1993 300D 2.5t weird smoke - PeachParts Mercedes-Benz Forum

cgunderm · #1 02-17-2007, 11:25 AM

Hi all,
I just bought a 1993 300D 2.5t, absolutely amazing car to me who only knew pre-1987s. 155K miles. Incredible acceleration. Smooth as silk. Tight steering, agile, yet like a tank at 80 mph on the highway. The weird thing about it is the following: it starts up super easy, even at 5 degrees after three days of not starting it, gp cycle runs once, starts up without any hesitation, you don't even have to touch the accelerator. It will then run totally smooth, no skipping, no smoking, for about 2 minutes. After 2 minutes, it will begin to run rough, not really rough, but skip every once in a while, and start blowing smoke. More than anything, the valves are quite clattery and loud, much louder than my 617s. Smoke not really heavy, but more than it should I think. It'll keep doing that until it's warm and I drive it, will belch a few clouds with the first accelerations, and then not smoke at all when driving, even under heavy acceleration. When you leave it idling for a while, it will start smoking again ever so faintly. Somebody suggested to me that it might have been overfilled with engine oil, and indeed it had. He said that with these models, the oil level has to be just under the max mark on the dip stick, and it was slightly above. I sucked out about 1 quart with the mightyvac to get it to be just under the max mark. And that improved the valve clatter somewhat, but hasn't stopped smoking yet (but I haven't driven it a whole lot since then). There are two other things that seem to be going on: There is a slight oil leak at the IP at the shut off valve. Additionally it just stopped shutting off with the ignition and you have to press the stop thingy. The vacuum line to the IP is not ripped off or anything. Do you think that this may have something to do with the smoke/valve clatter/skipping? Why does it stop the bad stuff when it's warm and it's an issue only when idling? Any ideas? Suggestions? There is no gunk in the water, so I don't think head/headgasket should be the problem. And because of the excellent cold starts and acceleration, I don't think compression should be the problem either.
Christian

benzforlife · #2 02-17-2007, 11:31 AM

what color is the smoke?

cgunderm · #3 02-17-2007, 11:54 AM

Hard to say at this ambient temp. because there is always some condensation going on as well, but I would say blueish/grey

babymog · #4 02-17-2007, 12:10 PM

When really cold, the 602 doesn't burn enough fuel to stay really warm, especially with the heater blasting and/or a not completely closed thermostat. Check the temp gauge. If the engine is running cold, it is possible that it will not burn the fuel completely and have a little white smoke. That will go away after the first launch, heats up the cylinders.

The clattering? Run some good oil, try something like Mobil Delvac 1 to clean it up, might be gummed-up lifters (hydraulic) from poor oil maintenance. Likely unrelated to the smoke.

Another possibility of the smoke (there are many possibilities) is the turbo leaking a little oil into the exhaust, when you accelerate the hot exhaust will burn the oil residue out of the pipes, then it is hot enough to combust without smoke until it idles again.

A couple of thoughts, good luck. Wunnerful engine and car.

sixto · #5 02-17-2007, 12:14 PM

Put the MityVac directly on the shut-off actuator on the IP to see if the problem is the actuator or vacuum getting to the actuator.

What oil are you using? If consumption is not an issue, try keeping the oil level between the upper and lower marks. [edit] I mean at the halfway point. Obvoiusly you'd keep it between the marks

I don't think oil level has anything to do with the smoke. Read up on fuel cleaners and additives. Lots of good things written about Lubromoly Diesel Purge.

Sixto
93 300SD 3.0

cgunderm · #6 02-17-2007, 12:16 PM

Thanks for the thoughts.... (more below)

Quote:

Originally Posted by babymog

When really cold, the 602 doesn't burn enough fuel to stay really warm, especially with the heater blasting and/or a not completely closed thermostat. Check the temp gauge. If the engine is running cold, it is possible that it will not burn the fuel completely and have a little white smoke. That will go away after the first launch, heats up the cylinders.

Nope, once up to temperature, the engine is running between 81 and 87 degrees. Has a new thermostat in there.

The clattering? Run some good oil, try something like Mobil Delvac 1 to clean it up, might be gummed-up lifters (hydraulic) from poor oil maintenance. Likely unrelated to the smoke.

According to previous owner, the engine has had Rotella T 5w40 synth for the last 2 years (but was driven only about 5K in those two years)

Another possibility of the smoke (there are many possibilities) is the turbo leaking a little oil into the exhaust, when you accelerate the hot exhaust will burn the oil residue out of the pipes, then it is hot enough to combust without smoke until it idles again.

A couple of thoughts, good luck. Wunnerful engine and car.

Yup, I'm blown away by how nice it is.

TMAllison · #7 02-17-2007, 12:26 PM

You've got a vacuum leak somewhere if it is not shutting down with the key. I would concentrate on that first.

I would leave the clattering/smoke alone for a while after fixing the above and see if having lowered the oil to the proper level and fixing the vacuum leak doesn't slowly improve things.

Is also quite possible you are hearing injector noise too rather than valves. I've been fooled twice by injector clatter sounding like valves. Diesel Purge (2 cans at a time) helps and is probably a good investment before jumping off into other more expensive fixes.

cgunderm · #8 02-17-2007, 12:27 PM

answers below:

Quote:

Originally Posted by sixto

Put the MityVac directly on the shut-off actuator on the IP to see if the problem is the actuator or vacuum getting to the actuator.

