Thermo fans are capable of doing a good job when set up correctly but as Dr Terry points out they still don't shift the air as much as the horse power draining clutch fan.
Either though should be enough to cool a mild 308. I would say you have issues somewhere else. The biggest cause is cavitation http://en.wikipedia.org/wiki/Cavitation where you are not expelling all of the air when when filling with inhibitor. The fill point needs to be the highest point of the cooling system and typically the cooling system when filling needs to be level. This though is no guarantee that all air pockets are dismissed and devoid of air. Pressure filling is an option. Other issues can be the wrong, missing or incorrectly installed thermostat. You should be able to see and test the temperature change via the gauge or via an inferred thermometer as the thermostat reaches it's opening point to do the water transfer.

Also make sure your heater is open when the filling is done.
Over advancement of timing can also be a cause of overheating.