I want to flush my coolant today on my 1988 420sel. I'm trying to find the radiator coolant drain and I can see two plugs at the bottom. One of them is black with three sections cut out and one of them is blue with an X in the middle.
I know I could just open them up and find out but I just had my transmission filled yesterday and I don't want to drain it.

Thanks for your time

Peter
1988 420sel
1988 300e