Fuel Consumption

[littlebrooklyn]

Yesterday we drove over to Surrey on the wonderful M25, which thankfully was fairly clear and we maintained an average speed of 70mph apart from the few miles where they are widening the road where the speed limit is 50mph. We did a total of 112 miles but returned a fuel consumption of only 36.5mpg.

On the Autotrader site it gives the A170 fuel consumption as 32.8mpg urban, 51.4mpg extra urban and 42.8mpg combined. We had the auto box set in Comfort not Sports mode and we were quite disappointed at how much fuel we used.

Our previous C200K Estate gave us about 43mpg on the motorway, so we are a bit confused as to why the A Class seems so thirsty

 

[Alex M Grieve]

Yesterday we drove over to Surrey on the wonderful M25, which thankfully was fairly clear and we maintained an average speed of 70mph apart from the few miles where they are widening the road where the speed limit is 50mph. We did a total of 112 miles but returned a fuel consumption of only 36.5mpg.

On the Autotrader site it gives the A170 fuel consumption as 32.8mpg urban, 51.4mpg extra urban and 42.8mpg combined. We had the auto box set in Comfort not Sports mode and we were quite disappointed at how much fuel we used.

Our previous C200K Estate gave us about 43mpg on the motorway, so we are a bit confused as to why the A Class seems so thirsty

Hi Lyn,

That does seem poor. Cold weather certainly has an effect, but most pronounced on short journeys with a cold engine. "Average 70 mph" indicates that the cruising speed must have exceeded that for parts of the journey, as it is difficult to keep up to 70 in mixed traffic, so more oomph is needed to get the average back up.

If the overall figure you quote is from the dashboard display, that can vary a lot depending on the traffic conditions, although slowing to 50 for road works usually has a disproportionately beneficial effect.

I would do brim to brim fills for a few tanks, noting the total mileage.

Fill the tank and zero the trip. Have several tanks full and then finally brim the tank after all those and note the trip mileage. Litres x .22 gives gallons. Divide the trip mileage by the derived gallons figure. Then you will know more accurately.

Fingers crossed that you will get a much more palatable result.

112 miles is a "small sample" and can be significantly influenced by some of these factors. The bigger the sample (1,500 miles perhaps) the less volatile the calculation and the more reliable the result.

 

[television]

You need to go on a diet Lyn

 

[Alex M Grieve]

You need to go on a diet Lyn

Steady Malcolm, her wet weight is only 2/3 of what Andy has lost so far!

 

[littlebrooklyn]

Well Keith says he's noticed the mpg hasn't been very good since we got the car. The display yesterday said we were doing an average of 51mph and apparently 56mph is the 'optimum' speed

I know on previous times when we've done exactly the same trip at a similar time of year when it's quite cold in the C Class that we definately got a much better mpg, yet it seems to make no sense

 

[st4]

Is the A class a petrol engine?

 

[SQ_W211]

I believe it is a petrol engine.

Few things to check Lyn - Make sure the tyre pressure is what its suppose to be ( I gained 2mpg by just filling them according to the specified level)

Also try to use injector cleaner with 1 full tank and see if you see any improvement, I usually notice significant power and economy gain with good Wynn's injector cleaner.

 

[television]

Steady Malcolm, her wet weight is only 2/3 of what Andy has lost so far!

I know,,she keeps herself in very good working order.

Lyn just a thought,what temp is the engine getting up to

 

[wemorgan]

The A-class is quite a tall car, so I suspect efficiency drops away quickly with high-ish speeds. Smooth driving is also very important. The M25 can be very variable in speed, so if you simply copy the car in front you're likely to be accelerating-decelerating often.

 

[littlebrooklyn]

Is the A class a petrol engine?

Yes it's a 1.7 petrol engine.

I believe it is a petrol engine.

Few things to check Lyn - Make sure the tyre pressure is what its suppose to be ( I gained 2mpg by just filling them according to the specified level)

Also try to use injector cleaner with 1 full tank and see if you see any improvement, I usually notice significant power and economy gain with good Wynn's injector cleaner.

Tyre pressures are correct apparently, although I am getting 2 new tyres next week, but I guess that won't make any difference.

As you can see from my signature Keith's company makes fuel injector diagnostic testing machines, so when he has time I guess he could pop the injectors into one of the machines and see if that helps

I know,,she keeps herself in very good working order.

