hey everyone, just wanted to put up a post regarding ownership of the m278 long term, regarding reliability, maintenance and issues over the years.

my personal experience has been better than great, couldn't be happier with how the vehicle has performed over the year's.

i have seen many post's of spooky stories about m278 issue's including but not limited too cylinder scoring, oil pump failure, seized engines in general as well as many smaller items (timing chains, phaser failure, guides etc)

just wanted too put up a post for those of which are looking too see what 13 years of ownership consisted of personally for myself and a list of parts replaced along with maintenance schedules

the vehicle i am introducing is my 2012 ML550, i will be including some photo's and video's later this week

currently at 170,000 miles

I had the vehicle tuned by a local shop (ECUtuninggroup) since 32,000 miles

the tune is advertised at 510hp -680ft/lbs

had it dyno'd in 2019 with 103,000 miles

462 hp 564ft/lbs

always ran on 91octane from shell

differentials are original with the car
transmission is original
water pump and cooling system is original
AC is original (still blows cold)
engine is original

here's a detailed list of maintenance and then i will get into failures and repairs

oil changes every 6000miles
Pennzoil 0w20 w MANN filter's

spark plugs every 25,000miles
NGK 97506 (one step colder then factory) gapped at .7MM

722.9 7G Tronic transmission
serviced every 55,000 miles
FUCH's Titan 4134 ATF + Merc filter

differential oil's changed every 55,000Miles
Liqui moly 75w90

transfer case oil every 55,000Miles
Chrysler ATF+4

i believe that cover's most of the maintenance

here is a list of parts over the ownership of the vehicle including engine

transfer case failure @ 74,000miles
originally i assumed the issue i was having (slight clunk and almost hesitation from a stop)
was a stretched transfer case chain. So i ordered the replacement and installed HYVO 420 chain.

this only improved said hesitation 50% and i ended up having the planetary housing of the transfer case develop a hairline crack within 5000 miles of new chain.
i only found crack when i noticed smoke coming from back of suv while driving.

ended up replacing the entire transfer case for a new reman transfer case with a 3 year warranty. ($1350) I installed.

air bags in rear of car began leaking at 90,000miles
i replaced them ($840)

front+rear rotor's and pads every 40,000Miles
(cant recall price but in the neighborhood of $1000 each time)

on it's third set of ball joints.

first set of cv shafts front and rear at 160,000Miles
(no failure but the boot's were torn, so i decided to replace them with oem)
($800 for all 4 corner's)

Engine issue's

I have replaced all 4 cam sensor's 3 times due to Wicking and check engine light
(oil can climb up wiring harness and damage ecu and or other sensor's tied into the harness)
I have not ran the aftermarket pigtails, just replaced all 4 sensor's every 55,000 Miles

coolant hose (upper and lower @125,000 miles)

coil packs (first full set @75,000miles)
its second set (@140,000miles) replaced due to miss fire's,

I recently had a miss fire on cylinder 4 so i decided to take all 8 injector's out for cleaning
as well as bore scoping to check for cylinder wall wear. will include pics later this week of every cylinder

i will include some photo's of what to expect regarding the condition of your injector's once you get up in mileage
[img alt="cylinder 4 ohm reading
"]https://cimg1.ibsrv.net/gimg/www.mbworld.org-vbulletin/2000x1124/20251214_161534_2__20f39f1f9b498cb1ea1ad69ddbbf631 4e8ec5bf2.jpg[/img]
cylinder 4 ohm reading

cylinder 3 ohm reading



these are some photo's currently @ 170,000 Miles, first time having the injector's out
and i am doing a OHM test to check each individual injector for function

(200+ is healthy) anything lower then that is signs of failure.

number 4 failed ohm test reading

oddly, the rear injector's have collected more carbon build up then the front, if anyone can chime in on how that developed i am curious.

cylinder 1

cylinder 4


















oil changes done every 6000 miles, full synthetic 0w20 Mann filter's
spark plug's every 25,000 miles

 

I love your post…
I have the same engine in my 2015 S550.
Thank you for sharing your experiences and maintenance schedule.
i look forward to more..
Be well
Chuck

 

Excellent post. Qs:
Why not install the pigtails? (depending upon when you learned they existed...)
I am having a hesitation when driving straightline, steady speed. Tires new, square setup. Transmission fluid last replaced 30k miles/ 5 years ago. it feels like either transmission has a momentary slip either due to tires perfect size (same size as before with no problem) or trans fluid. if you have run into this issue, suggestions appreciated. TY

 

Very informative post, thank you. Looking forward to your borescope photos. Just curious if you disabled the oil solenoid on yours. Also, what variety of Pennzoil are you running, and why 0w-20? Any used oil analyses on that regimen?

 

During 13yrs of ownership no check engine light (cel)