W211 E270 fuel economy

[Cobra44]

I have had my 2003 E270 for 2 months now and reading some of the other past threads regarding fuel economy am slightly concerned.

I have done 3 brim to brim tests now and over 300+ miles with a combination of town and motorway driving at 70mph on cruise I'm struggling to get more that 34mph which seems low to me.

I love the car and it's only done 73k even though it's 10 years old. I should say I always have the air con on to avoid misting up but usually only on low 19c once the car is warmed up.

Any thoughts or suggestions. I don't expect it to do the 45mpg combined suggested in the manual, but 34mpg seems a bit low to me.

 

[Brianooo]

I am jealous my 1998 E300 td that does 26mpg and 30mpg on a run.

 

[mercmancdi]

My clk 270 cdi never under 37-40 short runs 50 ml trip at least 50 mpg
It was a 2005
now my cls is struggling to get over 33 mpg and the same 50 ml run in it is
37 mpg

 

[gizze]

Is it getting to temperature??

90ºc?

 

[Cobra44]

Is it getting to temperature??

90ºc?

I think so Gizze but I will check that today.

 

[Cobra44]

Is it getting to temperature??

90ºc?

Gizze, I have checked the temp this morning and it doesn't rise above 60°c on the gauge.

 

[mercmancdi]

Looks like (touch wood) you have found your problem ,
A cheap fix new thermostat makes it all the better .

 

[Cobra44]

Looks like (touch wood) you have found your problem ,
A cheap fix new thermostat makes it all the better .

Thanks Mercman....and that will improve the fuel economy?

 

[Cobra44]

Thanks Mercman....and that will improve the fuel economy?

I'm guessing the inference is it's running too rich because it's not reaching the correct operating temperature.

 

[mercmancdi]

Thanks Mercman....and that will improve the fuel economy?

It would make a good difference as your engine is not running at the correct temperture , I had a Peugeot 305 which was over heating and not worth fixing
So drilled 2 holes in thermostat so it warmed up a little for the heater as it was winter time , it dropped from 42 mpg to 30 mpg as the engine was running to cold . 60 is way too low for that engine . How soon does it reach 60% after starting

. If someone replaced the thermostat with the wrong one for the application (either colder or hotter), it can cause driveability, fuel economy, performance and emissions problems. So if the thermostat is replaced for any reason, it must be replaced with one that has the same (or correct) temperature rating for your vehicle.

 

[Ricardo_e220]

Can someone add a photo of the ideal temp gauge pic on a 211? Mine always hovers just above the 80 mark and I'm not sure if its right. Average mpg mostly motorway in 70k miles is 40...

 

[mercmancdi]

Don't have photo but my w211 sat at 87-88.

 

[mercmancdi]

I have photos of my 05 clk 270 cdi after 49 mls at ave 42 mph doing 57.6 mpg
On I pad I find it hard to load photos or I would post it .

 

[Richard Elliot]

You should easily get 40mpg, 45 with cruise on a long journey.
My thermostat needed replacing but tbh it didn't make that much difference to mpg. It is an easy cheap fix though, so do it anyway, and see if it helps. If you still can't beat 40mpg, then something else is wrong.

 

[gizze]

The car uses the temp to tell when it needs to overfuel, on BMWs from cold it over fuels by 40% depending on ambient air temperatures as well, and as it warms up the over fuelling is reduced until it gets to full temperature and then there is none.

My 220cdi used to sit at 60ish and was seeing mid thirties average on the obc, when the stat was changed (latest version that gets to 92ºc from Mercedes) it then jumped to mid 40's.

For the sake of making sure it is right just get the proper Merc one. I found Merc cheaper than anywhere else anyway.

 

[Ricardo_e220]

You should easily get 40mpg, 45 with cruise on a long journey.
My thermostat needed replacing but tbh it didn't make that much difference to mpg. It is an easy cheap fix though, so do it anyway, and see if it helps. If you still can't beat 40mpg, then something else is wrong.

Is this real mpg or obd mpg? Mine is 42.3mpg average on the obd and 40 real

 

[exjagman]

Can someone add a photo of the ideal temp gauge pic on a 211? Mine always hovers just above the 80 mark and I'm not sure if its right. Average mpg mostly motorway in 70k miles is 40...

Mine reaches full temp in about 3mls of town roads then sits at 90 degrees ish

 

[Ricardo_e220]

Mine reaches temp pretty quickly too. Ill take a pic of mine and post it tomorrow, not intending to hijack the op thread, but I have wondered as I read about 50 etc on here... I do mainly motorway and take it very steady so wondering if mine is as it should...or if its always been out....

 

[exjagman]

Mine reaches temp pretty quickly too. Ill take a pic of mine and post it tomorrow, not intending to hijack the op thread, but I have wondered as I read about 50 etc on here... I do mainly motorway and take it very steady so wondering if mine is as it should...or if its always been out....

I would have thought that it should be at normal temp driving normaly and only go up a bit if driving hard, From what I've read here I think 90 is normal.
I'm sure someone with more knowledge will tell you what it definately should be.

 

[Cobra44]

It would make a good difference as your engine is not running at the correct temperture , I had a Peugeot 305 which was over heating and not worth fixing
So drilled 2 holes in thermostat so it warmed up a little for the heater as it was winter time , it dropped from 42 mpg to 30 mpg as the engine was running to cold . 60 is way too low for that engine . How soon does it reach 60% after starting

. If someone replaced the thermostat with the wrong one for the application (either colder or hotter), it can cause driveability, fuel economy, performance and emissions problems. So if the thermostat is replaced for any reason, it must be replaced with one that has the same (or correct) temperature rating for your vehicle.

Hi Mercman. Just got back from a trip to Heathrow. Took 10 minutes from cold to reach 60°c and stayed there all the way up A303,M3 and M25. Struggled to 70-75°c in traffic jam going into Terminal 4. Looks like your theory is right.