Oil for MB with *warm* start knock issue

sds

Messages
18
Location
MA
Purchased a garage queen 2009 CLK550 with 60K miles. Car is in pristine condition, but I realized it suffers from the often hard-to-replicate warm start knock issue that plagues some M272 V6s and M273 V8s.

If the car is up to temp, turned off, and then turned on again around 45 minutes to 2 hours later, it exhibits a 1.5-2 second knock from the bottom end. It does not occur on a cold or very hot start.

My understanding is that MB specced a few bearing clearance(s) too loose and that most folks ignore the issue and live with it. My understanding is that dealerships also tell people to live with it.

The “true” solution is to change the bearings to get a tighter tolerance, but that’s not an option here (ideally). Its not cost effective, and I’m generally averse to opening up a motor. I also do want the motor to last a long time because it’s a cream puff example of the car, and it’s (in my opinion) an underrated vehicle that I’d like to keep for a while.

I’m noticing the issue a bit more often after my first oil change with Castrol Edge 0W40. Would a slightly thicker oil help here? My guess is that the problem rears its head during the time when the oil is still warm (thinner), but the oil has left the bearings/channels and has collected back into the sump.

If helpful, it sounds identical to this:
 

OVERKILL

$100 Site Donor 2021
Messages
46,487
Location
Ontario, Canada
If the oil was too thin/clearance too wide, it wouldn't stop knocking after a couple seconds and it would get worse with the engine hot. Sounds more like something that bleeds down and takes a second or two to pump back up and this isn't as pronounced on a cold start, possibly due to cold start logic operating the engine differently.
 
Messages
2,393
Location
Paradise of Florida
Try a run with Ford 5w50 or BMW 10w60. Might even want to give a 15w40 like Delvac1 or RotellaT6 a test(much more HTHS than a 0w40).

If low on oil, test viscosity with a bottle of oil thickening snake oil before the next OCI. STP synthetic or BG MOA are both easy enough to source.

Also can be caused by filter flow restriction.... what oil filter?

What oil change interval history?

Should also research whether the filter mount or engine block has some ADBV or BPV, if any, and test those components.

Sounds like normal engine wear... caused by blind trust in the auto manufacturer's oil and change interval recommendations. True solution??? doubt it because it'll simply wear out again.
 
Messages
2,207
Location
Muncie, Indiana
If the oil was too thin/clearance too wide, it wouldn't stop knocking after a couple seconds and it would get worse with the engine hot. Sounds more like something that bleeds down and takes a second or two to pump back up and this isn't as pronounced on a cold start, possibly due to cold start logic operating the engine differently.
I think the idea is that the bearing clearances are too wide and when the oil is already warmed up and you restart the car it leaks out from the bearings at a greater rate than at a true cold start so it takes longer for the pressure to build in the bearings compared to at a cold start where the oil is much thicker and doesn't drain from the bearing nearly as quickly causing the noticeable knock for a few seconds on a warm start but not at a cold start..
 
Messages
16,496
Location
N.H, U.S.A.
Reads like a worn bearing or a TC slap; I didnt watch your video. I highly doubt MB spec'd main or rod bearings too loose.
2 seconds isnt anything to worry about with no load. You can also have issue with carbon and mineral crust on the piston tops and head in the quench area. Get that thing out and "give it the beans" now and then ; a good Ronin Flogging.

I fear we will all be having bearing issue too soon with the advent of stop start systems if you don't hit that "defeat" button after every start.
 

Astro14

$100 Site Donor
Staff member
Messages
13,370
Location
Virginia Beach
That’s a horrible sound. I’ve never had a car with decent bearings do that. Even after an oil change, when all the oil has, presumably, drained off.

I would replace the bearings, but if you’re looking for an oil solution to try and stop, or at least mitigate, this, I think I would go with the Castrol10W60.
 

OVERKILL

$100 Site Donor 2021
Messages
46,487
Location
Ontario, Canada
I think the idea is that the bearing clearances are too wide and when the oil is already warmed up and you restart the car it leaks out from the bearings at a greater rate than at a true cold start so it takes longer for the pressure to build in the bearings compared to at a cold start where the oil is much thicker and doesn't drain from the bearing nearly as quickly causing the noticeable knock for a few seconds on a warm start but not at a cold start..

