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Old Apr 20, 2022 | 11:24 AM
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E class w212
Overfilled coolant

So today i wanted to add some coolant in the reservoir and i overfilled it by mistake, will it cause any problems ?
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Old Apr 20, 2022 | 11:55 AM
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2011 E550 | M273 | 4Matic NA | W212
How much did you overfill? Can you go to a hardware or pharmacy store, find a syringe or pipette, turkey baster, ect, and remove the excess coolant? These items are long enough and the coolant close enough to the top to do.
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Old Apr 20, 2022 | 02:52 PM
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W212 MY'14 M276-3.5NA @75kMi
extreme pressures...

You know how liquid and gas expends when heated, right?

When the expansion tank has no room, extreme pressure gets placed on the closed circuit weak points: head-gaskets, O-rings, hoses, pump seal...

Get your coolant level below MAX soon.
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Old Apr 21, 2022 | 12:29 AM
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Umm...
You know the pressure caps are also pressure relief caps, right? The worst that will happen with an overfilled system is some fluid getting burped onto the ground. Not altogether ideal, given it is toxic to things with heartbeats, but I'd hardly lose any sleep over it.

That said, it is easy to pull out a couple of cups of coolant to correct the overfill.
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Old Apr 21, 2022 | 12:55 AM
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Originally Posted by Noureddinee
So today i wanted to add some coolant in the reservoir and i overfilled it by mistake, will it cause any problems ?
Like rapidoxidation already said, don't lose any sleep over it. You can overfill the coolant as much as you can fit in the reservoir and it will do no harm. When the fluid expands too much to fit in the system the pressure valve built in the reservoir cap will let the fluid out in the ground. No harm to your engine is done with this as all of the other seal points are built for much higher pressure than the reservoir cap.
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Old Apr 21, 2022 | 03:17 AM
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W212 MY'14 M276-3.5NA @75kMi
coolant closed circuit...

Originally Posted by Noureddinee
So today i wanted to add some coolant in the reservoir and i overfilled it by mistake, will it cause any problems ?
Have you figured out where the engine coolant is leaking from?

I am not convinced these engines are immune to high pressure damages... one example is the engine oil heat exchanger busting its seal.

Last edited by CaliBenzDriver; Apr 21, 2022 at 03:59 AM.
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Old Apr 21, 2022 | 08:13 AM
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E class w212
Originally Posted by rapidoxidation
Umm...
You know the pressure caps are also pressure relief caps, right? The worst that will happen with an overfilled system is some fluid getting burped onto the ground. Not altogether ideal, given it is toxic to things with heartbeats, but I'd hardly lose any sleep over it.

That said, it is easy to pull out a couple of cups of coolant to correct the overfill.
that is exactly what happened now coolant level went back to the normal level
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Old Apr 21, 2022 | 08:14 AM
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Originally Posted by Arrie
Like rapidoxidation already said, don't lose any sleep over it. You can overfill the coolant as much as you can fit in the reservoir and it will do no harm. When the fluid expands too much to fit in the system the pressure valve built in the reservoir cap will let the fluid out in the ground. No harm to your engine is done with this as all of the other seal points are built for much higher pressure than the reservoir cap.
thanks for the clear explanation
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Old Apr 21, 2022 | 08:20 AM
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E class w212
Originally Posted by CaliBenzDriver
Have you figured out where the engine coolant is leaking from?

I am not convinced these engines are immune to high pressure damages... one example is the engine oil heat exchanger busting its seal.
there’s no leaking , i have recently changed the whole coolant system, and redone the headgasket
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Old Apr 21, 2022 | 09:58 AM
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You can't overfill MB coolant system. It has the fill neck design for air bubble, just like gas cans.
Worse can happen is when you top it off on cold engine, the bubble might become too small.
I always top off coolant on warm engine and that makes perfect level.
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Old Apr 21, 2022 | 10:12 AM
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Originally Posted by kajtek1
You can't overfill MB coolant system. It has the fill neck design for air bubble, just like gas cans.
Worse can happen is when you top it off on cold engine, the bubble might become too small.
I always top off coolant on warm engine and that makes perfect level.
engine was warm 😄
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Old Apr 21, 2022 | 11:23 AM
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Level indicators exist for a reason. Fill fluids to proper volume.
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Old Oct 21, 2022 | 03:54 PM
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Originally Posted by CaliBenzDriver
You know how liquid and gas expends when heated, right?

When the expansion tank has no room, extreme pressure gets placed on the closed circuit weak points: head-gaskets, O-rings, hoses, pump seal...

Get your coolant level below MAX soon.
I’m sorta agreeing with you especially when it comes to older cars. I too overfilled my expansion tank 2013 e550. Theoretically it should have purged itself and the passenger side of the bottom plastic splash pan should be dripped with coolant right? Well the driver side is the side that’s dripped with coolant. The pressure pushed out the coolant on that side. Will have to do a coolant pressure test to see where it’s leaking, but I jacked up the car and let it idle for 20 minutes and revved up the engine and I don’t see any leaks. Hopefully it purged itself and that’s the end of it but you can never be to careful, especially in this situation.
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Old Oct 22, 2022 | 06:51 AM
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Originally Posted by CaliBenzDriver
You know how liquid and gas expends when heated, right?

When the expansion tank has no room, extreme pressure gets placed on the closed circuit weak points: head-gaskets, O-rings, hoses, pump seal...

Get your coolant level below MAX soon.
huh?
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Old Oct 22, 2022 | 11:47 AM
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2014 - W212.065 - E400 ( M276.820, 3 liter Turbo) RWD not Hybrid
DO NOT overfill your expansion tank, it is indeed bad for cooling system pressure wise.

Air is compressible, liquid is not. Yes, it has the pressure cap but that is a 1.4BAR rating or 20 psi.

50/50 coolant has expansion of approx 6% and commonly expansion tank is 12% of coolant capacity.
Our reservoir is approx 1ish liter and the air space when properly filled ( HALF ) is about 0.5 to 0.6 liters, which correspond to half of 12% of 9-10 liters of coolant.

Our coolant circulation pump or the cooling system overall pressure even at 108C / 226F temperature is only 11 or so PSI at 4,200RPM. Probably at WOT redline it may do 13 PSI at best.




So by having air space for coolant expansion, we have some buffer for pressure increase on the compressible air-space and that is good for plastics.
If all liquid due to an overfilled condition..... sure the pressure cap will allow release but that is pressure torture at 20 psi... pity the cooling system.














Source : https://www.dewitts.com/blogs/news/1...g-should-i-use




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Old Oct 22, 2022 | 02:36 PM
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coolant pressure tank

thank you Surya for the perfect explanation of necessary air volume.

pressure to temp relationship

When the plastic cap starts leaking pressure, the boil over temp drops towards 226°F.

Last edited by CaliBenzDriver; Oct 22, 2022 at 02:52 PM.
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Old Oct 23, 2022 | 07:10 AM
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the cap will let it blow of some STEAM, air and/or liquid.
IT is a relief valve for coolant system.

Reason for air space in bottle is to keep it from over-flowing as fluid expands when heated and keeping garage floor nice and clean.

IF it leaked out excess on to floor, owners would be bringing cars back in all the time for warranty;
so fix was external tank with Hot Min/Max lines halfway up.

Before this all they had was cap on radiator and drain hose down the side to near ground - Think 70's

When it dumps air = no mess.
When it dumps over-filled coolant = mess out of that hose which snakes to near ground near cap.

Just wait for it to cool and get OLD turkey baster and take some out.
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