W203 M271 engine - mystery coolant loss

[Remmoc]

And so the saga continues ever on
This time the mystery of the coolant dropping with NO apparent leak
Ive been topping it weekly to the top of the divider in the expansion bottle and over a week of shortish runs ( 10 miles per day ) it slowly drops.
Yesterday i checked it as normal and topped it up to the top of the divider - we did 80 miles yesterday in two 40 mile trips and this morning its dropped around 10mm
Thing is theres no evidence of a leak ANYWHERE , I did change the pipe on the back of the head and thats now dry , every single pipe joint is dry , rad is NEW as are the rad to box pipes - theres just no sign of where its gone .
No smell of antifreeze , no damp inside ( heater matrix ) , EVERYTHING works , car runs at just over 90˚C constant , heater is lovely and hot .
Also No damp that i can see on the engine undertray
SO
Is the top of the divider the actual fill level or is it lower as in where mine is in the photo - am i actually overfilling it or is it leaking ???-
What level do yours run at
Its a 56 C180K .

 

[DexterML]

And so the saga continues ever on
This time the mystery of the coolant dropping with NO apparent leak
Ive been topping it weekly to the top of the divider in the expansion bottle and over a week of shortish runs ( 10 miles per day ) it slowly drops.
Yesterday i checked it as normal and topped it up to the top of the divider - we did 80 miles yesterday in two 40 mile trips and this morning its dropped around 10mm
Thing is theres no evidence of a leak ANYWHERE , I did change the pipe on the back of the head and thats now dry , every single pipe joint is dry , rad is NEW as are the rad to box pipes - theres just no sign of where its gone .
No smell of antifreeze , no damp inside ( heater matrix ) , EVERYTHING works , car runs at just over 90˚C constant , heater is lovely and hot .
Also No damp that i can see on the engine undertray
SO
Is the top of the divider the actual fill level or is it lower as in where mine is in the photo - am i actually overfilling it or is it leaking ???-
What level do yours run at
Its a 56 C180K .

Hello, not MB, but a few years back I had a great 2000 Celica VVTLi which constantly lost coolant with no apparent reason. Eventually we found out that the engine block had cracked. I wholeheartedly hope yours isn't, but if there is no coolant in the engine (gasket issue) then you may want to have a look around just in case you spot something. The coolant will evaporate quickly so it will not be damp if there is a crack somewhere.

 

[johnsco]

Another possible cause is porosity in the engine castings.
It's not something I've ever experienced with any of my MBs.
I always felt that the quality of the castings has been good.
However, it was a common problem in Peugeot 307 engine blocks and was a common cause of head gasket failure and oil in the header tank .
I've just scrapped Mrs J's 307 for just this reason.
My mechanic friend told me it was a common problem with these engines.
He said - Don't bother changing the head gasket, as it will soon fail again.

In the past, I ran three Rover SD1s ... A 2300 straight 6 and then two 3500 V8s.
All lost coolant regularly.
You could never see where it went, but you did need to be checking constantly for it.

I don't usually like adding "stop-leak" additives to the coolant system.
However, if you can't find the leak, it might be an option.

 

[tjc4]

Probably ending up in your wiper fluid. Coolant passes thru wiper fluid to keep it from freezing. Common leak area. See video.

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[Continental]

And so the saga continues ever on
This time the mystery of the coolant dropping with NO apparent leak
Ive been topping it weekly to the top of the divider in the expansion bottle and over a week of shortish runs ( 10 miles per day ) it slowly drops.
Yesterday i checked it as normal and topped it up to the top of the divider - we did 80 miles yesterday in two 40 mile trips and this morning its dropped around 10mm
Thing is theres no evidence of a leak ANYWHERE , I did change the pipe on the back of the head and thats now dry , every single pipe joint is dry , rad is NEW as are the rad to box pipes - theres just no sign of where its gone .
No smell of antifreeze , no damp inside ( heater matrix ) , EVERYTHING works , car runs at just over 90˚C constant , heater is lovely and hot .
Also No damp that i can see on the engine undertray
SO
Is the top of the divider the actual fill level or is it lower as in where mine is in the photo - am i actually overfilling it or is it leaking ???-
What level do yours run at
Its a 56 C180K .

That coolant doesn’t look right at all to me (colour wise and consistency wise from the picture it looks sludge like) I could be completely wrong but might be worth double checking your manual as to what colour it is supposed to be I thought it supposed to be greenish on a w203 c180k but perhaps it can vary or varied after facelift.

 

[Continental]

Another possible cause is porosity in the engine castings.
It's not something I've ever experienced with any of my MBs.
I always felt that the quality of the castings has been good.
However, it was a common problem in Peugeot 307 engine blocks and was a common cause of head gasket failure and oil in the header tank .
I've just scrapped Mrs J's 307 for just this reason.
My mechanic friend told me it was a common problem with these engines.
He said - Don't bother changing the head gasket, as it will soon fail again.

In the past, I ran three Rover SD1s ... A 2300 straight 6 and then two 3500 V8s.
All lost coolant regularly.
You could never see where it went, but you did need to be checking constantly for it.

I don't usually like adding "stop-leak" additives to the coolant system.
However, if you can't find the leak, it might be an option.

Could it be corrosion from the radiator mixing with the coolant?