Greetings all. Recently bought a 2005 S320cdi and have a very annoying coolant leak. I was driving perfectly fine when the check coolant light came on. Didn’t think anything of it so carried on home, let her cool down and checked. Expansion tank was at its lowest so o topped her up to the line and thought nothing of it. Next day I checked before I fired her up and the level was the same so I drove off. I then drove about 15 miles without problem and parked up. Came back the next day and the coolant was down to minimum again. I have started the engine and let her run up to temperature to get the coolant pressurised and flowing but cannot for the life of me see a leak anywhere. Also ran it with the expansion cap off to make sure I got any trapped air out but still it’s disappearing- would anyone have any pointers /experience of this to save me stripping the whole coolant system down please? Thanks in advance!

Welcome! Please post a photo of the S-Class. Try posting the question in the W220 section.

did you check the ground to see if there is coolant on the ground

Yep - can't see a thing. Also checked water pump and upper and lower radiator hoses. It's a proper mystery!

If there is no water on ground then that usually means that the coolant is getting into the engine block. It is coming out through the exhaust. Very expensive fix. I would have a mechanic check it out. Sorry