My fuel economy

[MancMike]

After reading the thread about all the C63s getting comparable figures to me, I'm a bit concerned...

My M272 E30 (3L V6 Petrol) has just clocked onto 88,000. It has a FMBSH until about 40,000 and the same indi FSH until 82,000 when I bought it.

I changed the oil, oil filter, plugs, air filters at 85,000.

I've averaged an indicated 16mpg over 3,000 miles (that's just when the trip was last reset).

My commute is 4 miles. With 0.5 miles 30mph, 1 mile of 50mph, then 2 miles of 30mph.

If I get a good run to work with little traffic, good luck with the lights (so, stopped at only one or two of the 6 sets I go through on the journey, keeping light on the gas, so it upshifts below 2k rpm, anticipating lights to come off the gas and be free-rolling as much as possible, basically a huge effort to use as little engine as possible, I can only make an indicated 21mpg. If I sod it and put my foot down, I'll get to work with about 17mpg indicated.

On the motorway, I'm not so bothered, as I reach 30mpg fairly easily, 35 if really careful (56mph left lane, cruise), and I've once managed 39mpg indicated.

Do others with the same engine have the same economy? I'm not concerned about the money, I'm worried about the engine. Also, I thought the mpg readout was programmed in/calculated based on what it thinks it'll be using in a given gear, given RPM, rather than measured what the injectors are actually squirting, so it seems this terrible economy is programmed in then, and my real consumption is even less if I do tank to tank calculation.

It's disappointing that those with 3.2L and 2 cylinders more than me get comparable economy figures as I've got about half the power (231bhp/300nm).

Thanks for reading. Thoughts very much welcomed..

 

[renault12ts]

Just to rule it out...but have you done a brim to brim test.

My commute is 5 miles, all at 30-40 stop start...and yes I know I have a big diesel...but I get 22mpg. This is half of what I'd get on a long run...and tallies with you getting half of what you'd get on a long run.

My wife's commute is about 3 miles...she gets 18mpg in her RAV4 petrol!!

 

[MancMike]

I have, and the brim to brim figures are 2 or 3mpg less, than indicated. I've not calculated exactly what % so it can scale, as I only did brim to brim calculation once as I tend to keep the fuel tank light.

I've got brand new Goodyear EfficientGrip Performance on the rear, which are very good on fuel

Tyre pressures all maintained at 32psi rear, 29 front.

I'm not so concerned about the overall figure over 3,000 miles as that includes a lot of "sod it" miles where I've put premium fuel in and gone for a blast, that gets the average over the journey into the low teens.

It's when I'm driving like mrs daisy, sticking to the limits, pulling away very gently keeping it below 2k, I can't seem to get any better than 20mpg, which seems comparable with the huge C63 engine figures.

 

[MBDevotee]

But your commute is over as soon as the car is warm. No car, petrol, diesel or even LPG is going to give decent economy.

You are the target market for a plug in Hybrid or even totally electric car.

How about an old smart car (£30 road tax) to commute and keep the nice car for other drives?

 

[MancMike]

But your commute is over as soon as the car is warm. No car, petrol, diesel or even LPG is going to give decent economy.

You are the target market for a plug in Hybrid or even totally electric car.

How about an old smart car (£30 road tax) to commute and keep the nice car for other drives?

Hi, Thanks. It's a good point that the engine isn't fully up to temp when I'm done, as I know engines use way more fuel when warming up... Maybe that's part of it, but still, others with similar or bigger engines seem to average better with similar commutes.

As said, not so worried about the cost so long as I'm getting what I'm supposed to be getting.

I'm not interested in electric cars other than the SLS electric and the Tesla, but those are very much out of my reach.

 

[R2D2]

Hi my M272 C350 showed an overall mpg of 27mpg my current M276 is currently showing 29.1 mpg. I seldom have seen either car in the teens but frequently in the twenties. A proper run will see 35mpg plus which I'm more than happy with.

 

[Bellow]

My commute is 4 miles. With 0.5 miles 30mph, 1 mile of 50mph, then 2 miles of 30mph.

The only meaningful C63 comparison is with one also doing the above. I suspect you would sleep easier if the result of that was forthcoming.

 

[MancMike]

Hi my M272 C350 showed an overall mpg of 27mpg my current M276 is currently showing 29.1 mpg. I seldom have seen either car in the teens but frequently in the twenties. A proper run will see 35mpg plus which I'm more than happy with.

Hi, Yours is the bigger 3.5L M272 E35 isn't it? I think that has common rail fuel injection which gives it better economy despite being bigger.

 

[R2D2]

Hi, Yours is the bigger 3.5L M272 E35 isn't it? I think that has common rail fuel injection which gives it better economy despite being bigger.

My last car was the M272 3.5 and I believe that was the same as your but bigger. My current C350 is a M276 Blue Efficiency cgi etc. and uses a bit less fuel in part due to the stop start technology.

