shafowz911

Hello All,
I recently bought a 2013 GLK350 4Matic. The car has good service history.

The car starts right away with no noise at all during both cold and hot startup. However, if I drive the car and let it sit for half an hour or an hour, then the startup will have loud knocking/rattling. The noise only happens with a warm engine and doesn't happen every time (sometimes war startups are smooth). I was suspecting the chain tensioners but not having any noise during cold startup made me want second opinion. Specially that many people reported having noisy startup even after replacing tensioners.

Thanks!

andreigbs

Top end knock or bottom end knock? Some of the earlier M276 had slightly off size main bearings that allowed for some knocking until oil pressure was stabilized upon starting. If it's just a second or two and then it goes quiet, I wouldn't worry about it too much.

We will assume it has had proper spec oil (MB 229.5) and quality filters all its life, changed at the appropriate intervals; if not, start with that.

Mmr1

Did you change the oil and filter , if not do it and use a quality German filter.

shafowz911

I didn't really try to identify whether it's a top or bottom knocking but I will do this today unless it needs a stethoscope.
Interestingly, the startup noise became more pronounced after I changed the oil and filter. I currently have M1 0W40 with a Hengst filter. I was thinking about trying a Mann filter with Motul 5w40 on the weekend.

andreigbs

I believe M1 Euro 0W40 is approved for MB 229.5 spec, even if a bit on the thinner side (the 0W-xx) so it should be fine. From my experience, Hengst makes good filters, I've use them and Mann/Mahle regularly with no issues.

If you've got the proper amount of oil in there, it's likely not from the oil/filter. Locating the knocking would be helpful; have someone start the engine while you listen outside with the hood open. You also didn't clarify whether the knock goes away after a second or two, or continues until it's shut down again. If the former, and the knock seems to come from the bottom, it's probably the bearings issue that's well-known. If it's from the top of the engine, it might be something to do with the valvetrain.

I assume you're using premium fuel and are not experiencing that kind of knock or pinging, as it's often called.

calder-cay

FWIW, 5-40 Mobile 1 (South Central Texas, so winter about 1-2 months), Mann filter always. So far, no issues.

shafowz911

I always used premium fuel. Here is a video of a warm engine start:
it seems like the noise is coming from the top

Bill F

Sounds like a leaking lifter as the noise goes away so fast. I would use a slightly heavier oil 5 - 40 may help. I used Motul oil in my last car and several shops near me use it for high end cars. More expensive.


How many remember the old days when a can of STP fixed everything. Not good for fuel economy LOL but who cared.

If nobody remembers the old STP I have to be the oldest person here.

Mmr1

It sounds bad, timing chain tensioners?

andreigbs

Call me crazy, but it almost sounds like it might be the starter. When you first crank it up and the engine catches, you can hear what I think is the starter going into over spin mode, then as it retracts back from the flywheel it might be touching flywheel teeth before fully retracting.

Lifter(s) without oil or oil pressure might also be it, hard to tell without being there, but you changing the oil recently kind of rules that out for me. Another option might be one of the rollers being a bit loose and making noise until getting spun up to the right spinning speed at idle, but that seems less likely.

I don't think it's the timing chain tensioners, they sound pretty quiet after the initial 1-2 seconds of noise, but I couldn't rule it out either. It also doesn't sound like the bottom end main bearings issue I had mentioned; I had a C300 with the early engine and can recognize that noise anywhere.

I would be curious if you could crawl underneath, and without the bellypan on, if you could see the starter in operation when cranking it up. I wonder if there's a visual line of sight on the starter and flywheel, honestly, don't remember from my gasser days.

Mmr1

Even if you don’t have a stethoscope a broom handle will work , yes you need to locate it.

John CC

I still use STP mixed 50/50 with SAE 50 engine oil as assembly lube.

C300fan2

Timing chain tensioner possibly. Here is a youtube video about common issues with the engine that goes into detail regarding what you might be hearing.

shafowz911

It seems like opinions are more toward lifters or chain tensioners. What is surprising is that it doesn't happen with cold and hot start. Only warm engine starts. I will probably start with an oil change to 5w40 and Mann filter.

andreigbs

This is a diesel in your video; the OP has the gasser M276.

