samdunlap

...boy, was that a mistake!
My name is Sam and I live in Klamath Falls Oregon. I'm new to Mercedes but always wanted one so when I found a 2002 ML320 in Longview, WA, owned by a widow-lady too old to safely drive anymore, I couldn't get there fast enough. It is black, beautiful and like new with 135,000 miles. She hadn't driven much in the past five years so the soft tapping sound I heard, when I test-drove it, didn't concern me much. After all, she had just replaced four catalytic converters, at a ridiculous cost, so I concluded that it was a lifter that was not up to pressure, but as I proudly zoomed around, the tapping became louder.
After about a month, I sought the advice of an independent foreign car mechanic. After listening to the engine, and my story, he suggested adding Rislone until my appointment date two weeks later. He spent a couple days ruling out things like the timing chain, cam followers and everything else but piston slap. He finally asked if I would let him pull the thing out and flip it over for a peek. I agreed.
The cylinder walls were scored along the left bank where the tapping was heard. Along the right bank were the beginnings of scarring too.
Fast-forward to today. I have a beautiful ML320 in my driveway and an engine, that by all accounts has been very well cared for, sitting at my mechanic's shop waiting to hear its fate.
Originally, I found MBWorld while I was trying to determine what the tapping could be but now I've joined the forum to ask your advice.
In your opinion, what should I do? Rebuild it, get a remanufactured one, pick-up a used engine, or scrap the while thing?
Thanks,
Sam

DrX

Did this soft tapping sound occur at a constant frequency, or did it vary with engine speed?

samdunlap

Unlike others, where the tapping goes away as the temperature increases, mine is present always and varies with the speed of the engine. We've pulled it out of the vehicle for a look inside and see scoring in the cylinder walls.
it's looking like a rebuild or replacement is inevitable.
Sam

DrX

If the engine runs fine with just a tapping noise, replacing the whole engine sounds totally unnecessary.

I think you should reassemble the engine and change the oil for Mobil 1 0W-40. Install a Mann or genuine MB polyester fleece filter.

If the tapping doesn't resolve after a month or two, replace the left bank lifters.

samdunlap

I'm on board with your thinking but I ran it for a month with Mobil 1 5W-40 and a Mann filter. If anything, the tapping may have gotten louder. You're suggesting that lifters are the source of my problem, but if that's the case, how do I resolve the scoring on the cylinder walls?
Thanks, Sam

DrX

I can't imagine how scoring on the cylinder walls would cause a tapping noise. Anyway, for a car with low mileage driven by a little old lady who had all her servicing done at the MB dealer, it doesn't sound like it's of any consequence. Engine runs fine. Where's a pic of this so-called scoring? Have you actually seen it?

Brand new lifters from MB cost $14/$22, need 3 per cylinder, so 9 in total. Reconditioned engine will set you back a lot more than $174.

Your description of the sound is a bit vague. It might be simply your purge valve, that sits in a bracket attached to the firewall. It makes a tapping noise heard loudest behind the left side of the dashboard. My mechanic caused mine to get loud after a service visit - to resolve, they put a block of foam between it and the bracket.

samdunlap

Unfortunately, I have seen the scoring on the cylinder walls and it coincides with the loudest tapping. Using a stethoscope, I was able to isolate it to cylinder #1, then once the engine was out, the majority of scoring was on the wall of the same cylinder. I didn't take a picture but the scoring was most evident beginning at #1 then lessening along the others. There was only a small amount of scoring on the right bank walls.
My mechanic has a theory that makes sense. The oil had last been changed at a quick lube. The sticker indicated that Mobil 1 was used but the quality of the filter wasn't indicated. He believes that the filter may have been a cheapo that disintegrated under pressure thus clogging the small tubing that oils the cylinder walls. Whatever happened was quick because the engine components are like new inside. An example is the timing chain and sprocket are in new condition.
I don't know if this is the cause but the theory seems plausible. Whatever the case, it sounds like a diesel and that's not OK.
Thank you for your help.
Sam.

DrX

Thanks.

If the noise comes from cylinder #1, then it's on the right bank and the opposite side/corner of the engine from the purge valve. Left/right is determined by you sitting in the driver's seat facing the direction of travel, not you standing in front of the open hood looking at the engine.

Anyway, a blocked oil gallery could deprive the cylinder #1 lifters of oil as well as the walls. If it was mine, I'd replace the 3 lifters for $58 and put it back together. Put in 0W-40, not 5W-40 which is thicker at cold start.

samdunlap

Somehow I got it in my head that cylinder number one is on the driver's side front. The loudest tapping came from cylinder number four.
Your thinking appeals to me for the economy but also to avoid buying a used engine with problems of its own. It never occurred to me that the lifters are supplied with oil from the lines that oil the cylinder walls. I will talk to my mechanic about clearing or replacing the oil lines and then lifters if necessary. The downside would be going through the work of reinstalling the repaired engine only to have the tapping continue.
Thanks,
Sam