I hear you, but I just don't see it. With warm oil and a positive displacement pump (the whole lube system doesn't go dry) the leakage is in no way going to overwhelm the displacement from the oil pump, particularly with warm oil where the relief isn't coming into play. If it did, you'd never be able to establish oil pressure. If this was excessive bearing clearance, it would make noise on a cold start until oil pressure was established too as that bearing would just be on residual film for those first couple seconds.

If you've ever owned an engine with rod bearings that have enough excessive clearance to knock, it isn't a noise that goes away after a couple of seconds, it gets louder the thinner the oil gets, but can be dead quiet after receiving pressure on a cold start due to there being sufficient viscosity in the bearings to quiet it. An acquaintance of mine had an old 302 that was really worn out and it would knock for a couple seconds cold then get quiet, then come back and get progressively louder as the oil thinned until it sounded like a diesel at hot idle :ROFLMAO:

The oil pump doesn't pressurize/jack up the bearings, it simply provides pressurized supply at the feed orifices and they self-draw. @Shannow has written extensively on how this functions in the past. HTHS is quite literally the viscosity the bearings see, so if that viscosity is inadequate, it's inadequate, it doesn't improve after 2 seconds, which is where I'm getting hung-up on with this. It sounds more like a tensioner or something hydraulically activated that takes a couple seconds to come back up.

I may go looking for a diagram of this engine if I get a few minutes, see if I can find out, as this has piqued my interest.
 

OVERKILL

$100 Site Donor 2021
Messages
46,487
Location
Ontario, Canada
Apparently the timing chain gear on this engine is prone to failure?
Fault Code Scenario 1: DTC 1200 and/or 1208 is/are present in ME-SFI control module. The fault codes are recorded as current and/or stored in the fault memory. When the fault memory is erased and the engine is restarted, the fault codes reoccur immediately. This is due to the positioning of the timing chain driven camshafts relative to the crankshaft and can be caused by a worn sprocket on the balance shaft on engine M272 or by a worn guide (idler) gear for the timing chain on engine M273. Figure 1, 2 and 3 show extremely worn sprocket gears. Figure 4, for comparison, shows a new sprocket gear.

Screen Shot 2021-05-10 at 9.45.48 AM.jpg


Also from that TSB, looks like the camshaft adjustment solenoid is right on the front of the engine:
Screen Shot 2021-05-10 at 9.46.41 AM.jpg


Interesting.... 🤷‍♂️
 
Messages
11,168
Location
MA
Haven't heard that on my 2 M272 engines. Only problem with those oils that others mentioned is that they're not MB 229.5. But maybe you can get away with it if you don't do the 10k oil changes. The timing chain problem basically affected the 2006/2007 models so I think by 2009, it should be out of range for that particular problem. Could still be a problem with the timing chain though, just not caused by that particular problem. You can check the serial number of the engine by using this vin decoder and see what it says on the engine number. I'm pretty sure it's well out of range.


Your other issues with this motor is going to be the oil separator/breather cover, causes the intake manifold to go when oil gums up the flaps. The 3 plugs in the back might also leak oil, I'd check those too.
 

sds

Thread starter
Messages
18
Location
MA
Apparently the timing chain gear on this engine is prone to failure?


View attachment 56702

Also from that TSB, looks like the camshaft adjustment solenoid is right on the front of the engine:
View attachment 56703

Interesting.... 🤷‍♂️

So I made sure to buy a car that was out of the VIN range for this issue. But I do think it’s related to this thread here.



The explanation is:
“The knocking sound is from the upper main bearings, theres not enough oil pressure built up during the first couple seconds of startup. The fix is to remove the old bearings and replace them with one size bigger bearings to help build pressure as soon as the engine starts.”

The M272 V6 and M273 V8 are the same design (broadly) and share bearings...
 
Messages
35,944
Location
NY
Maybe install a pre-lube system. Short of using straight 70 weight, no oil is going to fix that noise.
That might be helpful. Having said that I know a few people with what sounds like the same problem, and the engines ran for as long as they owned the vehicles. Something like Schaeffer's #132 might put a band-aid on the problem, and reduce or hide the noise.
 

OVERKILL

$100 Site Donor 2021
Messages
46,487
Location
Ontario, Canada
So I made sure to buy a car that was out of the VIN range for this issue. But I do think it’s related to this thread here.



The explanation is:
“The knocking sound is from the upper main bearings, theres not enough oil pressure built up during the first couple seconds of startup. The fix is to remove the old bearings and replace them with one size bigger bearings to help build pressure as soon as the engine starts.”

