Floridah

Hey everybody! New member, but been lurking in the forum for a long time! So ran into an issue with my gl. Out of nowhere it started making a knocking noise which sounds pretty bad. Driver side more on front of the motor. No misfires, no loss of power, no check engine light. I took accessory belt off, noise did not go away. Knocking does follow RPM’s but gets much quieter almost goes away once motor reaches 2k, loudest at 1k rpms, if i rev it up to 4K sound kinda reappears but very quietly, and once rpms drop back to idle it loud again. Currently 86k miles, never had issues with it before. Obviously I’ve parked it and not driving it for now. Out of warranty and don’t really know to many mechanics locally, anyone has ran into this issue before? Or know what could it be? I’ve added couple links to two videos I’ve made and uploaded on youtube.

hambone1983

Not an expert but that sounds bad. Subscribing to see what others say. Good luck man. Hope this isn’t something major.

BlownV8

To me, it sounds like an exhaust leak.

Floridah

i wish that it would be the case, but sound is definitely coming from inside the motor, sound more like top of the motor

arsupisemnet

Buy yourself mechanics stethoscope for 5 dollars at Harbor Freight.
​​​​​​You will be able to isolate location of the sound. For me it sound like hydraulic lifter at one of the valves.
Or you can try to do engine oil flush before oil change and see if it goes away....

Floridah

sorry took such a long time to get an update! Indeed hydraulic lifter there bad, 6 to be exact. Noise didn’t go away, much quieter now but still sounds like a knock/slap that follows rpm range. You think my cam adjusters could of went bad?

arsupisemnet

How many miles do you have on your car?
I will have to disappoint you but usually camshafts in these engines didn't last long. There is an extensive wear on camshaft lobes, because of being not solid piece of metal part. As a result you will have a groove (as i had in mine ended up replacing some of camshafts), where knocking noise is just a tapper roller going in or out of groove. I would not worry much, unless it is annoying you.

geniushanbiao

It might be a little dumb to ask but what oil are you using in the engine and how often do you change it? Do you check oil level in between changes and how often?

Floridah

so finally had time to pull valve cover off, camshafts seem to have no scratches, or grooves. I’ve noticed if I press on timing chain, intake camshaft moves close to quarter inch, pretty much as much as chain allows under tension. Seems it’s not locking as it should.

Floridah

every 3-4K miles. Don’t drop more then quart of oil ever. 5w-40 Mercedes oil

Kaimir

Hi, bought my 2014 GL 500 in March 2020 at 75000 Km. I know this sounds low, but I` had it checked at the dealers and they advised me that they had seen the car in January 2020 with 73500Km on the clock. Anyhow, sometime around June of 2020, my car started to develop a similar knocking noise to that described here. My Service Centre guy told me that 7 of every 10 GL 500's have the same problem and it would eventually need an engine rebuild; estimated cost USD 8K. So if anyone can shed further light on the subject I would be happy.

p.s. I have new Aux belts and pulleys installed along with new chain tensioners.

Floridah

sounds about right, once I had my valve covers pulled of, we had tensioners replaced and upper chains, rocker arms and valve lifter on left side, had pretty bad premature wear, so whole side of new rocker arms and valve lifters got done as well, and noise didn’t go away, but got worse within a months. Oil started to change colour due to combustion gasses getting by piston rings, end of story it needed new engine. Due to weird COVID times, I had my friend run it through red auction with red light and all necessary announcements and ended up getting what I paid for it after driving it for a year.

mcoady1

Did yours do this on cold start and when warmed up? My 450 is a quieter version of your second video, but its completely gone when warmed up.

Thinking just a cold start piston slap that can be ignored, would be more concerned if mine was MY 2014 as it seems more prevalent than MY 2013. Also already at 125k.

ironhorse300e

I just went through the same thing. I ended up replacing the engine. Might need to put a boroscope in it and check cylinders

mcoady1

Here’s mine, first is cold(ish) start after sitting for about 4 hrs. Second is 10 minutes later, slap completely gone. Likely some scoring going on but want to be adequately prepared if a ticking time bomb.

