[carguy]

I'm curious if anyone has experienced the following problem. I have an '08 E350 with 53k miles. Since about 30k miles, I've noticed a very heavy engine knock for 1-5 seconds immediately after startup. It sounds like bump, bump, bump, bump, etc. It happens only very occasionally, on a fully warmed engine that has been left to sit for 1-3 hours. It hasn't gotten any worse over the past 20k miles.

I've done a lot of research on the subject. It's definitely not a light tick or tap coming from the valve train or even a piston. It's not coming from the front of engine around any accessory belt parts (alternator, power steering pump, etc.). It is a very heavy sound, as if you lifted the corner of a piano a quarter-inch off a wooden floor and dropped it over and over. I suspect it's a main crankshaft bearing wobbling inside the block, just as oil pressure is building. I replaced the accessory belt, tensioner, and idler pulley, but it didn't help.

Is there any remedy? Can it just be ignored? I use Mobil 1 0w-40, and some people have cured startup noises with Shell Helix motor oil 5w-40. I used Marvel Mystery Oil in the crankcase for 3k miles, and it reduced the noise a bit. I'm considering Lucas additive.

 

[chevota]

That's pretty weird and I can't imagine what it is. I'd put some Lucas in it and see how it reacts. I'd use the whole 32oz bottle which may put your oil level a bit high so you may consider draining that much out first. If you don't live where it's well below freezing I'd lose the 0W too. Even when I lived where it dropped well below freezing I used 10W at min. I did buy some 10-30 last time but I also add Lucas, 60wt and misc other crap in there to thicken it up.
Some may chime in about how the oil companies and car mfg know what's best, and they do but their hands are tied by the government. Picture the president giving a speech while the real powers that be hold a gun to his ribs with one hand and a script for him to read in the other. That's how I picture it when a car mfg says to use light oil.
Add it while the eng is running, or at least hot because you don't want to do a cold start while it's trying to suck a slug of that stuff up in pure form while cold.
I would buy the original Lucas because it's much thicker than the synthetic. Considering the point is to see if thicker oil will dampen the noise and you have water in there now you need as thick as you can get.

The only time I hear an eng making that sound is when a rod bearing is shot, but they get worse fast and the rod or eng will fail shortly after. Unless maybe you drive like Ma Kettle I suppose it may last a while but with that thin oil I don't think it would last a few miles. Plus the sound doesn't go away much after the 5sec you mentioned, it just gets dampened a bit. So I'd say with 99.99% certainty it's not a rod bearing. Mains rarely have issues and they won't make noise like that either, probably won't make any noise at all but they will cause the rod bearings to fail so it's not a main.
I take it back, I have heard similar with a bent rod hitting the block but it also continues to make the sound all the time.
High pressure direct port fuel inj it is capable of making a lot of noise if something goes wrong, but I forget if your year has it.
For troubleshooting you could turn the crank by hand, with a ratchet wrench, while cold to see if you feel it binding up during rotation. Remember it takes two crank turns to get the cams to turn once which helps you pinpoint which of the two does whatever odd thing you may find it doing.

 

[carguy]

That's pretty weird and I can't imagine what it is. I'd put some Lucas in it and see how it reacts. I'd use the whole 32oz bottle which may put your oil level a bit high so you may consider draining that much out first. If you don't live where it's well below freezing I'd lose the 0W too. Even when I lived where it dropped well below freezing I used 10W at min. I did buy some 10-30 last time but I also add Lucas, 60wt and misc other crap in there to thicken it up.
Some may chime in about how the oil companies and car mfg know what's best, and they do but their hands are tied by the government. Picture the president giving a speech while the real powers that be hold a gun to his ribs with one hand and a script for him to read in the other. That's how I picture it when a car mfg says to use light oil.
Add it while the eng is running, or at least hot because you don't want to do a cold start while it's trying to suck a slug of that stuff up in pure form while cold.
I would buy the original Lucas because it's much thicker than the synthetic. Considering the point is to see if thicker oil will dampen the noise and you have water in there now you need as thick as you can get.

