Incredible disappearing coolant trick

[seattle_Jerry]

I think about my 220D everytime I listen to cartalk. It had a problem that could just as easily have been on an SL and I never figured it out.

It could go for days or months without needing radiator fluid. I checked regularly and it wasn't a slow leak. It was always full to the brim until it was bone dry.

There was never a puddle under the car.

My guess is that there was a crack in the head or block that sometimes opened and let the water escape.

Any other guesses?

[merrill]

where was the puddle located?

could be a failing water pump or maybe your heater core?

did the fluid show up after you ran the heater ?
what was the outside air temp?

[waqas]

I recently found a similar slow leak... which accumulated inside the car!  No leaks outside, coolant level would drop slowly over time. I recently found that the heater core bypass valve is the culprit (in my 250SEC). Found thin layer of coolant on the passenger floor board.

[seattle_Jerry]

Thats the thing...there never was any evidence of a leak. No puddles, drips, smell of coolant. It wasn't a slow leak. It was full or it was empty.