Hi All,
I am a little confused in why a thermostatic actuation switch would not be better. You can always add an on/off switch if it is your desire to control the operation at times and also a timer if long term run-on is a concern. However, if you are going to take advantantage of having a pusher fan, why not really take advantage and let it do its thing when it is needed and eliminate having it on your mind.
Also, as I have experienced when trying out a pusher fan, placing it in the common position in front of the radiator behind the grill creates a block in the path of the airstreem from grill through radiator. Although this block does not seem to create an adverse temperature problem at driving speed, it can cause the electric pusher fan to be needed at a slow running speed when normal air flow would be sufficient to cool the engine and would require the pusher fan be active more often then needed without it acting as a block.
I have mentioned my use of (2) forward low mounted AC auxiliary fans aimed upward at the radiator in my TR7 (without AC) that are the only cooling fans. I find this mounting to be very effective as the forward upward angle of the air stream intersects at an advantageous angle with the cooling fins of the radiator and allow an unblocked air flow from grill through radiator. The fans are thermostatic controlled (no thought on my part whether to use or not) and are also controlled by the thermostat or a timer (which ever hits its limit first) when the ignition is turned off. Although I have also installed an on/off switch as a safety precaution to deactivate the fans manually, it has never been used in over 10 years in use.
Sorry if I am being redundant or missing something others are not,
Ray(64BJ8P1)