Just completed my 120k mile service over the weekend...a few observations.
 

After 6.5 years of ownership and 120k miles later, I have now replaced the spark plugs TWICE in my 2012 M276-C350...and from my observations of the plugs both times (did both myself), I can confidently say that Mercedes is definitely on the conservative side by stating that it should be replaced every 60k miles. FWIW, the ORIGINAL plugs that came with the car were German Bosch ZR6SII3320. I purchased my 1st set of replacement plugs from Amazon (also German Bosch ZR6SII3320) however I switched vendors to FCP Euro on the second set once I found out that Amazon started selling Chinese (possibly fake) Bosch ZR6SII3320. I can confirm that the Bosch plugs I ordered from FCP Euro were in fact made from Germany in case this matters to some.

Apologies for no pictures (you'll just have to trust me on this one), but the reason why I believe the change interval is conservative is when comparing the old plugs to the new, the condition of the tip and the gap between both plugs is near identical with the exception of discoloration. There were also no signs of carbon build up, although I do use Redline SI-1 religiously every oil change. I'm going to continue to service this car by the book, but knowing what I know now, and if I can rewind time, I would probably do 80k mile cycles instead.

Some other observations/surprises:
You have to remove BOTH the engine air filter box AND the ECU when changing the plugs.
1 - I was surprised at the amount of dirt that was collected INSIDE the airbox. Thankfully none made it to the other side of the filter, but since you are going to move the airbox out of the way anyways, you might as well take this time to clean/inspect it. I also noticed that because I've removed/reinstalled the accordion hose (that connects the box to the air funnel) so many times in the span of ownership, that air gaps started to form in the clips section so not all the air is coming in from the front...but this was easily fixed with gaffers tape.
2 - This one shocked me...but when I unplugged the ECU unit, I noticed roughly a table-spoon of oil that was pooled INSIDE the socket that you lift the main cable up from. There was obviously no damage (I can only assume the oil was non conductive), and the unit was sealed pretty good for the oil to have pooled there instead of leaking down into the circuits, but the concept of HOW the oil got there in the first place still boggles my mind. After draining/cleaning it, I inspected the electrical wires to see if there was oil running down them and nada. I'm thinking the oil must of been sitting there for at least 60k miles?! This is unlike me to not have noticed, but it's my only explanation.

Other than the above 2, everything still runs great. MPG is still good and just the other week, I was able to hit a 29 MPG tank average for 430 miles.

Gracias, amigo.......

C250 here - with the 1.8 cylinder turbo four. Would your rewinding of time hold true were you to have (no offense meant) the C250 4 turbo?

I'm at 36,000 - but I am worry prone. I keep tabs of the MPG - this has provided good feedback over time.

Thanks,



ez

I honestly don't know. Different engine, and it's a turbo so I'm assuming different operating temps. I'm simply reporting back the pattern on what I've seen on my car for those with the exact same setup. I also haven't seen how/where to change it on the 250, so if it's easy enough, it might not be a bad idea to just stick to the manual.

I recently replaced the spark plugs in my 2013 C250 at 107K miles. I purchased the vehicle three years ago at 39K miles and the plugs had never been changed to my knowledge. The reason I did not change earlier is that there were no drivability issues and the gas mileage was consistently between 30 and 32 mpg. I do change oil and filter every 5K miles (old habits die hard) and the air and cabin filters every 20K miles. As edgalang reported I saw no problems with the old plugs. The only major difference was that the spark gap was larger on the old plugs.

Changing the plugs was very simple. Remove the plastic cover, unscrew and remove the coil on top of each plug, then replace the spark plug. Smear a little anti-seize on the threads of the new plug before torquing to spec. No other components had to be removed or disconnected. Total time start to finish was around thirty minutes.

Alex

Many thanks Señor Lynch,

My C250 coupe will be under 50k about 15 months from now..........

Thank you for the feedback. The little (CPO) coupe has been flawless since purchase at 23k. I sorta wish I could get another extended warranty.

(It's a beautiful little car - my better half test drove a 2019 C300 coupe. She told the surprised sales guy "I prefer my C250"...............

It's all good.

best,


ez

It is called oil migration by some people.


https://static.nhtsa.gov/odi/tsbs/20...83664-6903.pdf


https://forum.e46fanatics.com/showthread.php?t=1236408


Clean oil is insulating I guess, but not used oil with already contamination in it and may able to carry some electric signal.
Electric Transformer uses oil for cooling. Special Insulating Oil.
My dive computer is oiled filled (special oil ) and its circuit board and battery in indeed immersed in oil.

My plugs after 4 years and 11,000 KM. I replaced them anyway.
https://cimg2.ibsrv.net/gimg/www.mbw...dd447b882c.jpg

https://cimg7.ibsrv.net/gimg/www.mbw...9394710b6b.jpg

Since I bought the car used at 4 years old and 10,000 KM, I kinda "RESET" the maintenance and wanted to start fresh .
I bet the previous owner who goes to MB authorized workshop simply follow MB by the book and 10,000KM even at 4 years , I bet MB NEVER replaced the plug.
I don't know what exactly are the brown oil like film on the plugs thread, but I don't like it because it may offer electrical resistance.
I bought MB original plug, I know its a Bosch but I want the convenience and not to worry of fakes too.
.

Airbox C350:
C350, after my guarantee expired, I also discovered the airbox filthy, dealership never cleaned it, just replaced the filters. My airbox has two holes to let air or water through not sure about the water if flooded, but they were both completely blocked, not sure what the purpose of these two holes are, probably airflow in and out engine sucks air as required. Maybe with these holes blocked it can cause a problem at high speeds as air is compressed inside tubes from the front.

Plugs:
I am not sure if plugs are in too long period you may have a problem with threads getting them out-?

edgalang, thanks this is great information. With the M276 in the C-Class, did you need to remove the intake manifold or engine bay bulkhead? I understand that both of those added steps are needed for M276 spark plug change in a W166 GLE. How are the engine peripherals holding up: water pump, a/c compressor, radiator hoses, etc.

Airbox and ECU only per my initial post. At first I was annoyed that I had to remove anything to access the plugs, but I guess this isn't so bad since this would be the prime time to check on the condition of both items to clean them. As far as everything else, everything checks out, however do take in consideration that I live in California, where the car rarely (or have ever) experienced freezing or desert like temperatures and the car is garaged daily.

My 2012 C250 sport is around 117k miles. Some worthy things to note done to car since then: replaced spark plugs, engine coolant tank leaked ($600 fix), had misfiring in one of the cylinders which caused car to go into limp mode (ouch). But I still daily and love the hell out of this car but this year I may switch vehicle as I will graduate from college. Currently looking into 2017+ C63S and F80 M3. There is a local 2013 C63 with red brake caliper package but gas prices in my city is around $4.39 right now LOL.