The other night I noticed that under hard acceleration my 99 E300 was emitting a lot of white smoke that was plainly visible in the headlights of the cars behind me. But no smoke was visible in "normal" operation, i.e., w/o hard acceleration. Otherwise I have not noticed any problem, such as overheating, loss of coolant, oil consumption, loss of power etc. (The car overheated maybe 2 years ago when a hose broke) Revving the engine with the coolant reservoir cap off does not seem to disturb the fluid (I have seen a geyser effect many years ago in an Alfa Romeo of mine that did have a blown head gasket). In the daylight I cannot see any white smoke but my moron-level grasp of physics tells me that strong lighting from an angle makes junk in the air much easier to see. (colloquially known as the Tyndall effect) The engine might not have been fully warmed up when I spotted the issue, but I had been driving for maybe 15 minutes--actually cruising around checking diesel prices for a fillup! The car has around 135k miles, gets the recommended oil every 10k miles, and I am looking forward to at least another 100k! I haven't been doing a lot of driving in the last year or two but will take a long drive (160 miles each way--Philly to DC and back) this weekend and will try to see if the problem shows up when the engine is nicely hot after a long drive. But here's my question: Is white smoke under these circumstances a sign of a problem? (If so I'll take my wife's VW TDI instead) Or is there a more benign explanation?

 

After driving 15 minutes I would expect that your Engine would be up to operating temp. Have someone drive behind you during the Day and report on what type of smoke you have.

"The car has around 135k miles"; If it has that mileage on the original Injectors and they have never been at least checked I would say they are due for a rebuild.

Late Fuel Injection Timing will also cause you to smoke depending on how late it is.

The least expensive way to do that is to buy a Fuel Injection Pump Timing/Locking Pin that screws into a port on the side of the Governor Housing.
The specific Timing Specs should be on the Emissions sticker but in general it is set at 15 degrees After Top Dead Center; how much plus or minus degrees is allowed will be on the Sticker.
Or you can have a shop with the proper equipment do the Timing.

 

Thanks, all! Will have the bride follow me in the dark tonight.

 

I would do it during the day also. At night gary smoke is going to look like white smoke.

 

Update: Had the wife follow me with some hard acceleration and then we traded places and repeated the exercise. Bottom line: With me following her at the wheel of the E300TD I could not see much of anything. Just the occasional wisp of white smoke. Yet when I was at the wheel myself looking in the rear view mirror it seemed like a lot. I suspect there is nothing wrong after all. I may have been seeing an artifact of aerosol physics--the observation of a powerful light as it scatters through a cloud (i.e., an aerosol) varies greatly depending on the angle of view. And it can show stuff in the cloud that is invisible under ordinary light. Assuming the engine is operating properly diesel exhaust, like any other exhaust from an internal combustion engine, produces an aerosol cloud of particulates, vapor and stuff. That aerosol should be largely invisible in ordinary daylight as is the case with my car. But shining a strong light through the same aerosol in the dark may render the cloud visible, depending on the angle. It's not limited to exhaust. Think of the beam of a movie projector in a dark theater: depending on where you sit you may be able to see the shaft of light in the air. You see the beam because the powerful light is scattered by the vapors and particles in the air. And you may be able to see what look like individual particles floating in the air. That stuff is invisible otherwise.
I'll keep an eye on this--including in the daylight. Meanwhile based on the various comments I wonder if there is some specific interval for checking or rebuilding the injectors, fuel pump, etc. that I should be following. I have had all the maintenance on the car done by my local MB dealer since I bought the car in 2006 but I am growing distrustful. They seem to urge a lot of expensive work that my local garage insists is not needed, e.g., a recent recommendation to replace the brake pads and rotors ("Almost shot" vs. "no way").

 

Something I had been wondering about is that most Diesels under hard acceleration will put out some smoke. But, I am speaking of Vehicles with no sort of Computer in them.

On the Vehicles with no computer some light colored smoke under and during hard acceleration is normal and more so on an older Vehicle. But, should quickly clear up.

It could be that you put more Foot into the Pedal than your Wife does.

Concerning your local Mercedes Dealership you might do and internet search and see what others have to say about it.

The local one here in Long Beach, CA does not get good reviews from Customers concerning repairs from what I have read on the internet. Hope, I never have to go there for anything.

On issues concerning Diesels I am guessing there is several hundred Mercedes Gasoline Cars out there for every Mercedes Diesel. So, even the Dealership is likely better at working on the Gassers than the Diesels.
What is worse is that when you take a Car to a Shop they try to find more work on your Car for them to fix. As with the Brake issue you spoke of they can be inclined to try to scar folks into having work done.