The only time I hear an eng making that sound is when a rod bearing is shot, but they get worse fast and the rod or eng will fail shortly after. Unless maybe you drive like Ma Kettle I suppose it may last a while but with that thin oil I don't think it would last a few miles. Plus the sound doesn't go away much after the 5sec you mentioned, it just gets dampened a bit. So I'd say with 99.99% certainty it's not a rod bearing. Mains rarely have issues and they won't make noise like that either, probably won't make any noise at all but they will cause the rod bearings to fail so it's not a main.
I take it back, I have heard similar with a bent rod hitting the block but it also continues to make the sound all the time.
High pressure direct port fuel inj it is capable of making a lot of noise if something goes wrong, but I forget if your year has it.
For troubleshooting you could turn the crank by hand, with a ratchet wrench, while cold to see if you feel it binding up during rotation. Remember it takes two crank turns to get the cams to turn once which helps you pinpoint which of the two does whatever odd thing you may find it doing.

Thank your so much for all the good info. This noise has been driving me crazy for several years now, given that it is such an expensive car.

I agree with your first two paragraphs entirely. I'm glad to hear you've used Lucas with good results. On which engines have you tried it? I was going to opt for the Low Viscosity version because my engine has variable valve timing, which I've read is sensitive to thicker viscosity oil. I don't live in a cold climate, and the car is parked in a heated garage in the winter months. I agree that Lucas and MMO additives are not nearly as dangerous (or ineffective) as people think. What's more, the oil companies that make the "approved" MB 229.5 vary the oil quite a bit, so adding your own additive to quiet a noise is not a terribly idea.

As for the rest of your answer (about rod bearing and not crankshaft bearing), I think I have to clarify my problem a bit more. It happens only very occasionally, when the engine has cooled for some time. I only hear it a couple of times each year, usually in the summer. The noise disappears entirely after a couple revolutions of the engine, so obviously oil pressure is at play. I think it is a matter of some engine components cooling at different rates than others, creating micro gaps that are outside tolerances, but only at very specific temperature differentials throughout the engine. So, for that reason, tearing into the engine and checking tolerances with a micrometer would likely not give accurate readings. If it really is a main bearing(s), it's this infrequency that explains why they have not failed by now. The tolerances on the mains are extremely tight compared to engines 50 years ago, allowing only .001" of an inch variance (not the old, .003" rule of thumb). Lastly, I do not have direct fuel injection, only port injection.

I have found many complaints on the Internet about late-model MB engines making noises briefly at startup, even with as little as 8k, so I think I'm in good company. I have also read in one repair manual that quick startup noises -- valve train and rod & main crankshaft bearings -- are not catastrophic, continuing for tens of thousands of miles without damaging the engine. Many people report that most dealerships usually dismiss these problems as "normal." I read about main bearing failures in the pre-2008 M272 engine, due perhaps to manufacturing defects, but it's not clear if those problems pertain to my 2008.

 

[chevota]

