Hi everyone,
I'm quite happy with my CLS 500 Shooting brake and its M278 so far but I've had an unpleasant surprise already.

I've seen the coolant level low message twice in about 1000 miles. I've topped it off first time to the mark recommended by the manual and it already re appeared.
I need to buy a more recent coolant (first time was just before a big trip so i used an old can of coolant I had). Should I go with a MB specific coolant or any would do?

I don't think it's a head gasket failure as the oil is clean and I don't have any suspicious white smoke or bitter smell from the exhaust so I'm leaning towards a leak.
Do you know of any common place for it to leak or a quick procedure to look for it before I go to a mechanic?

Thanks.

 

The hoses running from the bottom of my radiator had a fair amount of surface rust when I changed my coolant recently. My CLS is two years younger than yours so assuming I had left the rust on for another two years, maybe that hose joint would have started leaking ? It is close to the radiator drain valve release which is on the drivers side of the radiator, at the bottom. Only visible when you remove all the under body shielding. Hope you find your leak.

 

Get the cooling system pressure tested...it'll show you exactly where any leak is.

 

Welp, garage pressure tested the system and... no leak.
We found traces around the filling cap so it may be leaving there but we're not certain

So it's a bit more worrying than I expected as the mechanic pointed to 3 possibilities:
1- Head gasket but feels unlikely as there is no gunk in oil, no smell in coolant and no apparent white smoke
2- Overheating of coolant leading to pressure in the expansion tank and evaporation going through. The gauge on the dashboard being steady and right between 80-100°C (175-210°F) but never going over half the distance (I think it's around 85-90°C so 185-194°F) it feels unlikely as well
3- Loose cap that would go into "safety release" mode too early and letting the vapor of coolant out at running temps.

I'll check with another mechanic who is better equipped to put a definitive answer to the head gasket as it's my biggest fear right now.

I'll keep that post updated on what comes next.

 

Get a Block tester kit. They're cheap and easy to use. You'll soon know if it's your head gasket.

 

If I had no warranty on the car, I'd have considered it but I'll go the standard mechanic route in order to avoid voiding it.

I'll go to the merc dealership in order to get a full diagnosis on that issue, they should be the most qualified around here.

 

Welp, she's back from 2 different garages and they didn't find the cause.
The car is leaking coolant continuously even when stopped but there is no visible leak on the floor, no particular white smoke and everything else seems OK. Everyone is a bit baffled with it and the last guys started blaming ethanol reprog even though I don't see how it could have such an effect.
I'll see how I proceed from here.