So I just inherited my parents' old 2009 W164 ML320 Bluetec and noticed some odd things. The vehicle has around 160k km on it.

1) There was an oil leak that probably began in 2014 or 2016, around that period. I don't remember the exact year but I do know it was when the ELW had already ended and their service advisor just said ignore it's not worth replacing the seals (which I agree). However, the leak stopped in about 2019 and the garage floor is completely dry with no stains.

2) The oil consumption is excessive (which seems to be the norm of OM642 engines) but the check engine oil level notification comes on every 1200-1300km or so. However, each time, the amount of oil top up required varies from 1.5 to 3.5L, is this the norm of these arounds of this age and mileage? Also, is the differing amount required for top up each time an indication that the oil level sensor is faulty?

Some things to note is that the vehicle essentially saw very little mileage from mid 2015 to 2020, probably around 8000km annually mostly as a beater for errands at that point. In the latter part of its life, it was driven much harder and at higher speeds 140km/h than before. The turbo was replaced and DPF cleaned end of last year.


Is there any reason as to why the oil leak stopped even though the dealer back then said it was from the oil cooler? Given it's an 09 and first year of the facelift, it most probably has the old seal type. Indy shop said they cant find a leak at the turbo or oil pan and suggested replacing the PCV valve but mentioned that it's not a guarantee and just a trial and error at this point. MB said the oil consumption is from the oil leak without looking again. Also, is the oil consumption normal with the age and mileage of the vehicle? Does running at higher speeds also burn more oil?

Also, on the newer OM642 engines like my W166 GLE, should it be expected to have high engine oil consumption later down the road or it's only a characteristic of the first gen Bluetec's?


I don't mind spending normal or even additional maintenance on it or topping up oil every once in a while which does get bothersome sometimes but I guess I need to figure out where to draw the line since 7k was spent to replace the turbo and clean the DPF when the dealer was offering 1650 for it on a trade in at the time (the tires cost more). Parents wanted to get rid of this back in 2014 when they replaced the suv (twice now) but I insisted on keeping it given its sentimental value as it was the vehicle where I learned how to drive. I guess at this point, I just want to figure how much is too much when servicing this vehicle as I still want to keep it but just need to figure out what's considered reasonable or logical? Is it just a fact which I should accept as is and live with it as a compromise since I decided to keep such an old vehicle?

 

I don't have any real answers for you, but...

I'd start checking the oil level with the dip stick, at least every time you fuel up. Being down 3.5L is not a good thing. First, try to establish a pattern. Try checking it after you drive it, and again before you drive it the next time. I'm wondering if maybe the oil isn't draining back to the pan consistently. Or, different driving patterns can lead to radically different consumption rates. I knew of a car that would use a quart every 200 miles on the highway but nothing significant in town.

Don't rely on the check oil light. One failure and you're looking at a new engine.

That's a good one. Usually it means you're out of oil!

 

Will do, thanks. It's just been used for misc errands that require longer, highway drives and just want to use a beater for those tasks, just max 150-200km at a time. However, it's mostly being driven at 120-140km/h and with the 7g tronic, it mostly holds it in 2000-2100rpm at those speeds. Since it's essentially running constantly at such rpms, does that burn more engine oil than low rpm, city driving?


I don't think so because it just stopped dripping after that year and hasn't dripped since even after when topped up. Dipstick has never shown it to be completely dry so it's really odd as to why it stopped and hasn't dripped since.

Would there be any other reason as to why it stopped or would MB have misdiagnosed it in the very beginning since it doesn't really make sense for them to disassemble the engine to see if it's the oil cooler leaking? Do they normally just say assume it's the oil cooler if they see drips on the OM642?

Finally, is this also something I should expect on the W166 to eventually happen with age?

 

2008 ML320 has this oil cooler leak, randomly increases and decreases (even stopped for several weeks at one point) - after doing a bit of research have decided to try ATP AT-205 Seal Leak Stopper to see if that stops it. Vehicle is 15 years old, 195k miles runs perfectly but it costs $8k+ to fix. Will report back if this helps.

 

1st start recording oil addition to have solid evidence as human memory is very lousy tool.
There was a member with sedan, who complained about oil usage for years and having extended warranty took the car to dealer several times. Dealer started to monitor oil additions and surprisingly MB allows for quite big oil usage, even most of us have engine who needs no addition between the changes.
So after years of tracking the issue, the mechanic found small drip on the engine in hard to see area and after fixing, the oil usage stop.
So just becouse you don't see oil on the floor, doesn't mean you don't have a leak. Small drips will stop on belly pans and evaporate during drive.
I used to drive 2007 E320 BT with this engine and now have it in Sprinter. None of them uses oil, although I drove only 4000 miles in Sprinter, so don't have long-term experience.
I always keep my engines clean, what helps pinpoint the problem.
Had low boost code popping on my Sprinter twice last year and oily marks on intercooler hose clearly indicate failed seal. Replaced the seal and no more codes.
So if you keep it clean and keep checking, you will find it.

 

Noted thanks for the info.

I just found it odd because when the vehicle had the leak (which lasted for a couple of years), it would be a pretty obvious and large leak on the garage floor, probably 2-4 inches in diameter after each drive and then it just stopped. It's was obvious because after building a new place where the garage floor is completely stain free, there hasnt been a single oil drip and I would say the vehicle is being used to the same amount as back when the leak occurred.

But generally speaking, what would cause what I would assume to be a decently large oil leak to cease and just stop or become a minute leak that's not dripping out?

Shop said that with the mileage, top ups every 1300km arent unheard of and can try replacing the PCV valve at next service interval. I do want to keep the vehicle as it's more of a sentimental item at this point and it still runs and drives fine; is it worth throwing in an additional couple k to try to pinpoint the issue or just let it be?