Here is a picture of mine. The probe goes right in the tank.
I just completed a trip to Puyallup (1600 miles round trip). I have a B engine without a thermostat. At an ambient temperature of 60 degrees the coolant temperature was about 145 degrees. For every degree rise in ambient temperature the coolant temperature goes up a degree. Thus at ambient temperature of 90 degrees the coolant was about 175 degrees. I also found that hills make a big difference. A steep hill can add up to 15 degrees to the coolant temperature. My maximum temperature was 189.7 degrees going up the steepest hill with an ambient temperature of about 90 degrees, 40 mph behind a big rig.
Bob