE, u sorted it yet?

Sorry boys! Still here. Not sorted it yet as I'm more concerned with sourcing the split PAS pipe I've now got! I think I'll keep that to another thread!

 

Tried bleeding the cooling system today though to see if there were any air bubbles in it. Took the rad cap off and ran the engine for a bit. The level just rose ever so slightly and dispelled a small amount of water. But after a while (about 10 mins), some air bubbles started coming through. I hadn't expected to have to run it for this long to see any. Any thoughts on this? This carried on for 3/4 hour. Eventually, I had to stop as I had to be somewhere else. So I'll see if there's any improvement tomorrow.

 

Cheers guys.