Lyn just a thought,what temp is the engine getting up to

Engine temp is between 86 and 88 I think, not sure if that is right or not :lol:

 

[littlebrooklyn]

Hi Lyn,


Fill the tank and zero the trip. Have several tanks full and then finally brim the tank after all those and note the trip mileage. Litres x .22 gives gallons. Divide the trip mileage by the derived gallons figure. Then you will know more accurately.

Fingers crossed that you will get a much more palatable result.

112 miles is a "small sample" and can be significantly influenced by some of these factors. The bigger the sample (1,500 miles perhaps) the less volatile the calculation and the more reliable the result.

We just filled up today, having done 287 on one full tank and we used 44.51 litres and the result we got is 28mpg, which is even worse than we thought

 

[television]

Nothing wrong with the engine temp then Lyn

 

[turbopete]

when i had some work to go to, the drive between carlisle and silloth where i was working at the time, driving at sensible speeds, my 1.7 puma returned an average of 35mpg. this included thawing the windscreen every day etc! ive since bought an ice scraper to reduce fuel consumption a little!

 

[hawk20]

On a run, you can almost always get the combined mpg figure on every MB I've tried. So your A class should be able to return about 42 mpg on a run. BUT to get that you cannot average 70. You need to use 70mph as your cruising speed. And if your husband drives and is used to a more powerful car he may well put his foot down more than is necessary or desirable if economy is your goal. Especially if you drive in the Comfort setting with the auto box as he will press even more to get his desired oomph.

Accelerating hard hugely reduces mpg. When I am trying for economy I try never to push the accelerator down more than 25mm (1 inch). Get there just about as quickly but use a lot less fuel. (Not so much fun though).

Going over 70 greatly increases fuel consumption.

You need to do tankful at the beginning of a long run (and reset the trip) and then fill up immediately afterwards to get any fair idea. The petrol used for the miles done is an accurate measurement.

 

[Dosco]

..on that score you are somewhat behind my old petrol 2.4Ltr barge at 36mpg, has to be driving style or perhaps change it for a C class :lol::lol:

 

[roadhog]

From hawk20's post it's quite clear that under 'normal' driving you won't be seeing the manufacturers claimed figures. That doesn't explain why an A class should be worse on fuel than your previous C. I take it that you haven't changed your driving style with the new car?

 

[littlebrooklyn]

From hawk20's post it's quite clear that under 'normal' driving you won't be seeing the manufacturers claimed figures. That doesn't explain why an A class should be worse on fuel than your previous C. I take it that you haven't changed your driving style with the new car?

This is exactly our point, the car is being driven exactly as the C Class was and the C Class was a bigger heavier car with much more oomph than the A Class. At this rate Keith may as well be driving the Boxster all the time as the fuel consumption on that isn't that far behind

 

[twistedsanity]

On a run, you can almost always get the combined mpg figure on every MB I've tried. So your A class should be able to return about 42 mpg on a run. BUT to get that you cannot average 70. You need to use 70mph as your cruising speed. And if your husband drives and is used to a more powerful car he may well put his foot down more than is necessary or desirable if economy is your goal. Especially if you drive in the Comfort setting with the auto box as he will press even more to get his desired oomph.

Accelerating hard hugely reduces mpg. When I am trying for economy I try never to push the accelerator down more than 25mm (1 inch). Get there just about as quickly but use a lot less fuel. (Not so much fun though).

Going over 70 greatly increases fuel consumption.

You need to do tankful at the beginning of a long run (and reset the trip) and then fill up immediately afterwards to get any fair idea. The petrol used for the miles done is an accurate measurement.

disagree strongly with that, fuel expands as temperature increases, brim to brim is not accurate at all

 

[roadhog]

This is exactly our point, the car is being driven exactly as the C Class was and the C Class was a bigger heavier car with much more oomph than the A Class. At this rate Keith may as well be driving the Boxster all the time as the fuel consumption on that isn't that far behind

That sounds as good an excuse as any to drive the Porsche. I just hope you didn't trade the C for economy reasons? How long until the next service is due? I'm thinking that sparkplugs, air filter etc below par may well adversely affect your fuel consumption

disagree strongly with that, fuel expands as temperature increases, brim to brim is not accurate at all

I'd have thought that would be negligible for all but scientific tests.

 

[Dosco]

disagree strongly with that, fuel expands as temperature increases, brim to brim is not accurate at all

It works for me and having no electronic wizardry it is the only method I can use. Best though if you carry out such a test on one long journey and do that two to three times that will even out any minor inaccuracies such as fuel expansion/contraction.

Being a old git I tend to do this form of measurement quite frequently and (more or less) achieve the same consumption figures.