Steve Ekblad

Have a 2017 (purchased in 2016) GLC300 with 23K miles with a 4 year/50K warranty that expired ~6 months ago. Diagnosis is Cylinder 2 Piston Cracked. Received a quote from dealer $5300. Reading other posts, this may be a known issue with MB. Looking for feedback on other experiences. I have a case opened with MB corporate to cover the costs. Any input is appreciated.

chassis

Sorry to hear about the experience. This does indeed seem to be an evolving situation with the 2.0L turbo 4 cylinder M274 engine used on C300, E300 and GLC300 vehicles. Several model years seem affected across the several vehicle models.

Possibly it's a production run of defective quality pistons, or a marginal design by MB, or both.

Sugar_Mouth

Curious what octane fuel do you run regularly and have you deviated from that at any time?

Steve Ekblad

Premium unleaded, always. Never deviated.

Teckno

‘ This does indeed seem to be an evolving situation with the 2.0L turbo 4 cylinder M274 engine used on C300, E300 and GLC300 vehicles. Several model years seem affected across the several vehicle model “

Check the UK MB Forums for any issues, they have diesel and petrol models sold there and in high numbers.
Hopefully they can help with petrol examples and if MB UK provided extended goodwill warranty support.

Sugar_Mouth

I have noticed with mine even with 91 it knocks. The mid range they tuned into this thing is pretty aggressive, much more so than the newer model. I would think calming down the mid range boost pressure and or timing would help a bunch. I wonder if Mercedes has an update which helps with this.

DanD.

I don't want to get deep into gas quality, but I heard MB cant develop too many issues if runs on bad gas, not just low octane.
I personally use Chevron 99% of time, would use Shell if they build one close to me.
I do avoid Costco, Safeway or similar, even know there are so many discussions on this.

Sugar_Mouth

I think this varies quite a bit depending on location. I have logged knock retard with different fuel sources and found Costco to provide less knock retard than Shell or especially Chevron. I am in that tri state Cali, Nevada, AZ of junk fuel.

Srenaud

This is enough to make me want to sell mine. I've had a couple issues already. PCV Valve and Oil loom?pump? (they said it was 11 hour job i dont even want to know the price of that repair), luckly oil harness is covered by warranty but the PCV valve is not ($1700). I have the same model year but my power train warranty still has coverage. Shouldn't this be covered by that? My CPO warranty ran out last year but my powertrain will take me into next year.

Keep us updated on your case with MB corporate. It seems like these design flaws are popping up with alarming frequency with the 2016/2017 model years, wouldn't be bad if they weren't such incredibly expensive repairs. One step closer to getting rid of this car, its a shame because I love it.

NJCMB2018

I purchased a 2018 GLC300 with about 38k miles from MB Marin in NorCal and to date it has spent over 50 days in service, almost half the time of short ownership period. The first issue came up about 5/1/21 and was indicated by the check engine light. I brought it back to the dealer, disappointed and it was determined to be an air intake hose. It made me doubt the process of an apparently ' certified pre - owned ' vehicle. On 7/28/21, I had a major mechanical failure, the engine stalled and sputtered to a stop, the check engine light went on again and the vehicle was disabled. I had it towed back to the dealer service department and after a week of diagnostic work, it was discovered there was a cracked piston. They recommended a full engine replacement. Retail cost for a service of this type would have been in excess of $20K. But it once again, went under warranty.

I was blown away that the vehicle would need a service of this magnitude. It totally shattered my confidence in the reliability of the car - It seems a factory defect to me and the opinion of many trusted friends with whom I've discussed the issue with, including one who is a professional formula one driver. There is no margin for another mechanical failure here with legal / lemon law recourse, it seems to me.

I let MB Marin proceed with the service, I'm being patient with them for now but I am in discussion with MBUSA manufacturing to explore my options for buyback and replacement with the same make/model. At the very least, I will pursue an extended warranty at dealership cost as there is less than 18 months left on the existing. The dealership was just acquired by a large auto group and I'll make sure that the senior leadership of the organization knows about this failure. Very concerned. - Nicola

brumjeet

One month back my car slowed down and vibrated unusually. Diagnostic done- piston rim break. Trying to get a new engine from MB

chassis

Sorry to hear, please keep the thread updated. The M274 engine clearly has an issue with piston cracking. The M264 may also have the same problem because the engines are related, but too early to tell with the M264.

I would stay away from the M274.