 

[Bellow]

To throw some numbers into the mix.
I just calculated the last-tank mpg of my (petrol) car which will normally give me low 50s mpg on a run. This last-tank was 44mpg - and while 80% of it was long run, 20% was short run (working on the brakes and subsequent testing, short trips to the village for parts, etc, - but still driven quite gently) there is 25% extra mileage to be had in exclusively long running.
Now apply that extra 25% to your gentle commute figure of 21mpg and you are 26-27mpg - not so far from your easy 30mpg long run figure.
Factor in the remaining differences in this comparison - namely, my short running was a mere 20% of the tank-full, and that my engine is a mere 700cc(!) and your 16-17mpg in all probability is a consequence of your commuting regime.

 

[MancMike]

Thanks, all starts to sound reassuring then.

700cc

Your engine is 700cc?

Is it a smart car? I bet that warms up quickly.

 

[Ted]

Get the engine warm, reset the trip computer and go for a decent run.
That should give you a better idea, and should give you almost double.

 

[MancMike]

Get the engine warm, reset the trip computer and go for a decent run.
That should give you a better idea, and should give you almost double.

I've done this, that's how I managed 39 mpg once.

I'd gone to scotland to buy something, and so once there I reset the computer and drove back. Was at around midnight, no traffic, smooth all the way.

I'd already done experiments repeatedly resetting it on the way there to see over a few mile average, exactly what speed is best for economy, and about 56~58 seems to be the pinnacle. So used that on the way back and managed 39. I'm fairly sure It's not possible to get any higher than that with the effort that took...

 

[Bellow]

Your engine is 700cc?

Yep. 700cc with a turbo. It only has to punt 730kg up the road though.

Is it a smart car?

Yep.

I bet that warms up quickly.

Yep - that's where large engines really hurt economy. In their slowness to warm. They are just a large kettle at that point! Unavoidable physics.

Thanks, all starts to sound reassuring then.

It would be more reassuring if the C63 brigade would confess their short trip mpg - as if!

 

[MancMike]

Yeah I mean if someone with a C63 wants to swap C Classes for a week and enjoy better fuel economy while I get single figures, that seems like a worthwhile experiment to me.

(I mean if you can cope with only 3L and a mere 6 cylinders that is. )

 

[Bellow]

Some (slight) consolation for you.
While I was getting the smart MOT'd yesterday I asked about the mpg the trucks the garage owner and his son have recently acquired. Both of them are mid 1960's Ford F-Series pick ups, one with a 3.6 straight six, the other has a 5.0 V8. Merely starting up the 3.6 truck and moving it from the garage to outside causes the fuel gauge to move position. Ouch!

 

[st13phil]

My commute is 4 miles. With 0.5 miles 30mph, 1 mile of 50mph, then 2 miles of 30mph.

This is the root cause of your apparently poor fuel economy. The engine is never hot, so is very inefficient.

The biggest risk to the engine with this sort of driving regime is internal corrosion caused by the oil never getting hot enough for the condensation caused by combustion to evaporate off - you really should change the oil more often with a usage pattern like that.

 

[Bellow]

Add to the above fuel washing oil off the cylinder bore and dilution of the oil with fuel.

 

[MancMike]

This is the root cause of your apparently poor fuel economy. The engine is never hot, so is very inefficient.

The biggest risk to the engine with this sort of driving regime is internal corrosion caused by the oil never getting hot enough for the condensation caused by combustion to evaporate off - you really should change the oil more often with a usage pattern like that.

Thanks Phil. I think you're right... But I can't fathom those that never lift the bonnet. I change the oil regularly. It does get the odd longer run, but my commute is brief. I know any engine running cold is brutal for it. So I'm gentle until it's warm. I never take it into higher revs until it's fully up to temp.

I'm starting to understand it's very much down to my driving style and commute which is giving me such terrible consumption. I think my engine is perfectly healthy. It's certainly well looked after...

I'd still like to see some C63 owners post some figures if they have similar commutes...

 

[the prince]

My CLK 230k A208 is showing around 26mpg on my commute to work. I've got 2 miles urban driving to motorway, 18 miles on motorway then 3 miles through urban again. So basically a 23 mile journey taking on average 35 minutes.

Watching the speedo whilst driving i see that from standing the car is running at about 14pmg but this picks up as soon as it hits a steady constant 65mph and it creeps up ever so slowly to around 26-27 average mpg, after 30 minutes of driving.

I guess an average of 15mpg urban -25mpg motorway is about what to expect when driven conservatively.

Anyone else have a CLK 230k and know what theirs averages on a run?

This is somewhat different from my Peugoet 205 which has returned an average 55+mpg over the last 40,000.

Glad i've only got the CLK as a summer car with 5k limited mileage.