I find once a year that I need to top off the coolant tank on my E63S. I've seen no leaks or seepage so I wonder if this is just a bit of evaporation or pressure release. Anyone else experience this?

 

I have also done the same by adding a bit over the past 5 yrs. I don't believe this is a concern.

 

just the other day the coolant light came on on mine the first time ever, right after coming back from a shop for a different issue (one thinks they'd have paid attention to a low level) . . . However, I have never noticed any indication of a leak of any sort so I just figured its just normal consumption, not any reason for concern. I'm @ 55,000 ish

 

coolant supposed to be closed system ie never gain nor lose any.
Only way could lose in proper system is Pressure gets too high and cap vents some steam which will have some liquid in it.
This would take a lot of time to lose a pint or so of liquid in steam form.

May I suggest a pressure test of system and Importantly pressure test cap.
You pump up to pressure of cap on car and see if it holds for couple of hours.
FOr cap you pump up to check relief pressure is OK and then let it shut and hold a pressure for coupe of hours.

If all OK then my guess is system generates too much pressure and you vent it as steam.
Signs would be greasy messy around pressure cap from steam venting.
Coolant pressure sensor would let you know this but alas never seen that done.



Or worse case small cracks in block, head or head gasket and coolant is burned off in combustion.
Can pass compression tests here unless engine is HOT when testing.

 

My 2021 has 9400 miles on it. Have not had to add any coolant, and no lights/warnings so far.

 

Check the level on the coolant tank. You won't get a warning until it is below the Min mark

 

Whether it was coincidence or not, I had the low coolant warning come on at around 27K miles, a few days after a track day in mid-October 2021. This was a wet day on a short track (Driver Development Track at Canadian Tire Motorsports Park), so speeds were not terribly high and neither was the stress on the engine. The engine certainly did not overheat during the session. Unfortunately I never checked/worried about the coolant prior to the light coming on.

I'm still under warranty, so I took it to the dealer. They pressure tested the system, reported "no fault found" and topped up the coolant. I'm now at 35K miles, and (now that I'm checking regularly...) I haven't seen any further loss of coolant.

Ivan MacKenzie.

 

The tank is full also.

 

If you track it is possible the thermostat can get stress cracks from high heat than normal or leak from the oring at the water pump connection to the thermostat. also these cars are know for faulty reading at the sensor in the resivor or the turbo coolant connection as well I’ve experienced low coolant twice on my c450 twice years ago one nothing since but did happen when I’d drive it really hard so it’s possible it’s lost into vapor. And mine did it after all the bolt ons and flash so if your over stock boost that’s possible to use up some coolant it happened to me.

 

I think it's normal if you don't see any leaks under your drive way. This happened to me as well and after top up no issues at all. AMG engine runs pretty hot so maybe that is the cause of it.

 

I had this too. Had to top up at 50k miles. System checked and was fine.