Viscous Coupling

[Mike Wattam <101714.1343@domain.elided>]

One of our TSR members has just had a bad experience.

He knew his fan viscous coupling had seized, but continued using the car. 
He allowed it to rev to approximately 5,500rpm while driving it, when the
fan broke up and caused a lot of under-bonnet damage, including a fan blade
piercing the bonnet.

Therefore, I suggest that when you lift the bonnet for routine checks, you
also check that the fan blades revolve (cold) reasonably freely, but that
the viscous coupling bearing is not loose.  If there is any sign of ageing
cracks in the plastic fan, renew it.

Obviously, if fan blade failure happened with an open bonnet, it would be
life-threatening.

Somebody in this digest recently told me they had bolted up their viscous
coupling solid, sorry I can't remember who.  I view of the above, it looks
as though this practice is very dangerous, so either keep the revs right
down or do something more positive about it, like renewing the viscous
coupling and possibly even the fan.  Also consider buying Glenn Merrell's
fan cowl, this would have given some protection in the case of this problem
as well as giving much more efficient cooling.

Despite this problem, I still think the viscous coupling is far and away
the simplest and most power-efficient way of cooling the Stag.

Mike Wattam
Triumph Stag Register