Coolant Leak Source W212 E250 OM651 ?

[pmcgsmurf]

Not driven much this one, about 33k miles, driven about twice as much as other one on 17k miles.

Might try some UV dye first just in case it's doing it when being driven hard.
Anyone recommend a UV dye?

If we can't find it with this it's strip down time.

 

[zipdip]

Screwfix do a engine UV dye a mate used it last year to trace a coolant leak.

 

[Justintyme]

Hi folks

I'm guessing this is coming from the Fuel Filter housing, anyone any thoughts?View attachment 75312
Picture is looking up from underneath and we can see signs of coolant coming from above onto the little silver bracket.
No sign of any leak at the water pump.

Hi pmcgsmurf, I have a very small coolant leak in my w212 Om 651 200 CD1. I cant see it leaking anywhere, even though I have put UV leak finder into the water. So now the fuel filter housing is under scrutiny...I have attached a pic, taken from the top, with arrows showing the position of the hoses , and so far nothing showing at this location. Is it even possible to see the location where it would be leaking from where the pic was taken? Or is only visible from underneath, with the mud shields removed. From looking at your pics, It's starting to become a bit clearer to me.. in your 3rd pic ( showing the part with the 3 holes ) That's the actual heated fuel filter housing? and where these 2 (3) holes are located, is where it bolts to the head, and that's where it normally leaks? And this means a replacement of the complete unit, or will a gasket do the job? Seems like a bit of a pig of a job … did you have many problems with it? Was it leaking so badly that you had to replace it? Aside from the inconvenience of continually topping up the reservoir, was it doing other damage too? Other than maybe staining your drive way? Sorry for the long winded questionnaire, but grateful for any help you can give.

 

[Justintyme]

I just lost all my coolant last night. Checked it today with some die. Its coming out the "freeze plug" which is screwed into the engine as far as I can see. Still trying to source the part. Nobody seems to know anything about them or replacing them. Hopefully thats all your problem is, just a wee gasket or something on one of the parts AND NOT THE HEAD GASGET lol

Only thing good you can say about this kind of a leak HITECK, is that it can't be too difficult to trace, 8 ltrs of liquid cannot just vanish ( much as it may seem like it,,,,,) Good Luck with it, I hope that you will find a quick easy fix...

 

[Justintyme]

I just lost all my coolant last night. Checked it today with some die. Its coming out the "freeze plug" which is screwed into the engine as far as I can see. Still trying to source the part. Nobody seems to know anything about them or replacing them. Hopefully thats all your problem is, just a wee gasket or something on one of the parts AND NOT THE HEAD GASGET lol

Freeze plug.....been years since I even heard of them. Once upon a time though, they were a common cause of cars being off the road, and in the garage. Winter was their favourite time. I thought technology had eliminated them, seems like they are still part and parcel of modern engines though, just I have not had any experience with them in a long time.

 

[pmcgsmurf]

Hi pmcgsmurf, I have a very small coolant leak in my w212 Om 651 200 CD1. I cant see it leaking anywhere, even though I have put UV leak finder into the water. So now the fuel filter housing is under scrutiny...I have attached a pic, taken from the top, wiith arrows showing the position of the hoses , and so far nothing showing at this location. Is it even possible to see the location where it would be leaking from where the pic was taken?
Or is only visible from underneath, with the mud shields removed.

We could not really see the leak.

From looking at your pics, It's starting to become a bit clearer to me.. in your 3rd pic ( showing the part with the 3 holes ) That's the actual heated fuel filter housing? and where these 2 (3) holes are located, is where it bolts to the head, and that's where it normally leaks?

Yes, that's correct.

And this means a replacement of the complete unit, or will a gasket do the job? Seems like a bit of a pig of a job … did you have many problems with it?

To most it would be crazy to strip this all down then try and save a few pounds doing the repair on the cheap.
The replacement part is new/improved to absolutely makes sense to replace it since the entire thing is stripped down.

Was it leaking so badly that you had to replace it? Aside from the inconvenience of continually topping up the reservoir, was it doing other damage too? Other than maybe staining your drive way? Sorry for the long winded questionnaire, but grateful for any help you can give.

Did we have to, not really but then there is lots of things we don't have to do to our cars.
The leak was/is a nuisance having to top up all the time, likely not doing any damage as long as the car is kept topped up.

This one is still losing fluid so next up will be the water pump.

