Hello everybody! @FreeThinker I have the same problem as @ss8913. I pIay career mode in KSP 1.4.5.2243 and I have a craft with a 2.5m lightbulb engine, with hydrazine as fuel. It's on the way to the Jool system. For cooling, 4 Grafen Radiators Folding Large is used with maximum improvements (4400 K maximum temperature). This was more than enough earlier.
I updated from version 1.19.9 to 1.20. And now, if I give full thrust, the engine quickly overheats and begins to automatically reduce the thrust to about 20% to avoid an explosion. At the same time, the temperature of the radiator is about 800 K, the temperature of the part (fuel tank connected directly to the engine) is about 4000 K, which is strange, I think.
After returning to version 1.19.11, everything is working fine, as before.
So, is the waste heat system was some kind revised, or it is a bug?
English is not my native language, I use Google translator.