W211 E320cdi 7G poor consumption

[jon_viola]

Hi,

As you may have read I recently had to change the gearbox on my car. Ever since the mpg has been poor. Yesterday in mixed driving (m'way/country roads/city) I managed 30mpg. My old straight 6 E320cdi would have managed c40+mpg for the same run.

There are no fault codes showing on my reader.

Any suggestions?

 

[mbenz1]

My dad's E280 CDI V6 used to get a maximum of 25/26 mpg in town but the usual town mpg reading was around 22-23. The car was took care of with genuine service parts and premium diesel fuel (never used the normal diesel fuel) but still could not get above 26 mpg. Some V6 CDIs get really good miles to the gallon in town but we never experienced that.

 

[prprandall51]

Low tyre pressures? That makes a real difference to fuel consumption.

 

[V12]

What temp does it run at? Have you checked how accurate the obc is reading?

I6 will always trump V6 for mpg in the W211.

 

[Paddcomp]

My E320 returns 33-35mpg on a motorway run.

 

[E270 Owner]

You should make sure your tyre pressures are correct as already mentioned.

Those are low figures.

This is a mixed cycle of motorway and London traffic E320 CDI

Approx 48mpg on the motorway @ 70mph

 

[DSB SL AMG]

As a comparison what was the MPG pre trannie change?

 

[E280wilson]

My daily commute is 7 miles each way @ 60mph. The meter starts off at 42 and settles at 32-34. Never gets much better.

 

[jon_viola]

Thanks guys. The tyre pressures are at suggested rates.

The car has been serviced on the money by a specialist.

The car is new to me so not really got figures to compare as I only did c300 miles before the gearbox went.

 

[Gareth]

I'm confused as to whether you have changed gearbox or changed car. The I6 is well known for being much better mpg-wise than the V6. I tend to average low 30's in my V6 and at best 42mpg @ 70mph on the motorway over long distances.

 

[jon_viola]

Hi

Sorry not to be more clear. I had a I6 for two years then changed to a V6 hence the questions.

I didn't know they were known to be worse...

 

[V12]

If the car doesn't get up to running temp due to bad thermostat then it can decrease fuel efficiency by up to 20%

Last Monday I drove my S320cdi with I6 220 miles down to cornwall. It achieved 49.5mpg and was fully loaded with weight.

It was showing 52mpg for the first leg of the journey across hampshire and dorset but devon and cornwall and their many hills didn't help us out.

If you car runs at 90 degrees and your tyre pressures are up then try running a tank or two of injector cleaner through the system.
You should also do a brim to brim check to establish the accuracy of the OBC which is known to be pretty poor anyway.

 

[Rory]

Is there no way these days of "tuning" diesels like you used to be able to with petrol cars - tweak the ignition timing etc?

Surely the critical things would be the injector timing and quality of said injection?

 

[E270 Owner]

Get a remap done !!

 

[V12]

Get a remap done !!

Which will also make the obc even less accurate.

 

[jon_viola]

Remap already done.

Its been a city commuter car for the last 5 years i wonder if its a bit gummed up. I'll do some tanks of special diesel and see if it frees up...

Thanks for your suggestions- much appreciated!

 

[t-dawg1]

I get that quite regularly on mine! I use Millers Diesel additive at every fill

 

[ckember]

I was so disappointed with the mpg on e320 cdi v6 (2007) I complained to the dealers about it, they wouldn't admit the figures where poor

it used to get around 31mpg in mixed driving over a 50 mile run. In London traffic it could go down to 18-21 in the rush hour. Longer runs would be better, my current CLS GE does about 33-34 on the same route, so the brabus chip does improve things

 

[t-dawg1]

I was so disappointed with the mpg on e320 cdi v6 (2007) I complained to the dealers about it, they wouldn't admit the figures where poor it used to get around 31mpg in mixed driving over a 50 mile run. In London traffic it could go down to 18-21 in the rush hour. Longer runs would be better, my current CLS GE does about 33-34 on the same route, so the brabus chip does improve things

You should be getting up to 40mpg mate. I change my oil every 5k and use millers diesel additive hence I get over 40mpg quite regularly I

 

[t-dawg1]

Millers