Mystery oil leak on glk250 (om651 engine)
 

Hello, would anyone happen to know where the line at the back of the om651 engine leads to? And why it would be leaking oil? I’m thinking possibly a drain for the valve galley in the center of the valve cover where the injectors go, or maybe a tattle tale from the cylinder heads or over flow from the engine block/ oil pan..




I’ve ordered a valve cover gasket but I’m hoping someone could shed some light before I start disassembly. I’ll attach photos of the hose in question it’s routed down the drivers side of the engine and is tethered to the side of the bellhousing. It is #240 in the diagram. Thanks -Ryan


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Ok, I think I’ve got it figured my guess is this hose is a secondary crankcase vent (to atmosphere) as a fail safe should the primary crankcase breather become plugged in order to avoid excessive crank case pressure which would throw codes and probally blow out seals/be hard on components. I’m going to clean/replace pcv system when I get around to it and see if this remedy’s the leak. I will post photos and results should anyone else ever have this problem.

Subscribed. Good luck and post back!

And what did you find out?

Filippo

Check Oil Pan
 

So I rerouted PCV to a catch can with a breather, but as it turns out my oil leak was coming from the oil pan between the transmission bellhousing and motor. The fix requires removing cvs, and motor mounts...MAJOR PITA! Mercedes does not use a molded gasket Just a Mercedes RTV that they squirt on before assembly, Really Piss poor design in my opinion as the oil level when in the full range sits above level of RTV sealant. So oil continues leaking out pan Even while The engine is off, until it drains to low mark on dip stick than stops dripping. Let’s hope whoever did the assembly was just being conservative on this one with the Silicone.

Ryan, thanks for the reply. Ouch. There is precious little information on these vehicles. I do most of the work myself, and mostly BMW (one diesel) which I've very familiar with.

I'm at 80k miles and have done charge pipe (split), usual filters on time. These cars are well put together in my experience. I've done a full trans fluid change (pressurized), changed a few other small items, like soot particulate sensor. It needs dampers, which I'd do with Bilstein OE at some point.

I'm not very Mercedes familiar. I suspect same candidate companies for various parts, as BMW. At 80-100k or so, what should I be considering? Serpentine and pulley/tensioner? Valve cover gasket? What's extent of PCV system (I find no one online discussing)? Anything else I'm missing? Does the EGR valve get cleaned out?

Thanks!

Filippo

Good diagnosing and repair work, as oil is the lifeblood of this beast. I'm at 122K miles and no oil drips that I can see. The next job on the list is v-belt and pulleys with tensioner (still on originals).

@fmorelli, if you don't have leaks then don't worry about gaskets yet. As for EGR valve, it can be cleaned but it's quite a PITA to get to, underneath the plastic intake manifold. My advice is to drive it in a spirited fashion, as turbodiesels love to be on boost. If you really want to clean the EGR valve, then taking off the plastic intake manifold and cleaning that as well makes more sense. Although with today's ULSD fuel, EGR and intake clogging should be a thing of the past....Once both are clean, I would look for a software solution to deactivate EGR as much as possible. Zero is ideal in my book; less abrasive soot compounds that don't get into the oil and end scratching the inside of your cylinder liners. It's quite remarkable the difference in visual oil quality pre- and post-tuning.

Also, since you've done the transmission flush, what about the rear diff fluid?

@andreigbs thanks for the comments. I've not done the rear diff. Didn't really figure that was a big issue since those are synthetics and reasonably sealed?

Hard part with these vehicles is there is just not much chatter. I'm used to BMW resources too which are more robust, including retail support network. You should see the harangue I went through Bosch USA and with FCPEuro to get a soot particulate sensor. I won't bore you. Amazing the folks that makes parts for these cars - Ina, Febi, Gates, Contitech, Graf, Rein, CRP, et al ... yet not so easy to find. One-stop shopping seems difficult. Even doing rope-a-dope with Mercedes EPC can be a challenge ... half dozen coolant pump superceisions?! lol

I had some oil inside the bottom of the driver-side charge pipe. My vote is oil condensate converting to fluid at a low point. This thing runs like a champ.

But when I did the driver-side charge pipe last week, I noticed oil on the driver side of the motor. Could be from oil filter assembly.

So from your comments, sounds like the accessory drive assembly pretty stout. Water pump/Thermostat? Can I wait a while at 80k? I'm not looking to do maintenance for maintenance sake - I have enough backlog on car work as it is. Just looking for practical advise at 80k miles on the GLK250.

Thanks!

Filippo

I think a little bit of oily residue is normal and to be expected in intercooler pipes; I've seen it in both gas and diesel turbo engines with no ill effects. A lot of oil inside would be indicative of weak turbo seals or other issues. It would be ideal to have no oil leaks obviously, so if you can pinpoint where the leak is or whether it's just some oil seepage/sweating with time that'd be my first step. The rear diff fluid is indeed synthetic, but I don't believe in "lifetime fluids" no matter what. I apply the same rule to my X3d which ZF says has lifetime transmission fluid; it has 57k miles on it now and will get its first transmission flush right around 60k miles.

The belt, pulleys and tensioner has proven to be reliable, I would plan on doing them starting with 120k miles and definitely before 130k. If a second set gets you to 200k+ miles safely, it's just good sense to do it no later than 120-130k. Same thing with the water pump, which is plastic and has a plastic impeller I believe. There is definitely an upgraded pump which is all metal, so that's the one to get. The thermostat is electric and should be replaced if it's (a) giving you issues already, or (b) you're replacing the water pump too. Same principle: if the originals get you safely to 120-130k miles, a second set should easily last past 200k miles.

This is, of course, assuming you plan to keep your Bluetec for as long as financially feasible. The weak points on our diesel GLKs is the exhaust aftertreatment system. Everything else is nuts and bolts that can be replaced and are engineered to be robust.

Thanks for tips on long term maintenance.