W207 Fuel economy not as expected

[Mr_Mocata]

Hi all,

I recently bought a 2009 W207. It has 90,000 miles on the clock and is in excellent condition.
The only thing is I am only getting 30mpg. The research I did prior to purchase suggested the 3.5L V6 is surprisingly economical. This is not the case with my car however.
I have added so injector cleaner to the last tank of fuel. This seems to have had little effect.

My 2011 C220 Diesel gave at least 45mpg. I am expecting too much from the E350 or can anyone please recommend some remedial measures?
New injectors perhaps?

Any advice, gratefully received.

M

 

[LostKiwi]

Hi and welcome.
Your economy is highly dependent on your driving profile.
Short journeys and round town running kills economy on large engines.

 

[Mr_Mocata]

Hi and welcome.
Your economy is highly dependent on your driving profile.
Short journeys and round town running kills economy on large engines.

Thanks for your response Kiwi. The stats have been observed over long motorway journeys whilst driving very frugally. Consumption seems way high to me.

 

[Blobcat]

Hello and welcome,

What is your tyre pressure like and how wide are your tyres?

 

[JBell]

30mpg out of a 350CGi is bang on IMO

 

[Mr_Mocata]

Hello and welcome,

What is your tyre pressure like and how wide are your tyres?

Hi Blobcat and thank you!
The tyres are fairly wide, low profile jobbies. They are in good condition (two new rears) and have 33psi all round.

 

[Blobcat]

Hi Blobcat and thank you!
The tyres are fairly wide, low profile jobbies. They are in good condition (two new rears) and have 33psi all round.

Wide and lower pressures negatively effect fuel economy, quite a few are going back to 225 width with higher pressures

 

[Wighty]

Thanks for your response Kiwi. The stats have been observed over long motorway journeys whilst driving very frugally. Consumption seems way high to me.

What does the “book” say the car should be doing for consumption figures ?

 

[Mr_Mocata]

What does the “book” say the car should be doing for consumption figures ?

Hi Wighty!

The specs here suggest 47mpg combined. My mate who had one before me suggested this was about what he git from his.

https://www.ultimatespecs.com/car-s...lass-Coupe-(C207)-350-CDI-BlueEFFICIENCY.html

Cheers,

M

 

[LostKiwi]

47mpg is optimistic. The official figures are rarely if ever achievable in real life.

 

[Mr_Mocata]

47mpg is optimistic. The official figures are rarely if ever achievable in real life.

Agreed. 30mpg does seem really low though. Is there any general advice concerning developing / maintaining optimal fuel consumption beyond:

• Sensible driving
• Domestically available injector cleaners

Beyond the fact that the car is thirsty, I am really happy with it. It's ticked all the boxes after I lost my C220 CDi. A cracking vehicle in every respect.

 

[LostKiwi]

Yes I'd expect better than 30mpg on a motorway run - I can get better than that in my 2001 V6 petrol E class estate.

 

[CJD]

Correct me if I'm wrong, but isn't it a 3.0L ?
I know mine was, but it was a 14 plate, I could easily get 50mpg on a long motorway run with cruise set at 70.
Averaged about 44 over all, didn't have much town use though.

 

[malcolm E53 AMG]

Is it getting up to temperature ie is the thermostat stuck open it should get to 90 deg Centigrade quite quickly (3 miles) unless the weather is very cold. I changed the stat 2 years ago on my 12 plate E350cdi due to it sticking open and the fuel consumption was dreadful down to 20mpg. They tend to fail gradually (lazy) so I suspect yours is starting which will affect the mpg as the stat communicates with the engine management and is a factor in setting the fuel mixture.

 

[Wighty]

It does sound very low , I would have thought a gentle motorway run (with the consumption restarted) should be way above 30

 

[Dean Fletcher]

Hi Blobcat and thank you!
The tyres are fairly wide, low profile jobbies. They are in good condition (two new rears) and have 33psi all round.

Get them wackwd up to 37psi

 

[js190d]

Have a sniff of your engine bay. You may have some leaky fuel hoses. New air filter just cos it's easy.

 

[Srdl]

30mpg out of a 350CGi is bang on IMO

According to his profile, it’s diesel.

Correct me if I'm wrong, but isn't it a 3.0L ?

Yes, it is.

When I had my 2010 C207 350CDI (sold at 67,000 miles), I could expect between 43 and 46mpg on a motorway run. I actually saw 51mpg on a long run down the French Autoroutes one day.

 

[Mr_Mocata]

Correct me if I'm wrong, but isn't it a 3.0L ?
I know mine was, but it was a 14 plate, I could easily get 50mpg on a long motorway run with cruise set at 70.
Averaged about 44 over all, didn't have much town use though.

Now that's the kind of mileage I was led to believe I could achieve. Thank you. Now to find out why.

 

[Mr_Mocata]

Is it getting up to temperature ie is the thermostat stuck open it should get to 90 deg Centigrade quite quickly (3 miles) unless the weather is very cold. I changed the stat 2 years ago on my 12 plate E350cdi due to it sticking open and the fuel consumption was dreadful down to 20mpg. They tend to fail gradually (lazy) so I suspect yours is starting which will affect the mpg as the stat communicates with the engine management and is a factor in setting the fuel mixture.

Thanks Malcolm! That sounds promising. Is it a reasonably easy job to replace the thermostat or should I take it in?