I would guess that your gages are showing high. Do you have any way to check them? Like boil some water and put the gage sensor in it to see what it reads.
Water should read about 210 - 212 when boiling.
I always test my thermostats in a pot of boiling water before installing them to make sure that they open fully.
Here's how we tested thermostats in the A/C lab:
Get the thinnest diameter of wire that you can.
Open the thermostat (boil it in water until it opens). Then put the wire in the thermostat and let it close on the wire so you can pick it up with the wire.
We had this nifty heated plate with a magnetic spinner (it looked like a cold tablet) and it would spin while the heater was on to evenly spread the temperature of the water that we placed in a jar.
After the thermostat cools down and closes on the wire put it in a jar filled with enough water to completely cover the thermostat. Then use the wire to hang the thermostat in the under the water of the jar, but not let the thermostat hit the bottom of the jar.
Heat up the water in the jar with a thermometer in it (we had nifty digital ones). When the thermostat reaches the given opening temperature, it will begin to open and drop in the jar. Record the temperature when this happens and that is your opening temp for your thermostat.
You may be able to rig up something at home similiar to this to test your thermostat. We called this the "drop test" for thermostats...
