Either something is wrong with your Chinameter gauge, or its experiencing some sort of heat soak, or something else is wrong with your system. My Toyota thermostat starts to flow exactly when its supposed to, almost to the exact degree its stamped at. It will then quickly get too cool as the near ambient coolant in the radiator starts to circulate, fluctuating between 90C and 75C until it stabilizes at normal operating (88C) temp at which point it fluctuates very little.
In addition to that, our thermostat has a provision for allowing air to get past it while closed, so its a non-issue.
Stock is somewhere around 190, according to the range accepted in the TSRM.
DO NOT modify your thermostat because you think you're exceeding the capacity of the cooling system (I can pretty much guarantee you aren't if its working correctly), especially DO NOT run without one. The only thing you'll do is create tons of wear and EFI problems.