I rec'd an email you replied but it's not here, and the email didn't include your entire reply, the last words were "I was". To answer what I did see; I do that on all my cars, which is currently a '16 E550. I had a '13 E350 too which got the same treatment. A CLK320, 190E, ML320, ML55 plus whatever misc other vehicles and stuff like generators. I've done this since my first car at 16 because thicker oil simply protects better period. If it says 10W30 it's just 10wt with thickeners, not 30wt. If I lived where it was so cold that thicker oil was an issue I'd buy a block heater or pre-oiler instead (I want a pre-oiler anyway btw). Plus Lucas sticks to parts better so cold starts are less an issue. How much it helps I can't say, but it does help. If your eng is freezing cold then probably not such a good idea but not a concern for me.
I can't say how well my thicker mix-o-stuff works but I firmly believe it works much better than what virtually everyone else has in their cars. I'm also much harder on engines than most so I especially feel the need for it. At some point oil could be too thick but I don't believe I'm anywhere near that point. It may drop into the low 30's at night in the worst part of winter but the eng doesn't. Last time I bothered to look at the eng temp on a cold ass morning it was >60 at 5am. I forget exactly but the point is it holds heat for a long time so when I see oil temp charts I'm feel I'm more than fine. So you just have to decide for yourself what your needs are, and if you want to add stuff like Zinc, Phosphorus, Moly, Boron, Tungsten or whatever bends your barb. I actually have all of them except Moly in mine. Why? Because I can
You might also consider Amsoil. It's better stuff and arguably the best oil period. I buy direct which requires an account that's like $10 for 6 months. That nets a good discount (25%?) + free shipping. I buy plenty of oil before that time runs out and it'll last me several years. They have all kinds of other cool stuff too. The Signature Series Amsoil is more expensive than the typical oil they sell so you can save a couple bucks a qt getting the regular stuff. Not sure what the difference is but the claimed miles per change is like 25k for the Signature. Not that I'd do that but I feel at 10-12k I'm in better shape than if I had the regular 12k oil. I think I read the difference was additives to resist acidity? Or that plus other stuff? I dunno but it makes me feel better using it.
So this last time I bought Signature Series 10W-30 and Dominator SAE 60. Then some syn Lucas from Walmart. I used 1qt of Lucas but I don't really know what the best % mix is for my eng and one seemed reasonable. If I used two then I'd feel like I should subtract one 60wt, but who knows. So again more of a warm fuzzy thing but it would be interesting to see data on different ratios of Lucas to make a better decision.
My RV generator I just filled got the same mix of oils but no additives (yet). My friend used cheapo dino oil in his gen and it seized. It had some good hours on it but I feel it would still be running if it had my mix. I also use a magnet to catch iron the filter misses, or in the gens case it has no filter so even more important. Just stick the biggest and most powerful neodymium mag that fits on the end of the drain plug. If you don't have an alum pan then the magnet may decide to stick to that and you have problem, so in those cases I use JB Weld. On my truck I actually installed a huge drain plug (1" NPT) which of course I had to put a huge magnet on It catches a lot of metal which is so fine you can't feel it so mixed with the oil it's basically thick ferro fluid in a big black spiky ball on the magnet. People assume filters catch everything but they're mistaken. In fact, all the engines I've worked on have a filter bypass so much, possibly most, of the oil is not filtered at all! I plugged the bypass in my truck because I just can't imagine not. I assume these cars have them too but I'm not taking it apart for that. If it wasn't for the magnet I'd likely devise a super filter to manually clean the oil now and then. I hear some people do that via an auxiliary filter using a small line that taps off the oil galley and dumps back to the eng somewhere so it's slowly working all the time. One guy told me he did that using a roll of toilet paper as a filter element, which he did decades ago in his offroad racing days. Seems like the fibers would start clogging the main filter but maybe they don't shed in oil. He probably used Scott brand which if you've had it you know what I mean. Meanwhile I've been eyeballing the 1 micron filters I use in my RO water filter setup. I have all the other parts including a powerful little elect pump. Now for the next few few days part of my brain will be trying to talk the rest of it into making said setup. It's also telling me to find some kind of filter material to put around my MB filter. Not the whole thing obviously, but like a 1" ring around it or maybe just a square patch. So >99% of the oil would take the easier path via the main filter but it would slowly catch stuff...
As you can see I spend way too much time thinking about stuff that very few others care about...

 

[carguy]

