m1l3n

Hello,
I tried searching this and the CLS forums for a thread which has all the M278 issues but i couldn't find one (or they were buried). I'm conducting research as I want to take on the monumental task of putting an M278 in my W204 4matic C300.
I've done a lot of digging and the thing that keeps coming up is the tensions on the earlier M278 models. I also came across another scary thread of an engine from GL which had to have its cylinders honed at 70k miles because of low compression due to what appears to be Silitec coating wear resulting in scratches. The engines I keep finding on the market are at the 60-70k mile range and as so i wanted as much input from people who have dealt with this engine as possible.

As a whole, what are your impressions of the M278?
How many miles do you have on yours and have you had any major issues?

Amr_c63

These engine are really reliable for what they are . Things you need to watch for are the chains were updated in the later models I think 13 or 14 and up had the updated ones . Also the coolant lines for the turbos tend to leak from time to time . And last but not least the camshaft sensor suffer from oil getting into the harness .

nota_amg

120k miles on car/engine. I've made 650hp, +750tq for the last 15k(550/650 for 10k before that) and I'm very close to the fuel system's limit, even using AMG in-tank pumps. been pretty reliable. I have a stock front driveshaft on the way now, but it's u-joint was damaged when I bought the car(put on aftermarket one last week and twisted it in half like it was a paper towel roll! smh).
I have a slight drip from front cam adjuster cover plates that I need to reseal and I'll be doing the turbo waterlines, replacing the I/C pump with a CWA100 and replacing the t-stat/housing soon, just for preventive measures. Keep up on the maintenance and it'll treat you right.

m1l3n

That's wonderful to hear. The thought of having something similar in a 4matic car that is a few hundred pounds lighter is just sooo tantalizing.
s the drip from the cam adjuster something common?

nota_amg

yeah, the o-rings on the adjusters are seeping as well as the plate that they are mounted to(it is sealed to the head with black sealant and uses one-time use screws that must be replaced as well).

I believe your C550 is going to run really well. I'll be following you to watch your progress on this. I'm running 11.3 @ 122 in the summer heat with high DA. With some stickier tires and cooler weather, looking to break into the 10's by EOY. Still on stock turbos

m1l3n

Looking at engines i also got an additional question. Besides an oil pan that accommodates for the front drift shaft to go through it, are RWD and AWD engines the same?
Where im going with this is, if i get a better deal on a RWD engine I'd rather do that and change the bottom part of it myself.

S. Madman

Yes they are. In fact all m278 are equal on the long block. The 2014 and up E's have additional cooling lines and reservoir. There have been revisions for sure. But it not like a BMW where they figure out the meaning of life to do a one letter revision.

MBNUT1

What about the valve seat issues? https://mbworld.org/forums/gl-class-...re-solved.html

chassis

My understanding of M278 issues are:

- valve seats as mentioned
- piston scuffing
- timing chain
- oil in harness from cam sensors

m1l3n

Is there a year/engine number from which point on these issues are resolved?

jonUF02

I just bought a CPO 2015 GL550 and starting trolling x166 threads, scary that one thread with the engine tear downs. I've been more than happy with my E550 for 5 years and no problems other than the AC compressor dying last week. I have 1 year CPO warranty on the GL, might extend it if anything seems funny in the next year. I don't see that scary stuff on the W212 side.

chassis

@m1l3n I haven't seen engine numbers or years mentioned on the site. Need to dig up all the relevant threads.

https://mbworld.org/forums/gl-class-...78-engine.html
https://mbworld.org/forums/gl-class-...rebuild-2.html

MBNUT1

This contains the TSB which identifies a starting date for the valve seat issue but I have asked in the thread if anybody knew the end date and haven't gotten a response.

https://mbworld.org/forums/gl-class-...re-solved.html

nota_amg

-Valve seats: I believe is an issue with all engines(M278/M157). The theory is, there was an issue with the way they were machined and/or installed and for some reason(physics...) the exhaust seat for Cyl 5 actually falls out of the head casting due to excess heat causing the head to expand too much relative to the seat's outer diameter.

-Piston scuffing: I'm not aware of personally and have not looked into.

-Timing chain: Here is a quote from another thread about effected engines-
"M278 engines affected as follows:
Engine 278:
1) Up to engine number 278 9xx 30 073273 install check valves and chain tensioners
2) From engine number 278 9xx 30 073274 up to engine number 278 9xx 30 103675 (February 2013) install check
valves only (optimized tensioners installed in this production range)"
Here is a link to a post with the bulletin info:
https://mbworld.org/forums/5738609-post153.html

-Oil in harness from cam sensors: this is a sensor issue. There a 4 cam sensors, just pull the connector and check it for oil. If there is oil, clean thoroughly with brake cleaner and allow to dry(use compressed air if possible). Then clean it again. Replace the cam sensors that are leaking oil and you should be good to go. I had oil in my harness and it actually wicked down to the driver's O2 sensor connector. I replaced all my sensors early on when I bought it last year. I had an engine light for Left Front(precat) O2 sensor and car started running like poo. Found oil in the connector when I replaced the sensor. Cleaned it very well, let it set disconnected overnight, recleaned it the next day and put everything back together. I pulled the exhaust back out for some other work 2 months later and checked the connector and it was still dry. Some people have had to pull motor and replace their harness, lucky mine was not that bad.

MBNUT1

I guess it's a good thing that EV's are coming because Mercedes seems to be losing the recipe for successful ICE design.