Reviews The Fuel Consumption Thread

[Mick Briesgau]

The A8 has some serious flaws with its technology. The radar cruise control is very temperamental and is deeply annoying in light traffic on the motorway. It will pick slow moving traffic up from a long distance and apply the brakes for no reason. And this isn't consistent, so it's very difficult to make allowances for it.

Interesting, Betty. I drove a facelifted A8 3.0 TDI Q.4 2013. In that case I was positively surprised by the radar cruise control. At that time it functioned rather well. Not as flawless as in my S-Klasse, but more than okay. What you experienced, was dangerous and is beyond acceptable. Are you considering to complaint or write a letter to AUDI?

 

[Betty Swollocks]

Interesting, Betty. I drove a facelifted A8 3.0 TDI Q.4 2013. In that case I was positively surprised by the radar cruise control. At that time it functioned rather well. Not as flawless as in my S-Klasse, but more than okay. What you experienced, was dangerous and is beyond acceptable. Are you considering to complaint or write a letter to AUDI?

I've driven the 7 Series and S-Class with the radar cruise, and they work far better than the A8. Maybe the A8 you drove was in medium to heavy traffic? The issue I had with it was in very low traffic on the motorway. It would keep picking up a vehicle from a long way in the distance. What is bad is that you can't turn the radar element off, so you either have to use no cruise control at all, or use it with the radar. On the 7 Series at least you can choose whether or not to utilise the radar element. The radar cruise wasn't dangerous. It was just annoying.

The dangerous feature was the collision avoidance. This functions separate to the radar cruise, and in fact you don't even need the cruise activated. It operates at very low speed. It applies the brakes if it thinks you're not going to stop, except it applied the brakes for me even when there was nothing in front (about three seconds earlier there was. The car in front of me did a u-turn, but neither was it particularly close, and he was long gone when the system applied the brakes). I think the system was confused. I didn't tell Audi because I don't think it's going to make any difference. Besides which, unlike the radar cruise, you can turn the collision avoidance off, so if I ever drive an A8 again, I will do so.

 

[Mick Briesgau]

Maybe the A8 you drove was in medium to heavy traffic?

I drove it on Dutch highways, early in the morning and after 6.00 pm on a weekday in autumn 2013. So, yes it was more heavy than medium traffic.

 

[Betty Swollocks]

Mercedes-Benz S 500 4MATIC (W222)

26.3 mpg

10.74 l/100km

Notes:

1) This was a shorter test than I normally do, but it was along my usual test route. It was quite windy but I did a run in each direction. I'm happy that my results are accurate and can be used as "real data".

2) As with all my tests, the figures are measured by driving mostly at 120 km/h (74 mph), and using any "efficient" settings if available. Tyre pressures were verified before driving also.

3) I was hoping for a figure closer to 30 mpg. I would like to try the S 350 BlueTEC to compare it with a diesel.

 

[Betty Swollocks]

BMW 730d xDrive (F01)

41.0 mpg

6.88 l/100km

Notes:

1) This test was along my usual test route. I'm happy that my results are accurate and can be used as "real data".

2) As with all my tests, the figures are measured by driving mostly at 120 km/h (74 mph), and using any "efficient" settings if available. Tyre pressures were verified before driving also.

3) Inferior fuel consumption compared to the Audi A8 3.0 TDI quattros I've tested, but still acceptable IMHO.

4) One thing I noted (and I believe I've mentioned this before), is that the diesel clatter and general noise seemed to be higher than I've experienced before. This was the six-cylinder too. Maybe BMW have removed some of the sound deadening to save weight, but it was very noticeablly "noisy".

 

[Mick Briesgau]

One thing I noted (and I believe I've mentioned this before), is that the diesel clatter and general noise seemed to be higher than I've experienced before. This was the six-cylinder too. Maybe BMW have removed some of the sound deadening to save weight, but it was very noticeablly "noisy".

If memory serves me right, you'll be driving a W222 S 350d (formerly known as Bluetec) in near future. I'm interested in your opinion on this matter in regards of difference between BMW 7er and S-Klasse.

