[Seeker]

Going from the old IL-2, if you've set keys and an axis to the same function, the axis over rides the keys.

I'm using the default keys for this function, and it's working fine for me. You can confirm rad movement five ways:

An info window giving the rad position as a %, 100% being wide open
An info window showing control positions, the rad is the blue control, full up is full open
The operating lever to the right of the seat in cockpit
There's a position gauge to the left under the throttle
The Rad flap is quite obvious in the open position in the out side view, to the extent I can see if my squad mates have forgotten to close it for cruise.

And all of this only works if you have "CEM" (Complex Engine management) enabled.

If you're new to this, a high boost (throttle) setting warms up the water (rad), that's the green gauge, a high RPM warms up the oil (the yellow gauge). Adjust your flying to suit.

Edit: I've just noticed you say you have the heat effects disabled, you may have to enable them to get this to work.

I haven't experienced rough running in cloud in the Hurri yet. I think your diagnosis may be correct, and in real life (if not in game) richening the mixture would probably help.