C200 and MPG

Seanalf

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Llanhilleth
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C200 CDI Sport 4dr
Afternoon all. So I've had the car for a month now and I'm looking for a little advice on MPG. I drove to see @Gazwould the other day and he commented that my MPG seemed a little low. I'd driven 68miles with a mix of good A road, motorway and a little driving through Bath. I arrived with the car showing about 46mpg. The car has only done 40k, so a lack of driving could be the answer, but I've done a chunk since so hoping it would have blown the cobwebs out a bit sooner lol.

Set up as follows:

A/C on auto at 20 degrees
Mostly in E mode (occasionally Manual mode)
Not a heavy right foot
Pressures all at 36psi (AMG 18" staggered), tyres with loads of life
Re-map to 200bhp, but no fault codes showing at the time of mapping and the economy is the same since
Without physically checking, a new air filter and oil change done 2k ago when I bought her
Stuck to speed limits

Did a long run to Bournemouth a few weeks ago (200 miles), put a bottle of redex in for the journey, got around 51mpg, I engage cruise pretty much as soon as I get on the M4, best I've had was 53mpg showing after a reset and getting on the M4 pretty much straight away (but in the 60mph limit for a good portion of the journey).

The car seems to be running fine, no lumpy idle, comes up to temp ok and doesn't drop when stationary. I'm not disappointed, I was getting about the same from my 75 manual, was just thinking I might get a few more, or this this about normal except for the motorway runs?

So the question is, where should I start looking? I was thinking maybe MAF (clean or replace), another bottle of Redex, thermostat (if it would make any difference), putting the car in for a service at an indie in Cardiff and see if anything comes up on a health check? Any other suggestions or confirmations I'm worrying over nothing?

Thanks all.
 
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Seanalf

Seanalf

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C200 CDI Sport 4dr
I would see what you can get with cruise control off, it's terrible for economy.

That's option one, but I do tend to have to drive a few hundred miles in one go and it helps with fatigue (I'm 53 and have knackered knees lol). On a motorway is it much worse as it reduces throttle creep?
 

W1ghty

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Might be the map reducing mpg ?
Unless the thermostat is not showing around 90 degrees then it’s not that causing it .
 
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Seanalf

Seanalf

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Might be the map reducing mpg ?
Unless the thermostat is not showing around 90 degrees then it’s not that causing it .

The mpg hasn't changed since the map to be fair, plus I don't drive hard at all, I'm quite light footed. I've only used the extra grunt a few times in the back roads for overtaking, I don't power onto slip roads etc.

I've just been out to the car, the MAF looks original, it's the Continental one
 

Fununcle

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That's option one, but I do tend to have to drive a few hundred miles in one go and it helps with fatigue (I'm 53 and have knackered knees lol). On a motorway is it much worse as it reduces throttle creep?
I completely agree that cruise control takes a lot of the strain out of long drives but it will have a detrimental effect on mpg. Pays your money takes your choice.
 
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Seanalf

Seanalf

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I completely agree that cruise control takes a lot of the strain out of long drives but it will have a detrimental effect on mpg. Pays your money takes your choice.

I shall give it a go on the next run
 

markjay

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My experience is that CC tends to speed-up rather harshly and then use the brakes to slow down the car - it can't plan ahead well enough in the same way a human drive does.

As for tyre pressure, isn't 36psi at the lower end of the scale? I would try 38 at the front and 44 at the rear (cold tyres).

Also, 18" tyres will never provide great fuel economy... they are far too wide for that. But that's academic, since you are unlikely to drop the wheel size to 16".

And, a tankful of V-Power, or a bottle of Diesel fuel additive, might help clean the injectors a bit.
 
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Seanalf

Seanalf

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My experience is that CC tends to speed-up rather harshly and then use the brakes to slow down the car - it can't plan ahead well enough in the same way a human drive does.

As for tyre pressure, isn't 36psi at the lower end of the scale? I would try 38 at the front and 44 at the rear (cold tyres).

