At 07:24 PM 7/27/2013, neil n wrote:
>No. Haven't heard my "1.9" 2 spd. fan kick into high speed but do
>understand that the noise level is somewhat noticeable.

Ours are just loud.  The big ones are louder.  Same size fan, half
again the power.  But you can hear yours any time by back-probing the
thermo switch connector on the radiator with a paper clip.  It won't
get hot, the high speed is relay-driven.

As to the research, the first stage is to document the resistance and
running current and power dissipation of the existing setup at its
various speeds, and I reckon the next one is to hit the back room of
a Friendly Local Auto Parts Store with a meter and a thoughtful
eyeball.  Or start winding your own.  And this could be a good
candidate for a PWM (pulse-width-modulated) control which might be
easier for some of us to work with than.  But until you know what the
existing setup is doing it's all mud.

Yrs,
d