C300fan2

oops I assumed diesel sorry

Odd Piggy

Trying 5W-40 sounds like a good choice. I had a BMW 335i that rattled on Mobil 1 0W-40 that I stocked in bulk. Pulled it back in and switched to Castro Edge 5W-40 A3/B4 and rattle went away. I think viscosity is more important than brand.

FYI - I have used Mann filters for years, but what’s in the MB box is either a Mahle OX814D or a Purflux L394. I used the L394 in my ‘15 GLK350. Both have a bit more surface area than the Mann in this application and maybe a lower pressure drop.

shafowz911

The 0w40 worked pretty well for my M272 but it seems to be pretty thin for the M27 for some reason.
thanks for letting me know about the filter, I will try to find one of these filters with the larger surface area.
Thanks!

Odd Piggy

FCP Euro has the Purflux L394.

Mmr1

Diagnose its location with a stethoscope or broom stick , that sounds serious , if it’s a lifter try an oil flush cleaner. But it sounds like the timing chain and that could be catastrophic. I’d figure out what it is first.

juanmor40

Sound serious. Please either get the stethoscope, the broom stick or a hose and pinpoint the area of the engine that noise is coming from.

How many miles on the engine? 2013 M276 engines can be within the TSB range for chain tensioners and timing oil check valve service. If the engine was not TSB serviced and ran with the rattle for long, two common issues are: damaged locking pin within the VVT (noisy), and spun reluctor wheel behind the VVT (quietly moving the timing until a code, or no-start condition)

If the noise is behind the timing cover --> my guess in on the VVT locking pin

DATA.. more DATA please.

Mmr1

Different oil won’t fix that crazy noise

GLKwanter

I can't believe the all over the map advise you've been given here on this incredibly common problem. It can lead you astray worry you needlessly and waste your time and money.

100% that is the dreaded "startup rattle". There's a TSB for it. And as would be expected a lot of misinformation.

Specifically what you're hearing, and why you're hearing it at warm startups, is the timing chain slapping, due to the upper timing chain tensioners not getting their oil quick enough. The chain is not stretched it will last the life of the engine.
Some, including Mercedes to cover their a$$, will say it's the upper timing chain tensioners losing their oil when the engines off, and that putting a check valve behind the upper timing chain tensioners will solve the problem, but that was never the problem off the showroom floor, and the check valves often hasn't solved the rattle for many.

The startup rattle arose for everyone who has it 60k or later. And the one thing they all have in common is not changing the oil every 4,000 to 7,000 miles.

The startup rattle is an oil starvation issue. Not a didn't hold on to oil problem, but a didn't get oil as quick as it did when it was new problem, due to build up in what is a very tightly designed m276 engine. Albeit incredibly reliable and worth fixing.

Eventually you will get an intermittent check engine light for cam position sensor. The slapping eventually rounds over a pin in the vvts, the first one of which is bank 1 intake, causing a labored idol at startup. You probably already need to replace Bank One intake VVT as well as upper timing chain tensioners. If you keep going without addressing the problem you will spin the the plates behind the vvts on the camshafts and then the price goes way up.

I had this exact issue when I bought my GLK350 at 134,000 mi. The dealer hid it from me by having it prestarted and I had no clue of any of this. At 135k I changed vvt's and upper timing chain tensioners and the rattle didn't go away, although labored idol at startup did go away. After 2,000 miles of running Motul 5w40 one day I said to my wife, "have you heard the rattle recently?" It was gone and it hasn't been back for 8,000 miles. The parts need to be replaced, but that's not the problem, the gunk is. I have heard of people replacing one quart of motor oil with 1 quart of ATF for 500 miles before oil change because it's full of detergents. Could help speed up the process of cleaning. It's the diet the m276 needs when it gets higher mileage on it. That Eco crap is too thin. It was used to squeeze mileage out of the engine at the expense of longevity.