Sugar_Mouth

Bought mine from the same dealer. Mine is knocking/detonating quite a bit even with 91 octane. This is exactly the type of behavior that will cause a piston to fail. I do not have faith in the long term reliability of this engine. I know this could be resolved through tuning. I think I'll ask my local dealer if there is an ECU update.

mikapen

I wonder if that's why M-B is so insistent on using 91 aki gasoline. But you'd think that the knock sensors would intervene and reduce power, timing advance and other things.
Lots of owners disregard that warning, and IMO are "Penny Wise and Pound Foolish."

trygve11

I operate a specialty shop in Kansas City (Royal Autowerks) and just bought a 2016 C300 with 68K on it from a client with the loss of compression on cylinder #1 and will perform the detailed teardown (and rebuild ultimately). My client has registered for this class action lawsuit. I recommend that anyone that has had the same concern, reach out to the CA law firm that is pursuing the class-action suit.

https://www.classaction.org/news/mer...ng-m274-engine

I am a former Ford engineer and MIT mechanical engineering graduate (Masters and Bachelors) and 39 years as a mechanic. I have engaged the law firm and will likely end up being the engineering and mechanical expert on this case.

I encourage you to get registered for the suit if you have suffered a loss. Do this before you dispose of the vehicle.

- Jason

karmikan

It seems highly likely that the problem is not specific to MB but is common to all small displacement, turbocharged, direct injection engines. The cause is probably not faulty pistons or manufacturing defects but Low Speed Pre-ignition (LSPI). This obviously does not abdicate MB from all responsibility as they should have used more stringent long-term testing procedures before releasing these engines on an unsuspecting public. The following videos explain the problem and suggest solutions much better than than I can. Hopefully they help.

karmikan

After a bit of additional research I've found some more info. Problem is that things seem a bit more tricky than I had hoped.

From the facts contained in the above videos, using API SP oil seems the way to go in order to minimize the damaging effects of LSPI. I searched for the oils recommended for a GLC300 on the Mobil1 and Castrol websites. Mobil1 recommends either 0W40 or 5W40 both of which are API SN which means that they don't address LSPI, in fact they have the highest concentration of Calcium (seemingly a major cause of LSPI). Castrol recommends 0W30 which is even worse with an API of SL.

The closest SAE grades with an API of SP to the ones recommended are 5W30 for both brands. Several web sites list 5W30 as an acceptable substitute to the recommended grades. I've been using Mobil1 0W40 (bad choice!) on my GLC since new but I'll be switching to M1 5W30 API SP as soon as possible and keeping my fingers crossed that I haven't incurred any appreciable engine damage.

tbirdvet

I believe Pennzoil Synthetic Euro 0W40 meets the new API SP specs. Good price at Walmart.

DanD.

MB recommends to use oil with Spec 229.5 for GLC 2018, I would not go by API SP specs.
I used all 5W40:
Liqui Moly 2332 Leichtlauf High Tech 5W-40
OEM Mercedes Benz Geo 229.5 5W40
Valvoline European Vehicle Full Synthetic SAE 5W-40

You can see oil analysis below, oil changes every 3K miles, but viscosity isn't perfect.

karmikan

The Pennzoil web site says that their 0W40 and 5W40 are both rated at API SN PLUS.

Looking at your PDFs, the Calcium content measures an average of 2700 which is huge. The magnesium content averages only 15. According to the info presented in the videos, Calcium is a major contributor to LSPI and magnesium is the substitute to combat this problem so your oil is the exact inverse of the API SP spec. Maybe ask yourself why API SP was developed (no doubt at great cost) just at the point when small-displacement, direct injection, turbocharged engines are out there in sufficient numbers and with sufficient mileages to encounter increasing instances of piston failure.

My guess is that MB will eventually come out with a new oil spec for their turbo, direct-injected 4 cyl engines when a 0W40 oil meeting API SP is developed. Until then they will continue to specify oils containing high levels of potentially engine-destroying calcium. Unless of course bad publicity and lawsuits force their hand. Pity.

tbirdvet

Their bottle of oil says it does meet SP spec. See this photo:

DanD.

And it has MB spec 229.5 just bought two cases ))
Thank you for the tip.

karmikan

You're right, thanks. Guess Pennzoil didn't update their web site. On my way to get some.

mikapen

It sounds like you are attributing flame front propagation to oil choices, and that calcium is a culprit.

I find that hard to believe, unless it's in the 2 liter 476 hp AMG version (recently announced). Which I'll bet has a combustion chamber designed for its high pressures and a progressive flame front.

I'd like to learn from your sources. Please share.

crconsulting

Couple that with carbon in the combustion chamber/piston top causing even a slight bump in compression of the M274 (10.3:1) makes this even more critical. I wouldn’t count out questionable “supreme” gas, out of spec, or contaminated either…..

Perhaps some enterprising tuner should start selling “De-Tunes” (for crappy gas spec). 🤨