I can't find the data anywhere and don't have a scanner. Does anybody know the exact temp when the fan cycles on? According to my temp gauge it's 64°C or 147°F, but I don't think that's quite accurate.

It turns on 1 tick below 1/4 on the gauge.

Temp gauge picture

(This is for an '89 L98 if it matters.)

 

147 is WAAY too cool for the motor and the ECM wont go into closed loop at that temp. my fans come on @176 which is where the ECM goe into closed loop.
on a stock setup it should come on around 220 but on my 89 formula they came on stock at 235 which is WAAAY too hot. i changed all of that by installing a 170 stat and on @176 off @166 fan switch.

 

Well I ended up emailing Hypertech. Apparently they turn the primary fan on at 176° and off at 166°. Same as their optional fan switch. Handy to know. They mentioned the temperature gauges are notorious for being inaccurate. Especially with the 160° stat combo.