the temp rating of the stat indicates what temperature it will open/close, if the reading near it is 175 it likely won't be opening all the way .... I'd skip the sender in the block, there is no factory info for the temp there, and I'd use an infrared digital thermometer to check the actual temp at various places, what 2 different dash gauges say can be correlated to that actual temp, especially the thermostat housing, top of the core, and bottom of the core - if there's a drop top to bottom of the rad of around 20 degrees things are working
Bill
