Thread: Discovery 3.9 viscous coupling

Just thought I would share my experience with running high engine temperatures on the V8 3.9 during this past summer.
When switching off engine after running up the mountain (Dandenong Ranges Victoria) where i live the AC electric fans would continue to run for a short period of time.
This was a recent condition as last summer no issues.
The temperate gauge was always indicating in the middle of the range however when connecting Rover gauge the temp was in the high 90 deg range. Average speed 65kph.

Original radiator re cored and thermostat replaced in late 2024.
Checked viscous coupling which roars at cold and then tested when hot with the cardboard to stall fan technique which it seemed was powering the fan ok.
Also heated the bi metal coil on the front of the viscous coupling and observed it actuated the internal valve. Not oil leaks on the coupling housing'

Decide to purchase a new viscous coupling as no other options where jumping out.

All I can say is what a difference the new viscous coupling has made.
No high temperatures when pulling up long hills in above 35 deg conditions.
When the engine gets to approximately 75 deg the fan cuts in hard which you can hear roaring which also saps a bit of horse power.

I have for may years read numerous posts about overheating issues with the rover V8 and just would like to emphasize the importance of the viscous coupling.

AFAIR most VCs are set to activate at 94C.
If you have an 88C stock thermostat the thermostat is just fully open at 94/96C.
94C to 100c is absolutely nothing to worry about.
Regards PhilipA