The M272 V6 and M273 V8 are the same design (broadly) and share bearings...

I'm not comfortable with that explanation (main bearings), due to the reasons I already mentioned, they should make noise with the engine hot if it was a clearance issue. If you shut it off, wait 10 minutes so the oil stays hot (at its thinnest) and re-start, does it make noise? If not, then you can dump the thin oil theory, as if the engine has been sitting two hours, the oil is going to be considerably cooler (and thicker) than it would be after a shorter period. Of course when you let the engine completely cool, the oil is even heavier, but cold start high idle logic will be different from warm idle start and that higher RPM may be the reason you don't hear noise.

I'm not saying it's impossible to be the main bearings, but it's not likely based on the description of the issue.

Also, the issue mentioned in that first link appears to be different from your issue:
We leased a C300 two weeks ago. Has about 450 miles on it. Since it was new, it has a cold start noise that is troubling. Like it's low on oil. Not really a tappet noise though, more like a bearing noise. Noise sounds "throatier". Goes away in about 3-5 seconds. Only happens in the morning after she sits overnight. Oil level is correct. No other symptoms. We are south Texas so it is hot. Garage gets over 100 degrees regularly. Could it be the timing chain?

As that one makes the noise on a cold start, while you are saying yours makes noise on a warm start.
 

OVERKILL

$100 Site Donor 2021
Messages
46,487
Location
Ontario, Canada
So I made sure to buy a car that was out of the VIN range for this issue. But I do think it’s related to this thread here.



The explanation is:
“The knocking sound is from the upper main bearings, theres not enough oil pressure built up during the first couple seconds of startup. The fix is to remove the old bearings and replace them with one size bigger bearings to help build pressure as soon as the engine starts.”

The M272 V6 and M273 V8 are the same design (broadly) and share bearings...

Wow, that other thread is wild!

Multiple different issues, some folks had cold start knock, a couple of them had the same as you (warm start knock) and two people had their main bearings (and who knows what else) replaced but their noise was getting worse. One guy had his timing chain guides replaced, but his noise seemed to last longer (5-10 seconds) and it seems most people just live with it if it doesn't get worse. Another guy had his oil pump replaced due to low oil pressure (which didn't help, this DOES point to worn bearings) and the one guy that had his bearings replaced had another Merc that made the same noise but it self-rectified :ROFLMAO: Somebody asked him to provide a list of what was actually replaced, but he never got back on that.

So, it seems that going through the process can indeed result in the noise being eliminated. Depending on the cost, if it isn't getting worse, it might make sense to just keep an ear on it. On the other hand, if it is driving you nuts, it sounds like going through the process of getting the mains replaced has yielded some success for those who have followed-through with having it performed so it may make sense to do so. No wizard in a can is going to help (and that was covered in the thread, heavier oil did NOT improve things) so either live with it for now or get the work done.
 
Last edited:

sds

Thread starter
Messages
18
Location
MA
I might just drive it and keep note of it. I don’t think an engine-out main bearing replacement is the right move value-wise.

Scoured eBay just now and found a few sub 60K mile M273 longblocks for ~$2000. Worst case scenario (if the crank is ruined), I could go that route.

(Might even buy one and store it...I really do love this car. Pillarless coupe with a big V8 in a small chassis.)
 

OVERKILL

$100 Site Donor 2021
Messages
46,487
Location
Ontario, Canada
I might just drive it and keep note of it. I don’t think an engine-out main bearing replacement is the right move value-wise.

Scoured eBay just now and found a few sub 60K mile M273 longblocks for ~$2000. Worst case scenario (if the crank is ruined), I could go that route.

(Might even buy one and store it...I really do love this car. Pillarless coupe with a big V8 in a small chassis.)

Sounds like the most logical course of action.
 
Messages
11,168
Location
MA
I might just drive it and keep note of it. I don’t think an engine-out main bearing replacement is the right move value-wise.

Scoured eBay just now and found a few sub 60K mile M273 longblocks for ~$2000. Worst case scenario (if the crank is ruined), I could go that route.

(Might even buy one and store it...I really do love this car. Pillarless coupe with a big V8 in a small chassis.)
Price always go down over time but I suppose it will reach a point where they will start to go up again. Plus all it takes is one idiot on the road to smash your ride. Probably premature to buy an engine although I suppose you could always turn it into a table stand.
 
Top