I rec'd an email you replied but it's not here, and the email didn't include your entire reply, the last words were "I was". To answer what I did see; I do that on all my cars, which is currently a '16 E550. I had a '13 E350 too which got the same treatment. A CLK320, 190E, ML320, ML55 plus whatever misc other vehicles and stuff like generators. I've done this since my first car at 16 because thicker oil simply protects better period. If it says 10W30 it's just 10wt with thickeners, not 30wt. If I lived where it was so cold that thicker oil was an issue I'd buy a block heater or pre-oiler instead (I want a pre-oiler anyway btw). Plus Lucas sticks to parts better so cold starts are less an issue. How much it helps I can't say, but it does help. If your eng is freezing cold then probably not such a good idea but not a concern for me.
I can't say how well my thicker mix-o-stuff works but I firmly believe it works much better than what virtually everyone else has in their cars. I'm also much harder on engines than most so I especially feel the need for it. At some point oil could be too thick but I don't believe I'm anywhere near that point. It may drop into the low 30's at night in the worst part of winter but the eng doesn't. Last time I bothered to look at the eng temp on a cold ass morning it was >60 at 5am. I forget exactly but the point is it holds heat for a long time so when I see oil temp charts I'm feel I'm more than fine. So you just have to decide for yourself what your needs are, and if you want to add stuff like Zinc, Phosphorus, Moly, Boron, Tungsten or whatever bends your barb. I actually have all of them except Moly in mine. Why? Because I can
You might also consider Amsoil. It's better stuff and arguably the best oil period. I buy direct which requires an account that's like $10 for 6 months. That nets a good discount (25%?) + free shipping. I buy plenty of oil before that time runs out and it'll last me several years. They have all kinds of other cool stuff too. The Signature Series Amsoil is more expensive than the typical oil they sell so you can save a couple bucks a qt getting the regular stuff. Not sure what the difference is but the claimed miles per change is like 25k for the Signature. Not that I'd do that but I feel at 10-12k I'm in better shape than if I had the regular 12k oil. I think I read the difference was additives to resist acidity? Or that plus other stuff? I dunno but it makes me feel better using it.
So this last time I bought Signature Series 10W-30 and Dominator SAE 60. Then some syn Lucas from Walmart. I used 1qt of Lucas but I don't really know what the best % mix is for my eng and one seemed reasonable. If I used two then I'd feel like I should subtract one 60wt, but who knows. So again more of a warm fuzzy thing but it would be interesting to see data on different ratios of Lucas to make a better decision.
My RV generator I just filled got the same mix of oils but no additives (yet). My friend used cheapo dino oil in his gen and it seized. It had some good hours on it but I feel it would still be running if it had my mix. I also use a magnet to catch iron the filter misses, or in the gens case it has no filter so even more important. Just stick the biggest and most powerful neodymium mag that fits on the end of the drain plug. If you don't have an alum pan then the magnet may decide to stick to that and you have problem, so in those cases I use JB Weld. On my truck I actually installed a huge drain plug (1" NPT) which of course I had to put a huge magnet on It catches a lot of metal which is so fine you can't feel it so mixed with the oil it's basically thick ferro fluid in a big black spiky ball on the magnet. People assume filters catch everything but they're mistaken. In fact, all the engines I've worked on have a filter bypass so much, possibly most, of the oil is not filtered at all! I plugged the bypass in my truck because I just can't imagine not. I assume these cars have them too but I'm not taking it apart for that. If it wasn't for the magnet I'd likely devise a super filter to manually clean the oil now and then. I hear some people do that via an auxiliary filter using a small line that taps off the oil galley and dumps back to the eng somewhere so it's slowly working all the time. One guy told me he did that using a roll of toilet paper as a filter element, which he did decades ago in his offroad racing days. Seems like the fibers would start clogging the main filter but maybe they don't shed in oil. He probably used Scott brand which if you've had it you know what I mean. Meanwhile I've been eyeballing the 1 micron filters I use in my RO water filter setup. I have all the other parts including a powerful little elect pump. Now for the next few few days part of my brain will be trying to talk the rest of it into making said setup. It's also telling me to find some kind of filter material to put around my MB filter. Not the whole thing obviously, but like a 1" ring around it or maybe just a square patch. So >99% of the oil would take the easier path via the main filter but it would slowly catch stuff...
As you can see I spend way too much time thinking about stuff that very few others care about...

Thank you for all your valuable experience and innovations. I will definitely try your blend of Lucas. Your Amsoil suggestion is terrific: the Euro 5w-40 has thicker specs than the Mobil 1 Euro 0w-40 I've been using. I'll look into using a magnet. I love the way your mind works . . . keep going! Thank you, thank you!