An operating temp. of 170 degrees should be plenty hot enough to get heat out of the heater unless there is something wrong with the heater. Check the heater control valve that is in the hose that runs from the intake manifold to the heater for proper operation. If it won't open it won't allow the hot water to circulate though the heater. If the valve is vacuum operated check the vacuum solenoid. My 40 Ford pickup with an aluminum radiator and a 160 degree thermostat would never get hot enough in the winter to get any heat out of the heater. As soon as the thermostat opened the temp would drop like a hot rock. I switched to a 180 thermostat and then it worked fine. In the summer that truck would run at 180 to 185 all day long with the AC on. Griffen aluminum radiator with 1 1/4 tubes, Walker fan shroud and a 17" steel blade mechanical fan.

Allen