I have a 1995 C280 with 120,000kms. About 8 months ago, I noticed the coolant/rad light come on intermittently when the car shifted (ie) up hills, around corners. I added a little coolant and it was fine. Now it's happening again. It happened on and off on my way to work this morning (about 30km trip) when I got to work I checked under the hood and there didn't seem to be anything in the over flow. Not sure how quickly it is removed from the over flow when the car is turned off though.
There's no visible leak, I've been checking. I'm going to top it up again but I'm wondering if there's something wrong with the cap and maybe it's slowly evaporating or it's a sensor.

Should there still be some coolant in the over flow when I shut it off? It looked dry...

Where should I start?

 

The over flow should show coolant when the engine is stopped and cold. Add a 50/50 antifreeze mixture until you get the level up to normal, it may take a few times to purge all the air out. Then monitor the level for a few days or weeks to see if it goes down. If it goes down then have the car checked for leaks.

Bill