High Temp, Coolant Light

[96C280]

So I was driving in the c280 and the temp outside was maybe 83 degrees and I come to a stop quickly when the guy in front decides to stop suddenly (This may be totally irrelevant but....). So the light turns red and I wait. All of a sudden I hear noises from the center vent area like there is vacuum sucking and releasing and then sounds as if something is bumping around. Initially I think it's something wrong with the vacuum diaphragms of the a/c flaps. It sounded like from that area. So I think great. This goes on for about 20 seconds and I turn of the a/c. I don't remember if the sound went away immediately or the exact sequence, but I then notice the temp sensor has gone all the way to 120 and eventually touches the red area. I'm now thinking that something has blown in the cooling system. There's nowhere to stop until maybe another 1/4 mile and less than 10 minutes as I come to a stop I notice the temp is dropping but then the coolant/radiator light goes on. So again I think the cooling system has crapped out. Stopped the car, looked under the hood expecting steam and a pool of coolant or radiator or anything. But nothing, a little liquid around the expansion tank. Now I'm thinking that maybe it's completely drained and has evaporated since whenever. Can't see the level in the expansion tank because thank goodness (sic) mercedes decides to use amber coolant in a amber/beige expansion tank. Expecting things to be too hot, I wait until later. I come back hours later and pour about a liter of water into the exp tank. Start up the car and drive off. No noise, no light, good temp. Have driven over the weeken quite a bit with and w/o a/c and no symptoms. And no further adding of water/coolant as the expansion tank is almost full. Does anyone know what happened???

I'm going to change the expansion tank cap as it was badly worn in the rubber areas but could this have caused the symptoms. Again it sounded as if when a vacuum diaphrapm was having a seizure then as if a rubber ball was bouncing around, then very high temp, then radiator light. Now nothing?????