What temperature is your car running at with the 170 degree thermostat? You can find out by bringing up cylinder head temperature on the gauge cluster test/trick.
The link at the end of the article explains what you are seeing on the display.
I am reasonably certain that cylinder head temp is actually coolant temp.
My Mach 1 has the stock thermostat and according to the Scan Gauge II plugged into my OBDII port, my coolant temperature normally runs at 190F and a little higher on hot days. The temp gauge stays in the middle.
I think 180F is too cold. I'm wondering if your gauge is off.