A few days after replacing my thermostat my 300m puked coolant again. The noise & steam are comming from below the A/C compressor. According to all the info I can find I am either looking at a blown head gasket or a blown water jacket core plug. Can these plugs just let go under pressure? I have no leaks until everything goes wrong. I also need some diagram of where they are located. I can not find any pictures of them in the Haynes. I have never checked these plugs on any vehicle. What is the procedure for doing so?

If the problem can not be traced to theplugsI am pulling the engine & trans.