My 2006 E320 TDI puts out an embarrassing amount of black smoke whenever I accelerate hard enough to cause a downshift. It is just a short (2-3 second) belch, but it is enough that I can see cars in my rear view mirror driving through the cloud. It just does not seem right for a car with 47K miles that has been taken care of very well.

Another important note: about 15K ago the dealer had to replace two glow plugs, the cylinder head (one of the glow plugs broke off as it was being changed), the turbocharger (it was making a bad noise), and the alternator. All under warranty, but now as the warranty is drawing near its end, I am worried that the smoke issue means I will be having problems again. Could it be related to my previous glow plug and turbocharger problems or is this normal? I am pretty sure I will be going back to the dealer, but I am interested in hearing the opinion of others as well.

That sounds incredibly not-normal for a cdi, they are supposed to make little to no visible smoke, ever. I'd think it might be a fuel injector issue....no idea, I've never even seen under the hood of one before.

Thats a scary amount of repairs and maintenance for only having 47k on it.....the whole head of the engine!

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-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)

I have no personal expirience with the CDI either, nor do many forum members as they are relatively new.

I'd have to agree that what you describe is not normal.

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)

I agree with others that it's not normal. You should not see any visible smoke during daytime, at most just a little bit in the headlights of the vehicle behind you at night when you step on it. How's your oil consumption? If none, I'd suspect the injectors. If it were my car I'd be using some injector cleaner + cetane booster. Red Line DFC or 85+ is a good one. I also like the DieselPower cetane booster. Both are available at PepBoys or Summit Racing. Usually I mix the 2 products using the minimum dosage suggestion. My cars have never been more smoke-free.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

Normally when a diesel smokes like that it is a timing issue. You may have the dealer check the timing of diesel injection. Good luck....

Any check engine light?

If I were you I'd get rid of the car while under warranty - what you're describing sounds highly abnormal - and an indication of really expensive repairs ahead.

I have an 83' 300D turbodiesel with more than 200,000 miles - and it puts out very little smoke under even full throttle.

Mine doesn't either and i have 287,000 some odd miles on it. Have this looked into right away! This should be something serviced by Mercedes Benz!

I have very limited experiance with an ML320CDI, that one didn't smoke that I could tell. I'd take it to the dealer and get them to fix it.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Does the CDI have a dipstick?

New heads? I wonder how much that costs?

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1985 500SL Euro w/ AMG bits 130k
1984 300SD Turbodiesel 192k
1980 240D Stick China 188k
2001 CLK55 AMG 101k
2007 S600 Biturbo 149k Overheated Project, IT'S ALIVE!!!

our CDI does that on occasion... its an 05 w/ 39xxx on it...

we've had leaky injectors replaced under warranty... cetane booster... && injector cleaner && a trip to the stealership for your car is in the near future...

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Matthew McIvor

2016 E350 4Matic Black/Black
2007 GL450 4Matic with Off-Road Pkg Silver/Black
1995 E300 Diesel White/Gray
1994 S600 Euro Black/ Black Velour
1986 560SL Blue/Blue/Gray
1986 190E Blue/Blue 93k

The comments have been very helpful, if a bit scary. Thanks to all. I'll make an appointment soonest and comment here how it turns out.

Such a wonderful car to drive, shame to have to be worried about the engine all the time. I am hoping there will be some big, obvious thing that completely takes care of the problem and I can go back to being more Zen while on the road.

No diesel, no matter how old, should smoke significantly if everything is working correctly. That's why I don't really get those articles that always talk about the old, "smoke-belching" diesels of the past. The authors of those articles are implying that it used to be normal for diesels to smoke in significant quantities, but that's not true.

No dipstick but I believe there's an oil level gauge on the dashboard somewhere or at least a low-oil idiot light.

That could be what the OP is experiencing. I didn't even think of that. This is a known occasional problem with common rail injection.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

I have an appointment with the dealer and will suggest the leaky injectors as the possible cause (not sure if there is a way to check for that).

Thanks again for the comments and ideas.

I beleive its perfectly normal. I used to drive 5 different cdi's as taxi's in Copenhagen. 3 320CDI's and 2 220CDI's. They would all act as you described. The 220's were worse because we pushed them harder. It would allways be a puff, never a continuous stream. They had between 80k and 300k on them.