I will preface this by saying I am a complete idiot.

I have a 1985 300CD that, after an odd turn of events, turned from a superb runner to an asthmatic dog. The last time it was running great was yesterday, after I successfully finished a valve adjustment. I did the procedure by the book and it turned out great. So smooth! I took it for a nice long test drive to enjoy the fruits of my labor.

Later that day, I was headed out to visit some friends about 2.5 hours away. The 300CD had been on the highway before, and after the valve adjustment, I was feeling confident about the performance I could expect. While still on the city roads, I noticed that if I braked, the engine would shudder slowly from left to right. I remembered this phenomenon happening just after I bought the car last month, and it went away after I did an oil and filter change. Figuring this could be cured before I left on my trip, I pulled into AutoZone to check my oil level. This is where it begins:

Pit-stop 1: Stopped at Autozone and checked my oil level, which was about halfway between the full and low marks. Went in to get some Delo to top it off. I was careful not to put too much in, checking the oil level as I went. Job done, I cleaned up and went on my way. Three miles or so down the road, I know something's not right. The engine is rocking a bit more at idle, so I pull over at the next gas station to see what's up.

Pit-stop 2: I check my oil level again, and I feel like an idiot. The level is about a quarter of an inch (maybe a bit less) above the full mark. I decide it's not a good idea to keep on driving like this, so I pull out my 13mm wrench and oil drip pan and figure I'll drain the excess and fill up as needed. This doesn't go exactly to plan, as the drain plug is pretty hard to replace with hot oil gushing out. I end up draining more than I wanted to, but I don't panic because it's in the drip pan. Eventually I replace the drain plug, pull my drip pan from under the car and refill to the precise level, waiting and checking several times to make sure it's right this time. I let the engine idle for a few minutes and resume my journey. The shaking I experienced at overfull is now gone.

Before long, I pull on to the highway, and it doesn't take long for me to know there's a problem. The engine is knocking and making a light, airy whirring noise. Power is way down, and I need to really put the pedal down just to go 50 mph. I pull over at the next offramp and see what's going on.

Pit-stop 3: I check the oil level, which is still perfect, exactly at full. I check closely for leaks; there are none. I don't see anything that's obviously wrong, and the engine runs fine unless I'm accelerating or at highway speed. I decide to pack it in and drive the merc carefully home.

There are a few possibilities that have crossed my mind:

Oil contamination: My drip pan is a sealed one with the lid that screws on top. I bought it brand new, and used it previously to drain a lawn mower and a Toyota Corolla, and I disposed of the oil afterwards. The last time I used it was for my last 300CD oil change; the oil was drained while hot and discarded before it had a chance to cool, theoretically dissolving much of the reside from the other oils that might be there. Thinner oils for a diesel are not good, but if there's any in there, it's in trace amounts.

Metal contamination: In theory, metal shavings from the bottom of the oil pan might more easily find their way into critical components when the same oil is re-filled. But really? The OM617 has a (new) oil filter that should take care of that

Mechanical damage: Either from excess oil or from the shaking it caused

Fouled injectors and/or glow plugs: Excess oil might have fouled these, leading to incomplete combustion, causing the power decrease and strange noise

Sorry for the long read, but I can't quite wrap my head around this one. It pains me to consider things like scored piston rings or valve damage, but either way, I love this 300CD and I'm not giving up on it.

I would re-check your valve adjustments. Or look for damage to hoses while doing the valve job. The oil troubles don't seem related unles you filled it with water in the oil. You would see that on the dipstick.

Possibility 5: The problem is totally unrelated to the oil.
Check your alda/overboost protection circuit beginning with the banjo bolt on the back of the intake manifold. Sounds to me as if that pressure line is disconnected. (you damaged or disconnected the line while removing the valve cover--the problem is common since the plastic in the line gets hard and brittle)

And no, you're not a complete idiot. The open discussion is reserved for posts by us complete idiots.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

I'd be more inclined to hypothesize something wasn't done right with the valve adjustment before speculating about internal engine damage.

Check the line from the ALDA banjo on back. I induced similar symptoms by forgetting to snug down the banjo bolt on the back of the intake manifold. Nice smooth idle, asthmatic wheezy noises and no power on the highway.

You may have set one of your valves to the wrong position: intake for exhaust or vice versa, that would also be something to check.

