W211 V6 Diesel

[mbenz1]

Hi all

Getting really annoyed now..

My father’s E280 CDI has been serviced a few weeks ago but still has a few problems, which I though would be eradicated after a service.

Average mpg is still at 22. After start, it stays around late 20’s (for a few minutes) but once on the main road (stop and go driving) it eventually decreases to early 20’s due to idling. If driving at constant speed, it increases but not fast enough to keep it at the late 20's mark, which is the correct mpg for this engine

Minor jolts can be felt just before braking to 0 mph – not all the time though. I assume thats to do with the gearbox?

Tapping / Diesel engine noises can be heard inside the cabin – quieter when engine is warm

We have done the following:
- Injector cleaners (around 3 bottles so far)
- Always used premium diesel fuel – first we used BP Ultimate but now use Shell v-power
- Local Merc approved specialist STAR diag. check – 02 sensor and glow plug relay replaced (brand-new genuine parts)
- Recent service using genuine MB parts and Mobil Oil
- ‘Italian’ tune-up – recommended previously on here

All these have made a noticeable difference but symptoms still exist – the car runs fine with fast acceleration and correct gear changes – no warning lights or messages and the engine/turbo has no odd sounds from outside. Suggestions and comments appreciated.

 

[mbenz1]

By the way, its a facelift version.

 

[mattc]

What temperature is your engine running at? Our I6 engined 211 is a few mpg down as a result (must fix now temperatures have warmed up-too nesh to fix whilst cold!)

 

[mbenz1]

mattc - It's runs at one bar above 80 degrees all the time (~85 degrees?) - I think that is the correct temp for the V6 engine.

 

[BillyW124]

Engine temp seems fine, Ours albeit 320 V6 runs bang on as you describe.

What also seems fine is sticking it on Star and reading the faults.

mine was suffering Low MPG and the fault was the lambda

Just recently we changed the glow plug relay as it was turning over at least 4 times before it started.

22 MPG on yours does sound low agreed.

From what you describe are you reading FROM START?

you mention stop and go driving, i'v learned to accept that this is a quick fire way to decrease the MPG on these cars.

On the weekend i clocked 350 odd miles return consisted of 98% motorway returning 32 MPG and I wasn't being frugal at all.

I'd do a test on a motorway run:

Reset your FROM START counter the second you enter motorway and see if your MPG decreases or maintains stable. Vary your speed also

You'll find MPG readings are hard to increase if you have been doing stop and go driving prior to getting onto the motorway.

By resetting it just before you enter the motorway it would give you a better scope.

The next time you do town driving pay attention to the MPG counter again resetting it and compare it to the motorway run

I also have the gearbox jolt you describe coming to a stop. New oil etc.

A slow stop from say 2nd to 1st gear. This only happens when gear box is cold. A software update hasn't cured it either. Yet to crack this one on the head! Once warm no jolting at all no matter how hard i try.

 

[sspeed]

I think the fuel consumtion you are getting is terrible..
I used to own a E320 Cdi (facelift 57 plate) and on my 10 mile run to work which is VERY heavily conjested I typically got 32 - 35mpg with an average speed of 10 mph (to give you an idea of just how conjested)..

On a motorway run (75mph) I typically got 45mpg and more than that if I tried..

See photo

 

[mbenz1]

Engine temp seems fine, Ours albeit 320 V6 runs bang on as you describe.

What also seems fine is sticking it on Star and reading the faults.

mine was suffering Low MPG and the fault was the lambda

Just recently we changed the glow plug relay as it was turning over at least 4 times before it started.

22 MPG on yours does sound low agreed.

From what you describe are you reading FROM START?

you mention stop and go driving, i'v learned to accept that this is a quick fire way to decrease the MPG on these cars.

On the weekend i clocked 350 odd miles return consisted of 98% motorway returning 32 MPG and I wasn't being frugal at all.

I'd do a test on a motorway run:

Reset your FROM START counter the second you enter motorway and see if your MPG decreases or maintains stable. Vary your speed also

You'll find MPG readings are hard to increase if you have been doing stop and go driving prior to getting onto the motorway.

By resetting it just before you enter the motorway it would give you a better scope.

The next time you do town driving pay attention to the MPG counter again resetting it and compare it to the motorway run

I also have the gearbox jolt you describe coming to a stop. New oil etc.

A slow stop from say 2nd to 1st gear. This only happens when gear box is cold. A software update hasn't cured it either. Yet to crack this one on the head! Once warm no jolting at all no matter how hard i try.

By START, I mean starting the car then driving. From the house to the main road, it takes a couple of minutes, and as the roads before the main road are empty, crusing at a constant speed is possible and in that time the mpg is in late 20's. Once on the main road, it's starts to fluctuate up and (mainly) down. As we don't travel on motorways much often, when we get a chance, will give the from start reset a go.

I am 100% sure the gearbox jolts come when engine is cold but will check if they come when the engine is warm.

I think the fuel consumtion you are getting is terrible..
I used to own a E320 Cdi (facelift 57 plate) and on my 10 mile run to work which is VERY heavily conjested I typically got 32 - 35mpg with an average speed of 10 mph (to give you an idea of just how conjested)..