 

>>What is worse is that when you take a Car to a Shop they try to find more work on your Car for them to fix. As with the Brake issue you spoke of they can be inclined to try to scar folks into having work done. <<

I'm told they work on commission!

 

It depends on where you work. The places I worked as a Diesel Mechanic I was paid by the Hour.
What I know from speaking from Guys that worked at a Dealership is the Mechanic gets paid a fixed amount of Money for a specific job no matter how long he takes on a job; a Flat Rate.
Each job has a different Flat Rate.

Under the Flat Rate the Company has decided that it takes X amount of time to do a job like replacing a Water Pump and only pays you for that amount of time
.
As an example if under the Flat Rate I was replacing a Transmission with a rebuilt one I would be looking for other work related to the Drive Shaft like replacing Flex Discs or the Driveshaft Support Mount/Bearing.
Why; because some of that stuff was already taken apart when I removed the Transmission making it easier for Me to beat the Flat Rate; meaning I can do the job in less time because some of the labor is already done when I removed the Transmission. More jobs done in less time equals more Money.

On some jobs it is easy to beat the Flat Rate like replacing Belts. A Mechanic who wants to do the job fast does not spend time removing the Belt; He cuts the belt an throws it away and spends the time installing the new Belt.

I am not sure in Private Shops. I have been told some Shops give the Mechanic a percentage of the parts they use. So Mechanics look for jobs they know they can beat the Flat Rate on and that has parts they can make Money on.

Then there is the other Guy or Gal; the Service Writer. That is the one who is likely to be working on Comission because that are most often Salse People and not Mechanics.

This is a Story I read in a Book on Auto Repair Fraud. A Lady came in and said She was hearing a noise from the Transmission. They replaced Her Transmission and afterwards the noise was still there.
The problem turned out to be that the Alternator had a bad Bearing and for some reason the Sound seemed to come from the Transmission.
So what happend in this story. The Service Writher saw $$s when the Lady mentioned Transmission and never told anyone to test drive the Car.
After the Transmission was replaced no one test drove the Car either (neither the Service Writer or the Mechanic gets paid when the Test Drive a Car).

On the other side the Service Writers Drinking buddies get more of the high paying jobs; the ones it is easy to beat the Flat Rate on then the less favored Mechanics.
The less favored Mechanics get stuck with the Warranty work the Bosses Drinking Buddies screwed up.
If you have ever done any Warranty work it is generally takes longer than the original job did.
And so on.

 

Here is a story from the Fuel Injection Shop I worked in.

Business had been slow.

Foster Farms bought in a Delivery Truck that had a 3309 CAT Engine in it.
The Engine had an obvious miss.

Normally We would have pulled and tested the Injectors (Stanadyne/Roosamaster Pencil Nozzle Injectors). But, My Boss was short on Money and told them the Fuel injection Pump needed to be rebuilt (we never checked the Injectors).

I rebuilt the Fuel Injection Pump and found nothing that could cause a miss. Put, the Pump back on the Engine and of course the miss was still there.

If the Fuel Injection Pump had been causing the miss it would not have seen much Fuel coming out of it.

My Boss told them it must be the Injectors so we pulled the Injectors to Test them.
While I was pulling the Injectors I bumped one of the Valve Springs and found that it was loose.

The Valve Springs were intact and My Boss was extremely happy because that meant we would be pulling off the Cylinder Head; more Money.

As it turned out a chunk of the Valve Face was gone and while it left a dent in the Piston head some how managed not to do any more damage.

So we also rebuilt or replaced the Injectors.

But, My Boss had misdirected them to begin with and cost them extra time and Money and we tied up their Truck for almost 1 month because some of the CAT Parts had to be ordered.

Here is what would have been the cheapest for the Customer. When the Truck came in we should have done an Injector Cut out Test.
Because on this Engine the Injectors are under the Valve Cover I would have loosened the Fuel Injction line at the Fuel Injection Pump cutting off the Fuel to the Injector.

On the Cylinder that had the miss cutting the Fuel off at that Injector would have not changed the Engine RPM.
Having identified the bad Cylinder we would have pulled the Injector and tested it. Even if it turned out the Injector was no good and we replaced the Injector and still had the miss at that point we would have supected something wrong in that Cylinder and investigated the issue futher.
Like a Compression Test or Leak Back Test.