A regular, not-on-the-side-of-the-road oil change might also be prudent. It is possible that you put something that had settled in the pan back into the engine but if it's smooth (more or less) at idle I wouldn't immediately speculate catastrophe.

I'm guessing it's not oil related. Rough running and lack of power sounds to me like fuel filters. Maybe run a can or two of Diesel Purge then change the filters. Also check your air filter.

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Agree with Kerry. Sounds like you pulled off the plastic line to the switchover valve. Did that to mine (300SD) and could not get over 50 mph. Looked under the hood, stuck the line back on, and instantly proper amount of power.

Thanks, everyone for posting so far! Heart attack averted now that engine damage doesn't seem like the likely culprit.

Improper valve adjustment would be my first suspicion as well, were it not for three things. First, I used a printed diagram to track my progress, checking and rechecking and rechecking proper clearances and sorting out intake/exhaust. Second, I tightened the crap out of those nuts - it's not impossible, but I don't think they would have come loose. Third was the test drive after the fact with silky smooth performance and lots of power. I'm not ruling anything out, and I may re-check my work tomorrow morning when the engine is cold, but for now I'm looking at other things.

Kerry, that sound like a good plan to me, so I checked all around the ALDA area to look for loose fittings, loose connections or anything of the sort. With my untrained eye, nothing was obviously different. Below are a couple of pictures that may or may not be helpful:

http://www.flickr.com/photos/51135442@N03/5946580479/

http://www.flickr.com/photos/51135442@N03/5947133868/

Where should I be looking for the line to the switchover valve?

Great that you added some pictures - they always help.

If you want them to show in the thread click on the picture of the sun and the mountains => little yellow box in the Reply box and add the link at the pop up prompt





EDIT - hey bugger that's not working - have you got some sort of security on these pictures?

__________________
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!

For the record... at over 30degrees C the MB book lists STRAIGHT 40 WT for these engines....

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

2.5 hours of highway driving is enough to 'un-do' any extreme adjustments to the valves. If you recall any of them being particularly tight, then this should be a high priority.


However, braking associated with 'stumbling' also raises concern with regards to the vacuum system.


-

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Tightening the crap out of things is not always good. There is a certain torque you put on things, too much can warp or strip.

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Cheers!
Scott McPhee

1987 300D

Follow that clear plastic line coming into the Alda over to the overboost protection solenoid and then around the back of the engine to the back of the intake manifold. I'm betting it's broken or disconnected somewhere.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Army - I posted them through flickr which doesn't allow direct linking

leathermang - yep, I use Delo 400 15W40 exclusively

jt20 - this is true; I only drove it for about 40 minutes total after the valve adjustment; would this be enough to dislodge something? The intake valves were sort of borderline, but I remember the exhaust valves being quite tight. Before the adjustment, the feeler gauge did not fit through several of the gaps.

Scott - you're quite right; maybe "tightened the crap out of it" was poor wording. It's hard to describe exactly how tight I made them, but they are together with about the same force as they were when I started. I am always conscious of the threads and making sure things are torqued properly.

It would be a strange event if something 'dislodged', especially considering you "tightened the crap out of them" ; )

...but the valve seats will wear just a little bit especially if they were tight. Most of this is due to deposits on the seats that are very soft in comparison to the valves. Once you get that thing going at highway speeds.... they beat the crap out of those deposits or any uneven wear and the valves get tight again.

-this effect would not be incredibly noticeable if all the exhaust valves were evenly tight before adjustment. Much more noticeable if one or two of them seemed really tight in comparison to the others.

-the fact that you mentioned about the stumbling corresponding to braking says something else.

Perhaps the stumbling occurred not because you pressed the brake pedal, but because you let off the 'go' pedal very quickly. Try this: Get back up to speed, then let off the 'go' pedal abruptly. If it stumbles, you may have air getting into the fuel.

If that is the case, replace the o-rings on the main fuel filter bolt.

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kerry - problem found! The clear lines look ok, but there's a set of wires that plug into the top of the manifold, just above the clear line. Those wires run (as far as I can tell) to the vacuum amplifier. It seems I'm guilty of another oversight; these wires are pinched slightly on the rear corner of the valve cover gasket. No oil leaking from that area, but the wires are definitely wedged in there.

jt20 - Thanks; I will give those valves a look over. And the stumbling is exactly what you described; it occurs when I lift off the gas pedal. I will go ahead and replace those o-rings.