HIS

SL500 2003. Engine no 113.963

I have a loud knocking sound when starting a cold engine. Lasts about 10-15 seconds and then this sound disappear. It comes from the left valve cover. The sound follows the engine speed and agrees that it knocks half the crankshaft speed. There is certainly something about the camshaft or rocker arms, valve lifters.
My question is does anyone know this problem and what was the fault on your engine?

MarkCan

Will the problem reoccur when you turn the engine off and restart?

Rudeney

Probably a bad lifter. Since it goes away when it warms up, it may just have some sludge in it. In that case, running the engine hard with a thin weight oil can help. What oil do you use?

Leej

It might be a lifter going bad that quiets down once the oil flowing as @Rudeney suggests (I have found his advice to always be spot on). How many miles are on it?

We have a 2004 Lexus LX470 (190K miles, V8 gasoline) that makes a clacking noise for the first 10 seconds on a cold engine, and I assumed it was a lifter. It has done this for the past 3 years and seems a little worse (lasts longer) in the winter and less noticeable in the summer. The research on the Lexus/Toyota forums indicated that it was "piston slap" and is a common (normal) issue with older Lexus/Toyota V8 (UZJ100) engines, and to just drive it and not worry about it unless it got worse (louder or lasted longer). However, we also have a 2000 Toyota Landcruiser 160K miles (identical to the Lexus LX470 but with fewer miles), and it does NOT exhibit this behavior (yet?). I don't know if this is common in Mercedes or not, I not aware of it. But you might do some searching for piston slap.

In either case, @Rudeney 's advice of thinner oil might help.

Lee

SLcharge

Add a can of this, and it will clean the lifter's oil passages.
It's no snake oil, it works, if it's a lifter though.

HIS

Thanks for all suggestions.

The car has now 71000 mi. I don't drive much, aprox 2000 mi/year. Talking about oil I usually use Mobile 10W-30 synthetic oil. But have also tried different brand.

What oil quality do you use your cars?

SLcharge

I use Mobil 1 ESP 5W30, service interval 15k km.
My engine has now 216K km on the odo, and still use no oil.

sean65

Is it possible that the knocking is from the belt tensioner which I believe is also oil pressure driven. If the oil pressure is low until warmed up, it could conceivably cause a knocking. Then again I may be confusing it with my old SLK350.

SLcharge

The belt tensioner is spring loaded. The chain tensioner is oil pressure loaded.
But I don't see how the chain or it's driven components could create a knocking sound ?

sean65

Got it, and you're right, chain tensioner. I believe the theory is that at start up, until oil pressure builds, the tensioner can bounce a bit causing a knock. I never had it with the SL, but I want to say that my SLK exhibited that behavior occasionally.

SLcharge

Hmmm. Weird.
Severe slag in the chain, and it hitting the engine block or chain cover housing, could explain it, but normally less slag sounds like a rattle, not like knocking.
If you are right, the chain tensioner should be changed, it's a known issue on the M272/273 engine, not that much on the M113 engine.
My money is still on a clogged up lifter.

Rudeney

I use Mobil 0w40 because it's on the approved 229.5 list and readily available (about $26 for a 5qt jug at Walmart).

The chain tensioner on the MM12/M113 engines is hydraulic, so this could get noisy. Replacement is fairly simple - just remover engine covers and the alternator for access. Torque is 80Nm.

SLcharge

[QUOTE=Rudeney;7952321
The chain tensioner on the MM12/M113 engines is hydraulic, so this could get noisy. Replacement is fairly simple - just remover engine covers and the alternator for access. Torque is 80Nm.[/QUOTE]

Rodney, think about it, knocking from the chain, I doubt it, but on the other hand, sound is deceptive. What is knocking to one person is ticking to the other, and wise versa.

By the way, Mobil 1 ESP 5W30 have the following approvals.
MB-Approval 229.31
MB-Approval 229.51
MB-Approval 229.52

HIS

Well for me it very clear the sound is knocking and nothing else. It can also be heard that it is just one lifter or rocking arm knocking.

I will try the thin Mobil 0w40 oil and perhaps also add one can of additive. This should be interesting to hear the result.

Thanks for now

Rudeney

Yes, it makes much more sense that the sound is a lifter (a not uncommon problem on the M112/M113 engines). A bad timing chain tensioner might still make noise, but probably not a paced knocking sound.