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?????

96C280,

You did a great job explaining this situation. I just went through exactly the same symptoms this weekend and was thinking of how to ask the question. I have looked under the hood and nothing I can see could have caused the thumping sound.

The temp in my car (1993 300E) did not go quite as high as 120 degrees despite a 45 minute crawl through Santa Barbara, CA. But the sound came during the traffic crawl and again today during a short drive from work. This time the temp. was normal (under 90)

I hope we get a response from the MB masters.

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TOOFAST45

'93 300E 2.8 - 138K miles

Since the coolant temp gauge in the car does not move above 95C until the car is not too far away from needing to be shut off, it is possible that the temp was slowly rising over a period of time. In this case, you need to determine whether it is a coolant flow problem or an airflow problem. Were you in stop and go traffic for a period of time leading up to this or was it open air driving? Also, do you know if the aux fans are operating properly. The mechanical cooling fan cannot handle all of the cooling air requirements of the car in heavy traffic without the assistance of the electric fans.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record

Does it sound like this ?
http://www.club202.com/forums/showthread.php?s=&threadid=5819

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2007 C 230 Sport.

Wow. I think that's what it was. Unfortunately, the guy doesn't get into discussing what this does to the cooling system. I'll post there and see what happens. Maybe you guys know? In my situation, it seems that coolant flow was blocked, i.e., the eventual coolant light going on. According to the manual, it says it's a coolant level light but does not indicate it has anything to do with temperature. I think it doesn't, because by the time the light came on, the temp was no longer near the red. Could blockage/failure in the heater core be a potential?

P.S. These cars can kind of strand you for the weirdest reasons. I once lost all power and had to pull over on the freeway. It turned out some kind of switchover valve in the gas tank had failed. Thus I had gas, engine was fine, but it couldn't get the gas.

By the way, all the fans were doing their job as they were going on full bore (you could hear them) and not letting the temp go too far into the red. Ali, I don't know exactly what you mean.....95 is no where near the 120 mark on my gauge. I'm almost 100% sure this happened within a couple of minutes...at the most.

If fans are working , first suspect is bad cap.
Replace it and retry.
The car was low on coolant cuz the cap seal is bad and won't hold pressure .. the light came on cuz you were then low on coolant ..