Coolant Leak - W212 65 reg OM651 engine - Head Gasket?

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Bassmonster

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Aug 1, 2022
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7
Location
ESSEX
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E220, AMG night edition premium OM651, 2015
Hi all,
I'm hoping someone can shed some light on this.

So about 3 weeks ago, my engine coolant sign came up on my dashboard. Not thinking much of it, I filled it up. After driving for about an hour, the next day, i noticed that the coolant sign came back again.
My usual mechanic was very busy so after doing a bit of googling, I decided to find the leak myself by using a Green dye and UV light. However, I found nothing. I then took that car to a garage, he did some kind of pressure test and said that my coolant system was OK and no leaks. He then checked the engine Oil an said it's not totally black like how it should be and said it was runny and said the head gasket has gone. My knowledge is very little when it comes to cars but he said the most common sign of head gasket going is white goo around the engine oil cap but there's no white goo whatsoever. I then took the car to another garage who said he cannot rule out the Head gasket going but not 100% sure.
There's no visible signs of water leaking in the engine but it does seem to be going somewhere.

The last thing I want to do is to spend a of money on getting the head gasket repaired only to find the problem still persists.
Any ideas as what could be causing this issue?
The heater, AC, works just fine and engine not overheating despite losing coolant. However, this is based around 45 minutes of driving or so.
I don't notice any loss of power as such either.

so the coolant loss is maybe around a 1 quarter of a litre after driving around for about 45 minutes or so...
 
Check the water pump for weeping.
Any coolant under the car after parking up?
Also, when up to temperature, look closely at the plastic coolant filling bottle.
Mine had a pinprick hole that wasn't evident until the coolant expanded and squirted out. Couldn't be seen when engine was cold.
 
Hi I had the same problem and it turned out to be the thermostat
 
So, i just went and unscrewed the expansion vessel cap to check the coolant level as I filled it this morning. As soon as i unscrewed, water level started to go down before my eyes and can hear sound when your kitchen sink is partially blocked. I then moved the car to see if there the ground was wet...it wasn't!!!....

@AMGeed and @Retaxus , i'll make those checks and report back later.

@Bigdrew, do you mean there was coolant leaking out from the thermostat?
 
So, i just went and unscrewed the expansion vessel cap to check the coolant level as I filled it this morning. As soon as i unscrewed, water level started to go down before my eyes and can hear sound when your kitchen sink is partially blocked. I then moved the car to see if there the ground was wet...it wasn't!!!....

@AMGeed and @Retaxus , i'll make those checks and report back later.

@Bigdrew, do you mean there was coolant leaking out from the thermostat?
 
Yes bassmonster but I couldn’t see where it was coming from so got a water test
 
Hey all,
I've had another look. I bought one of these pressure testers which works quite well it seems. So I screwed on the pressure tester and increased the pressure to 20 psi. I can see that the pressure started to reduce almost immediately albeit slowly. I checked all the places as mentioned above and was expecting for coolant be squirting out of somewhere but I saw nothing. As I put dye in the coolant, i checked with the UV torch and most prominent place that i can see where there seems to be a leak was at some pipe connected to the EGR cooler. Please see photos. I've also taken photos of other places where there seems to be dye.

It seems that the water is indeed mixing with the oil as when i took out the dipstick, the oil was way above the maximum limit. however, the actual texture of the oil isn't watery enough to explain the amount of coolant being lost.

Another point to note is that when driving and going over humps, i can literally hear like swishy swashy sounds as if it's coming from the dashboard so not sure if the coolant is traveling around the empty parts of the cooling system.

What are those holes where the oil has collected with yellow arrows pointing to them in the above photo as it seems that dye has collected there as well as under UV light it it glows up.

Any advice would be much appreciated.
 

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It sounds like possibly head gasket with water pressure forcing water into a oil gallery, another possibility is if it has a water cooled oil cooler could maybe leak there internally, some of the n55 bmw oil coolers can get this issue due to a seal failure, I'm not sure on whats involved on your cooler but may be worth a check if this could be a feasible issue.
 
Hey all,
So far, i've had 2 garages and a mechanic who works for Mercedes take a look at the car and none of them can categorically state what the issue could be as it's rather unusual as the classic symptoms of mayo underneath the oil cap isn't there. Whatever the issue is, water does seem to be mixing into the engine oil but as to how it's penetrating through seems like a mystery. It seems like a case of getting the head gasket done to see IF the problem gets resolved. I'm not entirely keen on this as it's quite a bit of money and no guarantee of it fixing the problem.

I filled up the coolant about a week ago and didn't drive it at all and was expecting the level to remain the same, however, the tank was almost empty. I initially thought it was only losing coolant whilst driving and vaporizing....

Does anything else have any ideas as to what the issue could be or do i bite the bullet and go head gasket repair?

@KeithDee would you happen to know where the oil cooler is located?

Is there a route through the oil filter/housing that coolant can seep through?
 
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This shows oil leaking into the coolant but I cant see any reason why it couldn't be the other way around with coolant leaking into the oil, maybe the cheaper option to get checked out.

Keith
 

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