Also, 18" tyres will never provide great fuel economy... they are far too wide for that. But that's academic, since you are unlikely to drop the wheel size to 16".

And, a tankful of V-Power, or a bottle of Diesel fuel additive, might help clean the injectors a bit.
I shall put some more air in the tyres tomorrow then fella, I put some Redex additive in a about 600 miles ago, so I'll get some more

What about the MAF? Is there any way of testing it or getting a readout to see if it's in tolerance?
 

markjay

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I shall put some more air in the tyres tomorrow then fella, I put some Redex additive in a about 600 miles ago, so I'll get some more

What about the MAF? Is there any way of testing it or getting a readout to see if it's in tolerance?

I don't know, have a search on Google and YouTube, but if I was in your position I would invest in an iCarsoft MB diagnostic scanner (or Carly) and check for any fault codes, then look at live engine data.

@KillerHERTZ can provide a discount.
 

SpiceWeasel

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I just recently got a 2013 C200 (auto) and I was expecting more mpg tbh. A 30 mile run with mostly single/dual carriageway showed 45mpg. Mine is only 136bhp but on 18" wheels. I am hoping after a good service things might improve a bit. I have the AC on auto set to 20c as well. My temp gauge looks to be around 85-90c ish
 
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Seanalf

Seanalf

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I just recently got a 2013 C200 (auto) and I was expecting more mpg tbh. A 30 mile run with mostly single/dual carriageway showed 45mpg. Mine is only 136bhp but on 18" wheels. I am hoping after a good service things might improve a bit. I have the AC on auto set to 20c as well. My temp gauge looks to be around 85-90c ish
So pretty much identical then. Saying that, on the run from mine to Abergavenny today, doing a fairly steady pace in manual mode, I got up to 48. Down to 45 on the way back as it's uphill
 

Bobby Dazzler

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As I was reading the first post in this thread I was expecting to see a truly horrendous MPG figure when I got to the punchline. About 50 MPG sounds about right to me for winter drivinh. Not sure there’s really much wrong.

The difference that traffic conditions, time spent idling, prevailing weather, ambient temperature, use or cruise control, road speed. driver anticipation, cold or warm start, when the trip computer MPG was reset and many other factors all lead to a big variation which makes real world comparison between cars (or even journeys in the same car) very difficult.

Also you shouldn’t expect to achieve published economy figures in real world driving - published figures are to allow comparison between cars rather than set a realistic expectation of what your car will do.

I wouldn’t worry too much unless there are other symptoms.
 
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Seanalf

Seanalf

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As I was reading the first post in this thread I was expecting to see a truly horrendous MPG figure when I got to the punchline. About 50 MPG sounds about right to me for winter drivinh. Not sure there’s really much wrong.

The difference that traffic conditions, time spent idling, prevailing weather, ambient temperature, use or cruise control, road speed. driver anticipation, cold or warm start, when the trip computer MPG was reset and many other factors all lead to a big variation which makes real world comparison between cars (or even journeys in the same car) very difficult.

Also you shouldn’t expect to achieve published economy figures in real world driving - published figures are to allow comparison between cars rather than set a realistic expectation of what your car will do.

I wouldn’t worry too much unless there are other symptoms.

I used to work for VW and Audi, published figures are something I don't expect :Do_O

I get what you're saying, I only asked a the last long run was at 2am to 5am, good conditions, fairly constant (A roads and motorway) with little to no delays. The reset was that morning (from start one). I am gentle with the throttle (I once did from my house to Cobham Services and back on £25 in an Audi A1 diesel!), so I would have thought to get to around 55mpg wouldn't have been unexpected you know. Around here, I don't expect to get much above 40's due to the roads, hills and roundabouts. It's on a run that I expected better maybe?

I'll pump the tyres as per @markjay suggestion, another bottle of Redex and clean the MAF. I'll check the air filter while I'm there too.
 

DrNick

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Has diesel been tinkered with the same as E10?

Winter diesel used to be a thing, and that (and temperature) affects consumption.
 

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