I'm sure alot of experts out there already know this but:

Over the weekend I removed the mechanical fan setup on my 69 in favor of a dual spal setup with a spal 195* on temp switch. After installing fans, relay, wiring, and temp switch I fired it up expecting to see the fans come on at 195*. 200 no fans, 210 no fans, 220 no fans. Shut off car. Turn key on 30 seconds later fans come on. WTF.

To make a long story short, the fix to this issue was to pull the thermostat out and fill the block up to the base of where the tstat would sit and top off radiator (expansion tank). Fired-up, fans come on at 200*(maybe a slight calibration difference between switch and my temp gauge, close enough for me). There was either an air pocket or only steam passing the temp switch (mounted in hole in intake next to distrib on drivers side) and neither will trigger the switch even if the steam temp is well over the "on-temp" of the switch.

 

Where did you place the thermostat sensor???

 

Intake water port next to distributor on drivers side.

 

I just have my wires hooked up to the sensor on the radiator itself. Am I better off using the sensor installed in my intake? I've been having a similar issue, but not nearly that bad.

 

You need to move it to the upper radiator hose or thermo housing. That is the first area too get the hot water when the thermostat opens.

 

Are you sure there's coolant flowing back there ?