On a motorway run (75mph) I typically got 45mpg and more than that if I tried..

See photo

Thats a good mpg return. In our case, when the car is used from the first start, the mpg is at 40 (after 4 hours of no driving it resets) and it comes down quickly to the late 20's mark, then from there it eventually reaches the early 20's mark (as mentioned previously).

I'm running out of ideas as to what the problem can be

 

[V12]

Have you done a tank to tank test?

 

[joecash]

I still believe the I6 3.2 litre diesel is one of the best Merc engines ever built for lastability and fuel consumption - just a shame the bolt ons (turbo in particular) aren't as good - coolant thermostats break down far to often too - gripe over

 

[mbenz1]

Have you done a tank to tank test?

What do you mean by a tank to tank test?

 

[jaymanek]

How are you measuring your MPG?

A tank to tank test is simple. You fill the car to the brim. You then reset your trip meter.
Then once you have used most of that tank with your normal driving, you then refill to the brim.

Take the litres the tank has taken. work out how many gallons... approx 4.5L to a gallon. Then take the miles you have done and divide by the gallons to get your MPG.

The only accurate way.

 

[joecash]

just another way of saying a brim to brim check. That is go to garage fill tank with fuel to brim - drive 2 or 3 hundred miles - go to garage fill with fuel to brim - check miles per gallon

 

[V12]

http://www.mpg-calculator.co.uk/

 

[mbenz1]

How are you measuring your MPG?

A tank to tank test is simple. You fill the car to the brim. You then reset your trip meter.
Then once you have used most of that tank with your normal driving, you then refill to the brim.

Take the litres the tank has taken. work out how many gallons... approx 4.5L to a gallon. Then take the miles you have done and divide by the gallons to get your MPG.

The only accurate way.

just another way of saying a brim to brim check. That is go to garage fill tank with fuel to brim - drive 2 or 3 hundred miles - go to garage fill with fuel to brim - check miles per gallon

Oh, I was thinking of something else... Yes, in the past, the tank was filled to full, and achieved under 425 miles from a full tank. This equates to a mpg reading of ~ 24, which means the trip comp is showing the correct fuel consm. Will do it again, since the car has been serviced recently.

 

[jaymanek]

425 miles from an E Class tank seems ok, need to know how many litres you used for that 425..

 

[BillyW124]

After dealing with the lambda on mines:

A week of driving to Oxford and back to London gave me this out of full brim approx 80litres of diesel.

mind you i was being fairly light footed as i wanted to clock 5 days @ 130 miles per day on one tank...

this was the result:




..cant be jacked now a days being frugal with the car as its so much enjoyable driving these things a bit spirited.

I must admit i love the w211 fantastic cars.

 

[BillyW124]

agree with the other chaps do a tank to tank test as well.

 

[mbenz1]

425 miles from an E Class tank seems ok, need to know how many litres you used for that 425..

I assumed it was a 80L tank. It is a okay return for an E-class but as it should be doing around 30+mpg in town, 425 miles from a full tank is less

After dealing with the lambda on mines:

A week of driving to Oxford and back to London gave me this out of full brim approx 80litres of diesel.

mind you i was being fairly light footed as i wanted to clock 5 days @ 130 miles per day on one tank...

this was the result:




..cant be jacked now a days being frugal with the car as its so much enjoyable driving these things a bit spirited.

I must admit i love the w211 fantastic cars.

Yep, our E280 CDI reaches roughly 40mpg on a motorway as well meaning it performs as it should on a motorway.


Out of interest, suppose this car was bought from a Mercedes dealership and was under the standard 1-Year Used Car Warranty. Assuming that the mechanics at the dealership tried all of the common methods to fix this mpg problem, but at the end they could not fix it, what would be the next plan of action by the dealership?

 

[mbenz1]

I have also noticed a quiet tapping sound from the engine, it sounds as if it is coming from the front left wheel side of the engine. It wasn't present before the service.... any ideas on what this could be. Thanks.

 

[DrNick]

Before you make any damning diagnosis, you've got to give it a fair go!

As a previous poster has said, give it a go up the motorway when its warmed up properly and reset the fuel meter just before you get on.

Drive at a steady speed for a few miles and see what you get.

Now reset it again, and try some hard acceleration Watch the reading plummet!

If you come to a hill try and coast down it (reseting the meter before you do). Watch how you can achieve stellar economy!

I suppose my point is that stop start traffic with a cold engine for short distance journeys will give bad mpg as consumption under these conditions is terrible. A longer journey with less stop start will get the average up. On mine it needs a 2 hour journey to give me what I would believe to be a representative figure of consumption at steady state. Remember the meter gives you an average, not an instantaneous figure. To get instantaneous you need to reset the meter so it starts again and so is averaging over fewer samples. And then keep resetting it.

If this still gives unacceptable figures, then there is a problem.
If it doesn't, then your typical journey profile is just not suited to getting maximum mpg from this car.

Sorry if I've missed the point and you've already done all this, but with big cars, and small journeys, small differences in conditions make a huge difference in my experience, so you just need to be happy that your test conditions are fair!