My mother replaced 6 injectors for a knocking symptom recently. (yes I warned her about the "new" injectors. The mechanic replaced it and knocking symptoms remained. Possible bad new injector, but that was switched and knocking remained. Compression test revealed about 275 on cyl. 3. Leak down results showed normal leakage on valves and pressure HOLDING in the cylinder. So, if no air escapes out of the valves or through the rings but the compression is low, the mechanic assumes a possible bent rod. Admittedly very rare. Low mileage 603 at 100,000.
To help my mother, i may remove the head. Tow to the mechanic after that.

Based on these symptoms, would you agree with bent rod?

Thanks everyone.

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63 220S W111
76 300D W115
2013 VW JSW TDI M6

previously-
73 280 SEL 4.5
86 300E 5 speed
2010 VW Jetta TDI M6

I'm just grasping at straws here but, traditionally, the bent rods in the 350 engines do not result in any "knocking" noises. They simply ovalize the cylinder until the oil consumption climbes dramatically.

There needs to be some correlation between the "knock" and a bent rod before I would head off in that direction.

Furthermore, if the rod was bent, the cylinder would begin to wear unevenly and a leakdown test would reflect this. Of course, I am assuming that the rod didn't bend yesterday.

Did the knock start without warning or did it come on slowly?

If you remove the head just measure piston height for each cylinder. It will tell you if you have a bent rod or rods.
Good luck

It could be fuel pump delivery seals.

Check Post #7 of this search, and try others.

Some progress was made today!

Best Regards,
Jim

Thanks for the replies. Jim H, it has been in fact determined that one cylinder has low compression, so delivery seals could be a separate issue I suppose.
Brian, I had been pondering this and may have identified the point at which this occured. Around Christmas, my mother took a 4 hour road trip to the northern part of California. Besides that, she doesnt drive a whole lot. She called me frantically from the road complaining of a huge cloud of white smoke that billowed from the car while ascending a large hill (highway speeds). The smoking ceased, but from that point on she complained of knocking sounds and lots of white smoke in the morning after startup. It has been cold so the mechanic considered this to be merely condensation.
Now I'm thinking maybe a minute crack developed in the head, spraying coolant into cyl. 3 and causing hydrolock. There isn't any pressure or oil in the coolant so it is hard to say. I'm not an expert by any means.

I'm going to order the CD rom from mercedes for the sdl and attempt to remove the head for her. I've R&R the head on an M117 and just rebuilt the front end of my 115 but I will be relying on y'al for help.
One thing I know is to not loose the damn timing on the IP!!

Thanks for reading and any help offered is welcome.

By the way, it isnt a 350SDL, just an 86 300SDL

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63 220S W111
76 300D W115
2013 VW JSW TDI M6

previously-
73 280 SEL 4.5
86 300E 5 speed
2010 VW Jetta TDI M6

joshhol I am confused are you talking about a 300SDL or a 350SDL?

The 300SDL used the 3L 603, these are very good engines that do not bend rods. I have never heard of a 3L 603 bending a rod.

Sounds like the head gasket could have blown.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200

I'm the one who confused the issue, Hattie. For some reason, I was thinking the 350 engine. Now that it is confirmed to be the standard 3 litre engine, it is very unlikely that a rod has bent, as Hattie has mentioned.

Far more likely that it blew the head gasket with the evidence of a cloud of white smoke. You also might find some cracks there, as you know.

I'm sorry, I didn't know a 350SDL was also a 603, but then again I probably did know that but didn't think to clarify it right off.

It is an 86 300SDL. I need to do more research, on this forum and I need to see if it is a #14 head. I don't know, nor do I know where to look on the head to figure this out.

In reading gsxr's post here (page 2): The #14 head on the 603, really bad? For sure?

it doesn't sound like a blown head gasket. I'm thinking bent rod as a result of a crack in the head. Yes a bent rod is rare in a 300SDL. My mechanic, who was learning on the 108's when they were new said he's only seen three 300SDL's with bent rods.

Now, I had a sickening feeling as to the possible cause of this crack. My mother had the begginings of a leaky radiator in October. My mechanic gave me a good used one and I put it in. What if I didn't get all the air out of the system allowing pockets of steam to form in the upper passages? It never ran hot. It didn't seem all that hard to refill the rad when I did it. Was it "too easy"? Meaning is the air Really tough to get out of the system?

Thanks

__________________
63 220S W111
76 300D W115
2013 VW JSW TDI M6

previously-
73 280 SEL 4.5
86 300E 5 speed
2010 VW Jetta TDI M6

Well I put my money on a blown head gasket and/or cracked head. With that low of mileage though I wouldn't expect either so soon!!! Your wanting to pull the head sounds like the thing to do at this point. MB mechanic who owns a 601 and a 603 said the 603 is common to have head cracks and blown head gaskets. The 601 he says only needs head gaskets after a certain time no matter the mileage... I don't know about that. I think he just wants me to give him my money prematurely.
A bent rod seems way too extreme for this engine. A head gasket and head are bad enough!


Question for all:
What are the life expectancies of heads and head gaskets for all OM6XX??

__________________
1984 190D 2.2 Auto 220k
2001 Jeep Cherokee Sport 70K
2004 Lexus RX-330 ??K
2005 Chrylser Crossfire LTD 6K

Play guitar? Go to www.cyberfret.com for free online lessons!

617's are only good for 300-400K. After that you need to spend $200-300 on a new gasket and a valve regrind

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

Some 603 head gaskets last a long time others blow young. Mine is still going strong. I would pull the head and see what you find.

__________________
2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200

The 601 story is bogus. Certain early 601's had inferior head gaskets, and they would tend to leak between the timing chain area and the first cylinder (from the oil passage. The later head gaskets solved this issue.

My 601 leak started with about 150kmi (it was very minor, and did not relate to compression). I replaced it at about 212kmi and never had a problem again (11 years later with 397kmi).

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Jovan

'84 (11/83) 190D 2.2 5-Speed; Silver/Blue; Motor No. 00354, 402k mi (340+kmi mine)

'89 Porsche 911 Turbo Coupe; Black/Black; 53kmi
'05 BMW 530i 6-Speed; 302kmi
'19 Range Rover; 30kmi

Yeah I know those 300-400K mile head gasket charges are a real anoyance.....Particularly with all these Million mile benzes being sold on ebay all the time............... bwaaaahahahaha

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Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

Wait, I thought they went 2 million miles? After all, they're MB diesels!

dAVID

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2000 Honda Accord V6 137k miles

1972 300SEL 4.5 98k miles

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What is better, the service CD rom or a factory paper manual for 603 engines?

I'm sure most would say the CD but I wonder if they leave things out. Also, I would rather have a book in my hands while in the garage rather than having to come inside with grease all over and deal with a stupid computer that errors often enough and no printout to take back outside.

No photographic memory here.

That being said, a cd rom has Everything on the car, for about the same as just an engine manual.

Thanks

__________________
63 220S W111
76 300D W115
2013 VW JSW TDI M6

previously-
73 280 SEL 4.5
86 300E 5 speed
2010 VW Jetta TDI M6