Hi all,

I'm new to this forum. Great information on here!

I probably know the answer before I even ask the question (do an engine swap), but I thought I'd ask anyway. I have a 1984 300SD with the original engine, which has never been overhauled. Highway car all its life, and still looks awesome. I had a valve job done (broken valve guide was causing all kinds of problems) at 703K miles. Ran great for about 20K, and it started acting up again. Right now, I have a really rough (and blue-smokey) idle. Once you get it running down the road, it still runs like a champ. But at idle, it's smoking, running rough, just really carrying on. The exhaust smells to me like raw fuel. I have a perfect spare engine. Today, I switched injectors. No noticeable difference (I was hoping it was just a sticky injector).

The main thing that concerned me when I changed out the injectors was that there was engine oil on the end of both the front two injectors. A little bit on the rear injector, and the other two, 3 & 4, were pretty much dry. Would that be a sign of rings letting oil past? Like I said, I'm no mechanic. Just an ignorant guy asking more knowledgeable folks!

I've been driving these old MB diesels for many years, but I'm no mechanic. I can do parts swaps, etc., not a complete idiot, but not an expert either. Just wondering if anyone has any ideas on this. I want to keep this old engine alive as long as possible. That was the goal when I bought it. Is it time to give up the ghost and accept the fact that she needs an overhaul (or engine swap in my case), or do you think there's a chance to keep her going?

Any input will be greatly appreciated. Thank you!

Welcome to the forum ...

I would start with: 1) a valve adjustment and 2) a compression test. Even with the high mileage, no sense giving up on it before getting some data. A valve adjustment can make a pretty big difference if the clearances were way off. And compression numbers will tell you a lot.
Any trouble starting? Does it burn oil?

__________________
1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)

Thanks much. Like I said, it's been about 25K miles since the valve job. The man who did that work is very respected amongst owners of these older MB cars in this area. He did a compression test then, and said that although the compression was a little low on all five cylinders, some worse than others, it wasn't as low as he'd have expected, given the mileage. He seemed to think the old engine still had a good deal of life left in it at the time. The valve adjustment (naturally) was done at the same time, but I haven't had it done since. I guess it's certainly due. I'm going to give him a call this week, and see if I can get it done. Sure can't hurt....

If you're going to see the mechanic anyway I'd ask him to do have a look at the problem.

He might agree to do a leak down test to get a better idea of where to problem lies.

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

That's some massively high mileage, impressive, how many miles have you put on the car? I'm no expert either, but if the valves were resealed, it could be now putting more pressure on the rings.

you are way overdue for a valve adjustment. Such adjustments are scheduled for 15k miles on your engine. I would do that first, then look for improvement.

If no improvement, a leak-down test would be in order for the reasons given above.

Please keep us up to speed. Most on this forum are interested in the OM617 aging process.

750KMILZ, you aren't by any chance the guy they did a news profile on, are you? Some guy in NC, bought an SD with 580k on it, now over 700k. Amazing to think that there may be SEVERAL of these out there!

__________________
14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

The oil found on the injectors could be blow by, take the hose off the valve cover or remove the oil cap at idle, is there lots of pressure? If so bingo, could be rings, could be valves, could be timing but yes internal NOT injection pump issues. For example the oil cap should stay put once unthreaded, not fly off from pressure. If there is not a ton of blowby look at the injection system, maybe chain timing, start of injection timing, lack of pressure. A good pump recalibration costs money but really can refresh performance on an older engine, it was night and day on two of our cars (that had everything else checked out).
I would figure it out before swapping engines, then you know what parts are good in the future even if you decide to swap in the end. Compression does not tell much of the story, sure it can tell you when it is worn out (a drive will usually tell you that, or hard to start!) but little else. The timing and pressure of the injection pump is probably a key here.
Possibly the cam timing could be off since the head work too...thinking aloud maybe the keyway is drifting (seen it on VWs often after work). Chain could be too loose and skipped time, of course at this age and mileage it could be anything!

Realistically an engine with 728k miles on it is extremely due for a full overhaul in every way....its probably not worth putting a lot of work/$$ into that engine unless you want to fully rebuild.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

My Qs too.......as well as my shared initial suspicion surrounding the symptoms of probably cause as described.

I would want a redo on the compression check, with readings provided in writing to refer to.

Time to find another engine bro.

Put that one on the stand and tear it down and let us know what you find. Were the same valves put back in it during the guide job? I'd look for worn out rings or bad piston.

I have also heard of this happening where you go through the top end and the bottom end dies shortly thereafter.

__________________
Jim

I think I can speak with some knowledge on high mileage 617's.
it is hardly worth the effort to rebuild. Every moving part will be worn. Best replace the motor. You can pull the old motor down for fun if you wish.
What is the trans like? At that mileage it is probably beyond being rebuilt.
Diff is probably very loose.

__________________
Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

It happened to my friends 240d, he was really upset because it developed a bad head gasket shortly after he bought it....had a local merc guy redo the head and gasket.....but the bottom end couldn't handle the increased compression so a bearing went bad...

If you have the cash buy a rebuilt engine, will promise it will last the rest of your life and its cheaper then a new car....if your on a budget find a good used lower milage one...

Raises a question, can one still buy a new engine through the dealer?

__________________

I would adjust the valves and check compression before condemning the engine. How bad is it smoking? How much oil does it use? I'm guessing there's a little life left in it, but after over 700,000 miles, I wouldn't expect much.

__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

Raises a question, can one still buy a new engine through the dealer?[/QUOTE]

I asked my local dealer this for a bit of fun...

Australian prices, $19,500 for an engine and $7,500 for a transmission

__________________
1995 E300 Diesel