E280 47.9mpg IMPOSSIBLE?

[Gipsyracer]

My first post, so please excuse any obvious errors!



I'd like to start by thanking the community here for a really useful forum. I collected my 2007 E280 Avantgarde Estate S211 7-speed auto from its first owner last week and I'm really delighted with my purchase. Even more delighted that someone else paid 30-odd grand more than I did for what is pretty much a new car. I've already found answers here for everything from cup holders to towbars.

Much is written here and on other forums on the subject of fuel economy but I can't find the answer to my seemingly simple question: The published extra-urban mpg is 47.9. This "fact" is blindly repeated in pretty much every road test or review I have found. Has anyone ever seen anything close to 47.9mpg other than by towing the car or dropping it off a cliff? What exactly are the conditions which must be replicated to achieve the M-B claimed economy? I'd love to know the answer, because it could save me about £1000 per year in diesel.

My weekly commute is 242 miles each way from Manchester to Maidstone, all A-road or motorway. I've driven it twice now like an old man, hardly touching the brakes and trundling along just below 70mph. No heavy acceleration. I get an indicated 40.2 mpg for the journey, which is 16% worse than what is supposedly possible. By comparison, my old 1.9TDI passat (claimed extra-urban 57mpg) gave an indicated 57.9 on the same trip, driven the same way (and coasting down the hills, which admittedly is not possible with an auto).

First let's rule out the obvious. 92k miles so just run in, full service history, fastidiously maintained, everything appears to be working right, no black smoke or gearbox over-revving. Running at about 90c, warms up quickly and stays steady. Tyres pumped up to 34psi. Nothing in the boot. No roof rack. I've given it a bit of a thrashing to clear out the cobwebs. Not yet double-checked by brimming the tank.

[FONT=&quot]What do you reckon?[/FONT]

 

[BlackC55]

Do you use quality diesel?

Give it an "Italian tune up" with some fuel system cleaner and see what its like after.

Are the tyres a good make?

 

[BTB 500]

The published extra-urban mpg is 47.9.
...
I've driven it twice now like an old man, hardly touching the brakes and trundling along just below 70mph.

Did you know that the average speed for the extra-urban fuel consumption test is 39 mph?

 

[renault12ts]

I've just driven 31 miles...the indicated mpg is 46. I have achieved more than 50 (real not indicated).

 

[Gipsyracer]

Chaps,

Thanks for your input.

Tyres are top quality (can't recall the exact brand), medium worn so the rolling radius should be about right in the trip computer calculation.

I use supermarket diesel, either JS or Tesco.

I'll give the fuel treatment a whirl. How is it supposed to work and what are the actual benefits? Anyone recommend a brand?

By the way, I am a mechanical engineer by profession and hence a bit skeptical by nature of fuel treatments, magic beans, pellets etc. which purport to improve economy!

 

[Gipsyracer]

Did you know that the average speed for the extra-urban fuel consumption test is 39 mph?

Crikey! It would take a very long time to get home at that rate. Still, aerodynamics only start to make a big difference above 55 so I am still a long way off what should be possible.

 

[BlackC55]

The fuel treatments do work. Millers is a good brand. Cheap tyres have a greater rolling resistance.

 

[Gipsyracer]

Right, then. I'll pour in some snake oil, give it a good thrashing over the snake pass on the way home tomorrow, drive back down South like an old duffer on Monday morning and will report back with the results.

 

[MancMike]

Injector cleaners do work. They're not snake oil.

The spray pattern is very important from an injector and a partially blocked injector will squirt like a kids squirt gun, which is terrible for efficiency. Cleaners help dissolve the blockage and restore the spray pattern to an atomiser style mist.

My C280 3L Petrol V6 on paper says 40 mpg extra urban and I've been able to get 35 mpg with 4 people in the car on a long run at 60 mph.

My old little run-around would report that 60 mph is 10 mpg better than 70 mph. (60 mpg up to 70 mpg) Although that was a very efficient little car so it won't make nearly as much of a difference to a thirstier, bigger car.

 

[ShinyF1]

I've just driven 31 miles...the indicated mpg is 46. I have achieved more than 50 (real not indicated).

How do you do it? The best I have mustered from my old hearse is 37mpg

 

[Deleted member 37751]

On a good run, I achieved 50mpg quite regular in my W211 E320 V6 CDi Sport:

 

[renault12ts]

How do you do it? The best I have mustered from my old hearse is 37mpg

Driving from Wales to London...slowly due to traffic.

 

[BlackC55]

I think the 320 is better on fuel than the 280. More torque is the key.

Have you considered a re-map to improve economy?

 

[renault12ts]

Edit

 

[merc85]

Brim then drive X distance brim again then work it out properly, i easily get 50mpg and at best 61mpg out of my 320cdi

 

[markjay]

As BlackC55 and i-CONICA said, fuel additives are essentially detergents and clean the fuel system and valves. They do work.

If you can't be bothered with additives, then opt for Premium fuels instead - BP Ultimate or Shell V-Power - they contain the required additives in the correct ratios. A few tankful of Premium fuels will do the job.

There is also a product called cataclean, though the manufacturers claims are controversial. See http://www.cataclean.com.

 

[V12]

OBC is not accurate. Did you brim to brim check your Passat to find what margin of error you had?

I find most MB to be around 10% optimistic but I have seen some the other way. We have an E240 estate which recently displayed 22mpg on a trip to london but once measured it actually returned 32mpg.

 

[mbenz1]

To the original poster, if possible and circumstances allow, then always use premium diesel fuel (Shell V-Power or BP Ultimate) since they will most likely give better fuel economy than the cheaper stuff you get in supermarkets and will definitely take much greater care of your engine and promote its longevity.

 

[RKC-benz]

Injector cleaners do work. They're not snake oil. The spray pattern is very important from an injector and a partially blocked injector will squirt like a kids squirt gun, which is terrible for efficiency. Cleaners help dissolve the blockage and restore the spray pattern to an atomiser style mist. My C280 3L Petrol V6 on paper says 40 mpg extra urban and I've been able to get 35 mpg with 4 people in the car on a long run at 60 mph. My old little run-around would report that 60 mph is 10 mpg better than 70 mph. (60 mpg up to 70 mpg) Although that was a very efficient little car so it won't make nearly as much of a difference to a thirstier, bigger car.

Do you think I should try cleaning additives in my 1995 E280 S124? It swallows petrol like it's closing time!

If so, which ones, why, and what will I expect to happen?

 

[RKC-benz]

^^ mine is petrol by the way with 95k miles