OnlyGerman

OP: what was your mileage?

mcoady1

125k

Ricardoa1

70% failure rate?

mcoady1

I went ahead and did an oil analysis on my engine to see if the cold piston slap was a sign of impending engine failure (see previous videos in this string to hear). If these engines weren't susceptible of piston wear and cylinder scoring I would likely ignore, but here we are.

Fortunately the report came back positive and the abnormal molybdenum and boron relate to Ceratec. I appreciate the personalized comments from Blackstone as well. I was mainly looking for fuel in oil (as arsupisemnet noted prior to his failure) but the report indicates trace amounts were found. The interval for this oil sample was 9300 miles. Let me know if anyone interprets the report differently.

mcoady1

So today I noticed something interesting with my piston slap, which is usually present for +/- 1 minute upon starting the car after its been sitting for over an hour. The car was parked on a slope with the front facing downwards, and the piston slap was gone when I started it. I'll try tomorrow with the front facing upwards and see what it does.

If it were piston slap, I wouldn't think slope would affect it tolerance-wise?e

olesouthernboy

The M278 engine is not aging well at all. Just dumped my wife's 2014 GL450 96K miles. This car was extremely well maintained since new. Dealer serviced until we got it at 54K miles. We did the little crappy PLASTIC turbo water lines, chain tensioners, two trans services, two differential services, 5K oil changes with mobil European car 0w-40 and a few other things that I can't recall at the moment. Developed a slightly rhythmic roughness at idle but ran fine off idle. Pulled #5 plug plug and took a look and here is what found. We are now proud owners of a steel cylinder lined TOYOTA LS460. I am done with anything newer than a pre-Chrysler MB.

tadiguy

@mcoady1 Did you ever figure out what was the problem? I have the exact same noise that is present all the time except at >2500 RPM. I see most with similar noise just ended up replacing the engine (at any sign of cylinder scoring) without finding the actual root cause. My noise frequency is at exactly 1/2 the RPM so it points to something on the upper end. Rockers, lifters already checked and replaced with no difference in noise.

mcoady1

@tadiguy I have not and am just living with it. It always goes away after the car has been run for +/- 2min. I assume its piston slap but haven't ruled out it being something else. My oil analysis didn't show gasoline in the oil and I just add Ceratec at oil changes.

I saw on the CLS forum another user had a ticking noise from a faulty spark plug that I guess was slamming around internally. I haven't replaced the spark plug yet to rule that out but a possibility (albeit unlikely). Since mine doesn't do it when front of car is sloped downwards, I wonder if its a matter of something not oiling up properly when starting.

tadiguy

Thanks. I saw the CLS posting regarding spark plug defect earlier. I inspected mine and replaced them with no difference. I think I've also ruled out the fuel injectors as a potential cause.
Both of your noise and especially @Floridah OP description is ditto with how mine behaves so I'm convinced it a common cause. I even did some spectral analysis on your audio clips and it's low RPM suggesting something driven by the cam. If it were piston slap for instance, I'd expect it to slap every time it comes to TDC on both compression and exhaust strokes (or going to BDC for both intake and power strokes) and so would correlate with crank RPM instead of cam revolutions. I also observed that the upper tensioner piston pulsates a bit and is in sync with the noise rhythm (not sure if the pulsation is normal), but I couldn't determine conclusively if it's coming from the tensioner. I've swapped the tensioner with a known good used one I had laying around with no difference.

I've attached some scope analysis of the noise (blue spikes) correlated with cylinder #1 ignition event (red spikes). From the M278 firing order my noise coincides with cylinder #2 firing event. Also notice the 300 RPM of the noise (engine idling at 600 RPM). Someone on the CLS forum ruled out rod bearing and hence rod knock. It really must be something in the head. Very perplexing noise indeed. I'm ready to button it up and do some road test to see if I can characterize this further (I bought it in this state as a project car so I haven't really had the opportunity to road test due to concern about potential catastrophic failure.

mcoady1

Interesting!

Thanks for the feedback. So possibly the chain tensioner could be causing the knock in my case? I always assumed it'd be a rattle with tensioners but maybe its temporary noise from the cam shaft until oil has built up. Maybe valve lash / unseated valve knocking?

Odd that mine only does after sitting and yours at all times. Must be something with a tight clearance affected by oil pressure/presence.