 

[Justintyme]

Hi again pmcgsmurf, That was a fine quick and detailed reply !!! Thank you!
While I have experience of working with outer makes, this is my 1st Mercedes, and I learned a long time ago ( the hard way )to ask first, before blindly ploughing ahead with an unknown job !!! Up to the time yesterday evening when I saw your post, that was my first time actually seeing what the fuel filter housing looked like !!! I was literally poking around in the dark. I have been searching the net and forums, since I first noticed the leak, to try and get a pic or diagram ( even in parts catalogues) No luck until your post. Thanks again for that !!! ( maybe you can suggest a w212 parts catalogue, as I will need to order one? )Now not only do I know what it looks like, I know where it goes !!!
Next thing is a visit to my friend with the lift and check it out from underneath. Well and good if I can see a leak with the UV light, then that question will have been solved ( assuming only 1 leak ) and hopefully, the water is not finding itself into the ATF fluid in the transmission ( a frequent occurrence in older Mercs ( pre 212 ) as far as I have heard, or even worse, indicating a faulty head gasket. Then of course, as in your case, it could still be the water pump. When the car is driving, the pump leaks minute amounts of coolant, which is quickly blown away, leaving no visible trace. Not even UV.
Of course if I find that it is the coolant part you replaced, I will replace it too. I was just wondering that with about 95 % of parts with mating surfaces, there is a gasket of some kind, what was the set up with this fitting. You were right to replace it. Its too much work to go to and NOT replace it. Normally I would be pre-emptive when it comes to parts needing replacement, tyres, brakes servicing etc. would all be done on time ( if not before) and this is easy as it would be pre-planned. But in a case like this where you know you have a problem, but can't quite pin point the cause. That's a right pain !!! Hence my question about " Topping -up and Driving On" despite it being a pain and a nuisance ( even more so, if you are very particular about your Merc, as I am pretty sure you are)
I hope that you pinpoint the cause of your leak pmcgsmurf, and fix it. Let us know how you are getting on. While I know that its a problem for you, It was (and is) a great post, and I'm sure that it will be a help to many,. I hope that is some consolation to you.
Thanks again, and "Good Luck "
Justintyme.

 

[Justintyme]

Im assuming any you have replaced yourself have all been plugged in. For your information IT IS ACTUALLY internally threaded on some engines and screwed into the block as it is in mine. The purpose of them has absolutely nothing to do with being a valve to release pressure. They were put in during the molding of the engines to withdraw any excess sand/washing down after the molding. I have looked into it and used my own qualifications in metallurgy & inspection to understand the point of them. They were given the name freeze plugs by usa / uk ? I have no idea. But yes you are right one technical term for them could be a core plug. Check your books or Autodata and you will see. The replacement I have is also internally threaded to screw into the block with the seal inside it. Thanks for the info anyway but the problem now is replacing it without removing the dpf or exhaust. Its in an extremely awkward place to get to. I reckon I might just reach it with a wobble on an extension. Any info or advice on the access to it would be appreciated.

That's very interesting HITECH, I remember replacing frost / core plug's many years ago and the teaching then was that they were designed to go rather than damage the block. And in truth, it seemed that they did seem to go more in winter than in summer !!! So maybe that was not their designed function, but coincidental? I remember fitting them in Ford 100'e engines, ( which was not exactly yesterday or the day before... ) and they were a regular sight in the workshop. But regardless of function, design etc. They can be a right pain in the butt when the leak, especially in modern engines where nearly everything is difficult to get at. Thanks for the "Heads Up" on it. I would say that the majority of mechanics out there do not know that.

 

[HITECH]

Got it changed in the end. Was a slow and painstaking process requiring lots of patience, heat, cups of tea and positive thinking. Probably woudnt have been so difficult to get it out if it had not been threaded.

That's very interesting HITECH, I remember replacing frost / core plug's many years ago and the teaching then was that they were designed to go rather than damage the block. And in truth, it seemed that they did seem to go more in winter than in summer !!! So maybe that was not their designed function, but coincidental? I remember fitting them in Ford 100'e engines, ( which was not exactly yesterday or the day before... ) and they were a regular sight in the workshop. But regardless of function, design etc. They can be a right pain in the butt when the leak, especially in modern engines where nearly everything is difficult to get at. Thanks for the "Heads Up" on it. I would say that the majority of mechanics out there do not know that.

 

[Deleted member 126969]

I always knew them to be called 'core plugs', as in casting core...for the reason mentioned. That they acted as a pressure release in the event of frozen coolant was mostly serendipitous I think. The usual function of a pressed steel core plug was to rot out when you least expected it.... Hardly surprising that they invariably rotted at the 'corner, where the metal was thinnest and had frozen in strain from the forming process, as well as the fact that any plating or finish would have been removed when it was pressed into the casting.

I recall changing quite a few as a lad - nearly always at the back of the block, meaning engine or gearbox out, flywheel off etc.

