I have total control of both fans with my Accel Gen7 ECU, what on and off temps would be best with a 180 deg thermostat? I was thinking

primary fan on at 190 and off at 185 (should keep coolant between 185-190)
secondary on at 195 and off at 190 (only on when primary cant keep up)

Not a real big deal, but interested in opinions!

 

I'm running a 180 degree t-stat in my 91 Z28. I have my fans on at 195/205 both off at 185. I also put switches in where the ash tray is so I can manually turn them on if I want the car to run even cooler. I'm using a jet fan switch for what is normally the secondary fan, its now the primary since it comes on first. I had a custom chip burned and the ECM controls the other fan. Not sure if that is optimal but it does seem to work well.

With only a 5 degree window for your second fan I would be concerned it might turn off and on too much. I'd rather have the fan come on and stay on longer instead of cycling. You might need to experiment a little to see what settings you like best.

 

That's what PCMFORLESS did on my chip (told them I had a 180° stat). It works quite well. For the secondary, I have a 200/185 fan switch controlling that.

With the above setup, I find that the primary fan is on most of the time when I shut the car off. The secondary will be on during the summer months. It is on about 50/50 during the late fall/early spring. And the secondary will be off during the winter months. There are times during the winter months that both fans will be off when I turn the ignition off.

Overall, I think the primary 190/185 and secondary 200/185 is a nice blend of not on all the time (wearing out parts) and still keeps things right where they should be.