It should be possible to cruise an aircraft at a reasonable altitude with the radiator flaps fully closed. The combination of high speed and moderate power (AND low temperatures in the simulated region) will allow for sufficient cooling.

All I manage in any CoD aircraft is a ruined engine 20 seconds into a 'Quick Flight' if I forget to immediately open the Radiator Flaps.

To the OP: The issue you describe could also be related to your propeller pitch setting and the speed you travel. You can overspeed your propeller in a dive and effectively cause the engine to cycle so fast that it shakes/burns to oblivion.

Pitch control in a dogfight is half the battle - Keep the RPM below the red line at all times

I do confirm. You might hve to watch closely your rpm that can be dropped bellow the recommended settings in these conditions

Hi guys. Is it correct that OIL radiator is not controllable? Or at least it seems so in the hurricane
Ciao

It all depends on the aircraft you are flying. If it has dual radiators (like the 109) you get two controls to use, if it has a single radiator like the Hurricane does you only use the water radiator commands.