Also, I don't recall seeing anything other than a threaded plug in an alloy casting though, except perhaps a small steel on in the old Rover V8 that went into the main oil return gallery in the top of the V??? (might be imagining that one). A plain steel 'core plug' in an alloy casting probably wouldn't stay seal very long with the very different expansion rates?

 

[Justintyme]

Got some time today so stripped this down, what a real pain in the backside.

You have to first remove the Vacuum Sensor, then remove the Exhaust Gas Recirculation Cooler.
With these out you then have access to remove the Fuel Filter Housing (with some bendy sockets).

Engine bay looks like this now till after lunch at least.
View attachment 76211

The old filter housing looked like this., note the 2 holes to bolt this on.
View attachment 76212

New one looks like this, 3 holes although we can only use 2.
Thought we had a wrong part at first but guess they have just improved so it does not leak.
View attachment 76213

Hi Patrick, quick question for you. When you remove the fuel filter from the housing, is it possible at that point to see if the housing is leaking at the block?
Thanks. Justintyme,
PS: have you managed to sort out the leak by now?

 

[pmcgsmurf]

Hi Patrick, quick question for you. When you remove the fuel filter from the housing, is it possible at that point to see if the housing is leaking at the block?

Not as far as I know.

PS: have you managed to sort out the leak by now?

No, not had any time lately.

 

[Smudge2137]

Did you find out what the issue was in the end ?

 

[HITECH]

Yeah I had to change mine last year. Was a pig to get access to but absolutely no way did I need to remove the gearbox or engine. Everything else below above and around it yeh. Dpf, turbo hoses, pipes, wiring loom amongst other things. Mine was right at the back aswell on the bottom. It was also screwed in. Most people in this forum were arguing it defo wouldnt be a screw in type but it was. It had well corroded due to a previous owners neglect no doubt. There was nothing left of it to actually get any kind of tools onto it to unscrew and remove it. It needed heat on it and various tools to cut it all out without damaging the block and inner thread. The important thing being not to damage the thread. Had started as a slow leak and was troublesome to find out where the coolant was leaking from. As soon as I stuck some die in the water it was very obvious to find and would only leak when the car got up to temp and the thermostat opened. Your comment :
A plain steel 'core plug' in an alloy casting probably wouldn't stay seal very long with the very different expansion rates?

Your bang on there m8. I completely agree ! The majority of them core plugs will be screw type.

I always knew them to be called 'core plugs', as in casting core...for the reason mentioned. That they acted as a pressure release in the event of frozen coolant was mostly serendipitous I think. The usual function of a pressed steel core plug was to rot out when you least expected it.... Hardly surprising that they invariably rotted at the 'corner, where the metal was thinnest and had frozen in strain from the forming process, as well as the fact that any plating or finish would have been removed when it was pressed into the casting. Your comment :
A plain steel 'core plug' in an alloy casting probably wouldn't stay seal very long with the very different expansion rates?

I recall changing quite a few as a lad - nearly always at the back of the block, meaning engine or gearbox out, flywheel off etc.

Your bang on there m8. Icompletely agree !

Also, I don't recall seeing anything other than a threaded plug in an alloy casting though, except perhaps a small steel on in the old Rover V8 that went into the main oil return gallery in the top of the V??? (might be imagining that one). A plain steel 'core plug' in an alloy casting probably wouldn't stay seal very long with the very different expansion rates?

 

[pmcgsmurf]

This one still has a very small leak so today we have changed the old water pump A6512001901 for the very latest one A6512007701.

Old pump was plastic housing and new one is metal.

Will see how it goes with this.

 

[MercedesDriver]

I’m now on my second A6512007701 in 9 months. The first one started to leak after 6 months and got it changed within a warranty in July.
Have you checked oil cooler? In May my oil cooler started to leak so got it changed in June.

 

[pmcgsmurf]

I’m now on my second A6512007701 in 9 months. The first one started to leak after 6 months and got it changed within a warranty in July.
Have you checked oil cooler? In May my oil cooler started to leak so got it changed in June.

Hope we have better luck with this one, we checked the cooler when we did the fuel filter housing and seemed ok.

 

[pmcgsmurf]

Message on dash, top up fluid.............ARGH..........................

 

[MercedesDriver]

Just a thought.
Are there any water marks on the top of the expansion reservoir? I have changed the reservoir cap and since then it's nice and clean. Part no is MA2105010615, £19.80 from MB

 

[pmcgsmurf]

Are there any water marks on the top of the expansion reservoir? I have changed the reservoir cap and since then it's nice and clean. Part no is MA2105010615, £19.80 from MB

Not noticed any, double checked today and swapped the cap from the other car so will know soon enough if there is a problem if the other car loses fluid.