The last time I saw that on my 300E, it was time for a new coolant pump.

Ironically, the coolant weeps out of the coolant pump and drips onto the block. It is very difficult to trace, and yes, the pump looks bone dry.

I had to wipe off the area and just stand there for several minutes and wait for the trickle of coolant to show up. Sure enough, eventually, it did, and when I placed my hand near the source, I caught drips coming from the pump (where you can't see it of course).

Mine didn't just collect on the belly pan...it had begun to puddle on the garage floor...

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car