You mean, pull out the vacuum line that goes in there and stick the tube of the mightyvac in there instead?

What oil are you using? If consumption is not an issue, try keeping the oil level between the upper and lower marks. [edit] I mean at the halfway point. Obvoiusly you'd keep it between the marks

Literally just got the car (a week ago). According to the previous owner, the last oil change is about 4000 miles back and he hasn't added any oil since then (and I think he is honest, I trust him). It was still above max. so I think it's safe to assume that the consumption is not an issue.

I don't think oil level has anything to do with the smoke. Read up on fuel cleaners and additives. Lots of good things written about Lubromoly Diesel Purge.

This MB mechanic I talked to about it told me that when it's been overfilled (apparently easy to do with this model), the valves can't function properly and will get noisy, and there might also be smoke as a consequence. When I pumped out the quart a couple days ago, when I started it up afterward, there were splatters of black oil coming out of the tail pipe at first (not before the pumping off of the extra quart, though....) The valves are noticeably quieter now....

Sixto
93 300SD 3.0

babymog · #9 02-17-2007, 12:27 PM

BTW my 602 turbo runs just above the full mark when I change the oil, doesn't seem to affect anything.

barry123400 · #10 02-17-2007, 12:31 PM

Since it runs well for about two minutes initially. I suspect the car has a delayed glow plug extinguish. As soon as those plugs drop out the fuel is no longer burning well.
Thats the smoke you see until the engine warms a little. You could try to fine tune the car but it is really not harmful in my opinion. You could verify this senario by just monitoring the point at which the glow plugs loose their voltage and the smoke starts.
I would attempt to treat the lifters but it may turn out you require a new set. We used to use automatic transmission fluid in the oil but times have changed. Sometimes it helped sometimes not. Some report improvements with a total synthetic oil change as mentioned. Sometimes though they are just worn out.
Louder than a 617 is getting up there. . In general it does not sound like you have any serious problems.
Since you seem to be on good terms with the seller. He might know if the injectors were removed at 100k and checked. I think that is their recommended maintenance requirement.

cgunderm · #11 02-17-2007, 12:33 PM

more below

Quote:

Originally Posted by TMAllison

You've got a vacuum leak somewhere if it is not shutting down with the key. I would concentrate on that first.

Since it's not affecting other functions (transmission, heat etc.), is it safe to assume that it must be somewhere close to the shut-off valve?

I would leave the clattering/smoke alone for a while after fixing the above and see if having lowered the oil to the proper level and fixing the vacuum leak doesn't slowly improve things.

Does anyone think it might have to do with that little o-ring where it's leaking oil at the IP?

Is also quite possible you are hearing injector noise too rather than valves. I've been fooled twice by injector clatter sounding like valves. Diesel Purge (2 cans at a time) helps and is probably a good investment before jumping off into other more expensive fixes.

I'm pretty sure I hear the valves, since they get particularly loud when the car is warmer and the oil pressure goes down a bit, but get quiet immediately if you pull on the throttle and rev up. Injectors tend to make more racket when you rev up a little. Also, the previous owner says he just recently pulled the injectors and had them pop tested and they tested out fine. Might still be good to run Molly Purge, you are right.....

barry123400 · #12 02-17-2007, 12:42 PM

If the injectors where not checked until 150k then perhaps the timing has never been as well. Again talk to the previous owner. There would have to be some chain stretch over the years to modify the timing. Since this senario causes delayed injection it might contribute a little to the smoke.
I believe with the tool it is very easy to check the pump timing so it probably has been done. One cannot take anything for granted though.

sixto · #13 02-17-2007, 12:58 PM

Yes, apply vacuum directly to the little turret on the IP. You should see the stop lever move as you apply vacuum.

What o-ring is leaking on the IP? If it's leaking fuel at the base of the injector lines then, you need delivery valve seals. If it's leaking oil from the stop lever shaft or control rod sensor or some such attachment to the IP, that has no influence on fuel delivery or valve lash adjusters.

Sixto
93 300SD 3.0

sixto · #14 02-17-2007, 01:01 PM

Oh, leaking delivery valve seals, even if not leaking externally, can cause injector noise. You can loosen the injector lines one at a time with the engine idling to isolate injector noise.

Sixto
93 300SD 3.0

cgunderm · #15 02-17-2007, 02:26 PM

Nope, it's not the o-rings at the fuel delivery lines, it's on the side of the IP at the shut off valve, so we can eliminate that as contributing in any way to the smoke/valve clatter scenario.
I'll talk to the previous owner about the o-rings on the fuel delivery lines (on the IP), but I think he said he replaced them within the last 5000 miles.

Not sure about the timing of the pump and the chain. Will try to find out about that. I think he said he never looked at the chain.

Damn, I just popped the hood for the hundredth time since I got it, and now it won't shut properly any more. The little hook won't latch in. Happened to me with 2 other 124's that I looked at in the last 2 months. Is that what people were referring to in a previous post about the 124's not being as solid as 123's and 126's in the build quality?