REALLY low mpg!

[October]

Hi Folks,
I recently bought a 271 engine, 2004 C180k, petrol auto.
I recently brought it back to the dealer to get the O2 sensor replaced after the engine light came on.
Since I've had it back, I've been averaging 17.5mpg - mostly suburban driving, 30/40 mile an hour zones.

Could you please help me get to the bottom of this?
Could any other 2004/2005 petrol C180k owners out there let me know what they are averaging in mpg?
At this rate, I'm not even getting 200 miles from a tank.

Help!

Steve.

 

[neilz]

Well, my W124 E220 coupe did 28mpg, so a more modern car with a smaller engine should be doing much more. To put it into perspective, my current W140 S320 LWB (about twice the weight of the W124 and a lot more powerful) does up to 17mpg at best (ignore the Fuelly in my sig, I'm yet to correct the values and add new ones).

I think your car should be getting much more mpg

 

[fatdazza]

Hi Folks,
I recently bought a 271 engine, 2004 C180k, petrol auto.
I recently brought it back to the dealer to get the O2 sensor replaced after the engine light came on.
Since I've had it back, I've been averaging 17.5mpg - mostly suburban driving, 30/40 mile an hour zones.

Could you please help me get to the bottom of this?
Could any other 2004/2005 petrol C180k owners out there let me know what they are averaging in mpg?
At this rate, I'm not even getting 200 miles from a tank.

Help!

Steve.

Around town I tend to get 25 mpg
Steady 70 around 38mpg

Drive like a saint on a long run at 60 ish I get 44mpg

 

[wemorgan]

Quite a few factors to consider. But as a benchmark to your specific car's potential, drive up and down the motorway at 60mph for 100 miles and measure the economy then. If the economy is still lower than anticipated then there's an issue with your car that needs resolving, which I'm sure the forum can help you with again.

The test is boring I know, but it eliminates the speculation which often follows these types of threads.

 

[Stratman]

Remove the spark plugs and see what colour they are. They should be a light tan colour. If they're black and sooty you have an over rich mixture. If they're the correct colour I'd start looking for a leak.

Or ease up on the 0-60 tests

 

[stevieb15]

Well, my W124 E220 coupe did 28mpg, so a more modern car with a smaller engine should be doing much more. To put it into perspective, my current W140 S320 LWB (about twice the weight of the W124 and a lot more powerful) does up to 17mpg at best (ignore the Fuelly in my sig, I'm yet to correct the values and add new ones).

I think your car should be getting much more mpg

When you say "at best" is that a mix of conditions?
The worst I've seen from my W126 500 is similar to your best and on my weekend run to Sussex and back I'm looking at 25 plus.

 

[clk208]

My car now gets around an additional 5mpg after replacement of a duff lambda sensor, spotted at MOT time as emissions were a little high.

I didn't realise there was an issue as MPG was within what I would expect to be normal limits and performance was fine.

The new sensor probably paid for itself in fuel saving over a few months. Might be worth a hookup to STAR to get your car checked out.

 

[October]

But as a benchmark to your specific car's potential, drive up and down the motorway at 60mph for 100 miles and measure the economy then. If the economy is still lower than anticipated then there's an issue with your car that needs resolving, which I'm sure the forum can help you with again.

That would cost me £40 at this rate!

 

[wemorgan]

That would cost me £40 at this rate!

plus my fee!

 

[October]

My car now gets around an additional 5mpg after replacement of a duff lambda sensor, spotted at MOT time as emissions were a little high.

I was hoping that that was going to be the same for me! Alas, not. If anything, it's made things worse.

I'll check the spark plugs over the weekend.

 

[October]

Also, when I switch the engine on, it, erm, coughs(?) for a few seconds before settling down and sounding normal. Any ideas what that might be related to?

 

[Henry D]

Is the temperature gauge getting up to midway when hot?,as a cool running engine will consume more fuel.

 

[neilz]

When you say "at best" is that a mix of conditions?
The worst I've seen from my W126 500 is similar to your best and on my weekend run to Sussex and back I'm looking at 25 plus.

"At best" is 70mph motorway driving. In London it does ~12mpg

 

[malluboy77]

Fatdazza's figures look very familiar to what I see often. My numbers fall to early 20's if traffic is heavy. Worst figure I have seen is 14.6 and best is 45 mpg, but rarely see these numbers. Perhaps worth plugging into a STAR machine..

 

[ray_hennig]

Wow!!

To put it into perspective, my current W140 S320 LWB (about twice the weight of the W124 and a lot more powerful) does up to 17mpg at best

I'm not surprised it only does 17mpg. Twice the weight of a W124? Is it bomb-proof?

RayH

 

[neilz]

I'm not surprised it only does 17mpg. Twice the weight of a W124? Is it bomb-proof?

RayH

Well, funnily enough, when I took it to Mercedes to have a couple of small issues fixed when I first got the car the man there said "you do know it's bullet proof don't you?" I didnt, but I do now!

 

[steve333]

Hi Folks,
I recently bought a 271 engine, 2004 C180k, petrol auto.
I recently brought it back to the dealer to get the O2 sensor replaced after the engine light came on.
Since I've had it back, I've been averaging 17.5mpg - mostly suburban driving, 30/40 mile an hour zones.

Could you please help me get to the bottom of this?
Could any other 2004/2005 petrol C180k owners out there let me know what they are averaging in mpg?
At this rate, I'm not even getting 200 miles from a tank.

Help!

Steve.

Hi i use to have a 2005 c180 & averaged around 30mpg in 3 years of ownership & would suspect something is definately wrong,as has been mentioned get the car to a good independant garage with star & get the codes read to see what shows up.

 

[grober]

Was it an MB dealer that replaced the lambda sensor? Does your car have 2 lambdas ? pre AND post catalytic converter? I wonder if you have a partially collapsed cat? As recommended above get the codes read by someone who knows what they are doing.

PS THIS THREAD MIGHT ALSO GIVE YOU SOME IDEAS? http://www.mbclub.co.uk/forums/engine/99266-odbii-p0171-possible-maf-problem.html

 

[ray_hennig]

Blimey!

Well, funnily enough, when I took it to Mercedes to have a couple of small issues fixed when I first got the car the man there said "you do know it's bullet proof don't you?" I didnt, but I do now!

Well, I stand corrected.

RayH

 

[Deleted member 6183]

It should be miles better than that, my old 180 C class did 43mpg when booting it (with no regard for economy) through France one year.