 

[Betty Swollocks]

If memory serves me right, you'll be driving a W222 S 350d (formerly known as Bluetec) in near future. I'm interested in your opinion on this matter in regards of difference between BMW 7er and S-Klasse.

Er, no.

You must have been mistaken. No plans at the moment to drive another S-Class. The opportunity may arise in the future though and I definitely want to get behind the wheel of a diesel S-Class after driving the Twin-turbo V8 last month.

 

[Rolf]

Thanks for the great contribution Betty, very interesting comparison with the 3 uber saloons from Audi, BMW and Mercedes. Okay now I am deviating from the actual fuel consumption thread and focusing on the cars themselves, from your observations while driving all 3 and then comparing them in criteria such as suspension comfort and dynamic behaviour, interior space/comfort/noise levels and the use of the controls and technology included with them, what car would be your preferred choice. If the Mercedes was a 350d then the comparison of engines and powertrains could be included, but I would be keen to hear about your comments for each car.

 

[Betty Swollocks]

Thanks for the great contribution Betty, very interesting comparison with the 3 uber saloons from Audi, BMW and Mercedes. Okay now I am deviating from the actual fuel consumption thread and focusing on the cars themselves, from your observations while driving all 3 and then comparing them in criteria such as suspension comfort and dynamic behaviour, interior space/comfort/noise levels and the use of the controls and technology included with them, what car would be your preferred choice. If the Mercedes was a 350d then the comparison of engines and powertrains could be included, but I would be keen to hear about your comments for each car.

I didn't really drive the S-Class over anything other than a straight road at 120km/h. I was impressed by the quality of the ride.

The 7 Series was superb over the back roads on Saturday. Really nimble, and that was just in "comfort" mode.

The A8 is just bad in terms of the technology not working properly, and overall feeling whilst driving it. It feels like a big A6. The looks aren't great, although this is slightly unfair because the A6's are usually specced in a basic manner whereas the S-Class and 7 Series were specced quite highly.

I can't really comment on the handling comparison because I'm mostly just sat at 120km/h on the highway. The 7 Series I took on a country road and it performed well. (These figures didn't count towards the fuel consumption figures I hasten to add).

 

[Betty Swollocks]

Mercedes-Benz S 350 d (W222)

41.4 mpg

6.82 l/100km

Notes:

1) As with all my tests, the figures are measured by driving mostly at 120 km/h (74 mph), and using any "efficient" settings if available. Tyre pressures were verified before driving also.

2) As with my experience of all MB cars, the on-board computer wasn't as accurate as BMW or Audi.

For comparison, here is the data I recorded for rival cars.

Audi A8 3.0 TDI clean diesel quattro (D4)
45.8 mpg (UK)
6.17 l/100km

Audi A8 L 3.0 TDI clean diesel quattro (D4)
46.3 mpg (UK)
6.10 l/100km

BMW 730d (F01)
44.5 mpg (UK)
6.35 l/100km

BMW 730d xDrive (F01)
41.0 mpg (UK)
6.88 l/100km

 

[Mick Briesgau]

Mercedes-Benz S 350 d (W222)

41.4 mpg

6.82 l/100km

Notes:

1) As with all my tests, the figures are measured by driving mostly at 120 km/h (74 mph), and using any "efficient" settings if available. Tyre pressures were verified before driving also.

2) As with my experience of all MB cars, the on-board computer wasn't as accurate as BMW or Audi.

For comparison, here is the data I recorded for rival cars.

