Turned out my thermostat was not good. That's what looks like caused that problem of the built up pressure in mycooling system and caused the radiator nipple to blow. I'm so happy I found that out and replaced it.

I drained the entire cooling system and filled with the Prestone flush and water. Ran that through for 15 minutes with the heat on maximum setting and went for a short drive. Came back and drained that all out. The fluid was super clean! Then I filled with water and ran for 15 minutes with the heat still on maximum setting and drained that all out. Finally, I filled up with the MB antifreeze and distilled water and topped off with the Red Line Water Wetter. Good as new!

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1989 300CE Astralsilber/Schwarz
1992 300CE Schwarz/Schwarz