That seems like a simple problem, but it obviously was not. That's the first double thermostat that I've seen. I don't know of any vehicle that's available in the U.S. that would use such a thing. Here, we just take the thermostat out and the thing runs cold...
we are usually dealing with 109, 112 degree days here, so 99.9% of cars have this done to them eventually. But, as you can see from this contraption, it basically broke the function.
It goes to show that to someone who only has a hammer, everything can be a nail. (techs in my case)