Audi A8 3.0 TDI clean diesel quattro (D4)
45.8 mpg (UK)
6.17 l/100km

Audi A8 L 3.0 TDI clean diesel quattro (D4)
46.3 mpg (UK)
6.10 l/100km

BMW 730d (F01)
44.5 mpg (UK)
6.35 l/100km

BMW 730d xDrive (F01)
41.0 mpg (UK)
6.88 l/100km

Interesting, for me unexpected result. Comparison is useful. Thanks for your effort, Betty

 

[Betty Swollocks]

Audi Q7 3.0 TDI quattro (272 PS) (7 seats) (4M)

36.0 mpg

7.85 l/100km

Notes:

1) Unlike all my other fuel figures in this thread, this test wasn't performed at a constant 120km/h. It did involve some driving at sustained speeds of around 140-160km/h, and also in town driving. However, from a casual observation, I suspect a figure of around 36-38 mpg would be expected when cruising at 120km/h.

2) The Q7 was impressive. The size and weight (strangely), only became noticeable at lower speeds as opposed to higher speeds.

 

[Betty Swollocks]

I decided to display all of my fuel consumption tests in one table. As always, the fuel figures have been attained by following strict methods which are as follows:

* Tyre pressures checked beforehand using a very accurate digital tyre pressure monitor.
* Windows always up.
* Driven in the same manner and along the same route.
* Cruising at 120km/h (74mph).
* Any efficiency programmes the car has are used, such as "ECO PRO" for BMWs.
* Fuel tanks are brimmed at the start, and brimmed at the end, and then verified. The on-board fuel computer is not used.
* I always use standard fuel. 95 octane in unleaded cars, and standard diesel in diesel cars. In high-performance cars I use high octane fuel (99+).
* Any outside influences such as headwinds/tailwinds, standing water, then the results don't count and are not included.

* Edited to include l/100km and U.S. mpg figures.

 

[Centurion]

^^
That's good fuel consumption for the Q7. However it's known that diesels prove their worth at motorway speeds over long distances.

I mostly drive on urban roads, but as soon as I have spent 30min on the motorway the MPG climbs.

 

[Rolf]

Thanks for the table Betty it makes interesting reading and comparisons. The F30 320d models you drove, was the one in 2013 the 1st gen with the older 184PS engine and the one in 2015 the FL version with 190PS engine? Surprised the older car was more fuel efficient, although its a minor difference.

My E90 320d 6speed AT is one of the older 2005 models with 120kw (163PS), but it still delivers excellent fuel consumption on the motorways, if I set the cruise control at 120km/h it gets an indicated 5ltr/100km. On long trips from Joburg to Cape Town (1450km one way) with a mix of uphills and downhill mountain passes set the cruise control at 130km/h I got an average of about 5.5ltr/100km. In town driving it rises to about 8 to 8.5ltr/100km, not bad for an 11year old car.

 

[Betty Swollocks]

Thanks for the table Betty it makes interesting reading and comparisons. The F30 320d models you drove, was the one in 2013 the 1st gen with the older 184PS engine and the one in 2015 the FL version with 190PS engine? Surprised the older car was more fuel efficient, although its a minor difference.

Yes they were. I think the reality is that they're both very close, and in fact minor differences such as temperature and wind speed may skew the results. It's impossible to make every test exactly the same. Interesting none the less.

 

[Mr Robert]

I cry when I see these numbers.

 

[Betty Swollocks]

Updated fuel table based on a 120km/h cruise. This is after I tested the Mercedes-Benz S 350 d (W222) with the 9-speed 9G-TRONIC auto instead of the 7-speed auto.

There was definitely an improvement, unsurprisingly. Yet again though, the on-board computer figures were a lot more optimistic than the reality.

I've highlighted both cars in red.

 

[Mick Briesgau]

Thanks Betty! 0,64 liter less diesel on 100 km is quite an achievement, if we're talking about the only difference between the two cars you've driven, is the automatic gearbox. Do you remember if the tyresize was the same? If I',m not mistaking both cars you drove had 18" wheels. Those rims come with either 4 x 245/50 tyres or with two 245/50 front tyres and two 275/45 rear tyres.

 

[Monster]

Updated fuel table based on a 120km/h cruise. This is after I tested the Mercedes-Benz S 350 d (W222) with the 9-speed 9G-TRONIC auto instead of the 7-speed auto.

Do you remember the engine rpm at that speed for both cars?