Fuel Economy

[amzchhabra]

for some reason I can't seem to achieve anything more than 38mpg on a 70mph cruise control run, and average around 30mpg otherwise on my CLS320 CDI. Reading these threads, I am starting to think something is wrong...

I had my gearbox oil changed at MB Beaconsfield in October and all was fine with regards to diagnostics. They mentioned during an inspection 3 weeks later that one of my lambda sensors has failed. I checked with my local specialist, who said that if there was an issue the engine management light would come on, but it hasnt, so don't worry about it until it does...

should I get it checked out, would that really be the cause of my low MPG? not entirely sure, but I cant get over 39mpg, I haven't been able to since I purchased the car in September.

 

[DITTRICH]

People place an awful lot of confidence in their trip computers and the electronics to get fuel consumption calculated correctly. Whilst the readouts are fun and informative, a healthy dose of scepticism is required IMHO. Now if someone were to brim their tank, reset their trip computer, use 90% of the tank and then fill up again and compare the trip computer's average mpg to the actual mpg, I might have more faith. Remember the electronics are the weak point in all modern cars. The only really useful part of the trip computer (according to me) is the real time mpg readout which functions as an "economy" readout. Watch the graph go down when your foot meets the carpet. The graph is not 100% real time but is a moving average of around the last few seconds of activity, presumably to stop it jumping around all over the place.
Just my 2c as usual.
Les

 

[kwakdonut]

As we use l/100 km your figures does not mean anything. Is your calculation in UK gallons; 4,55 litre or US gallons?
At 75 miles cruise I got 5,9 l/100 km on the computer however the real figure with brim to brim calculation was 6,7/100 km

Calculations on here will generally be in UK Gallons = 4.546L

This would make your calculations - 1.3 Galls/62 miles (47.7mpg) and brim to brim figures of 1.47 Galls/62 miles (42mpg) - I hope my sums are right!

 

[Shude]

A 45 minute trip down the M6, cruise set to 56mph, all ventillation turned off resulted in 31.5mpg (instrument cluster estimate). Best yet!

The IC is usually within a few decimals of the actual brim-to-brim measurement.

 

[asad7860]

I average about 18mpg from my E55. mainly Urban. Last week I did an experiment where I reset the trip computer on the motorway, whilst travelling at 60mph. I then drove for about 30 miles and averaged 31.7 mpg. I have never seen over 30mpg in this car and was impressed that it could do it. Not that I plan to repeat this exercise!

 

[A210AMG]

With my S211 E320Cdi which was my Dads coming back from Dover with the space saver tyre on doing 56mph all the way back to Cheshire he had 60mpg the range also showed over 1000 miles when he filled up.

Generally he would get 45mpg on almost any run.

Best I have had from my wifes B Class 2.0 Cdi Auto was 58mpg, I've yet to beat 60mpg yet

 

[Mactech]

People place an awful lot of confidence in their trip computers and the electronics to get fuel consumption calculated correctly. Whilst the readouts are fun and informative, a healthy dose of scepticism is required IMHO. Now if someone were to brim their tank, reset their trip computer, use 90% of the tank and then fill up again and compare the trip computer's average mpg to the actual mpg, I might have more faith. Remember the electronics are the weak point in all modern cars. The only really useful part of the trip computer (according to me) is the real time mpg readout which functions as an "economy" readout. Watch the graph go down when your foot meets the carpet. The graph is not 100% real time but is a moving average of around the last few seconds of activity, presumably to stop it jumping around all over the place.
Just my 2c as usual.
Les

I think it's good to sceptical until you have some hard data to support the fuel readout figures. The readouts are driven by a pure calcultation dependent on the injector flow and fuel pressure. In race cars each injector is flow tested and sorted in to batches. In production the flow rate will vary by up to 5%. Then there is the need for a consistent fuel pressure. Most modern cars are capble of maintaining this....but they rely on a fuel pressure sensor may or may not have some error.
I have found the Mercedes V6 diesels to be pretty good in terms of real and displayed consumption, and I have had Honda powered race cars which can drift by 8% for no particular reason

 

[fah320]

Calculations on here will generally be in UK Gallons = 4.546L

This would make your calculations - 1.3 Galls/62 miles (47.7mpg) and brim to brim figures of 1.47 Galls/62 miles (42mpg) - I hope my sums are right!

Yes, it is correct with my calculation

 

[Value Motering]

This is the very best I have had from my CLS 320.
Out of town long runs normally give me about 47mpg if I'm staying close to legallity, but the computer is showing just 42mpg for the last 3000 miles as I have been working very close to home and so doing mainly short trips.

PS. Where did you dig this thread up from!

..
...

Thanks for all the info.

I found this thread just doing a search, no posts in 4 years !!!

As Mactech mentions, CLS320 MPG between 47 and 42 sound just fine to me, brim to brim is they way I check, but have also found total MPG figures worked out by cars to be very close to correct MPG attained.

I guess people get very different MPG's in the same car because people drive in many different fashions, I look ahead and take my foot of the gas when I don't need it, apart from good MPG's, my brakes and tyres last long miles/time.

On a similar note, when I'm going down a big long hill, I keep top gear selected (manual car) and the MPG indicator often gets to 999 MPG prob plus in effect, I know other drivers who take car out of gear as they think it's the best MPG, whick it is not in my understanding and also not the safest way to drive a car.

I will be very happy to drive a CLS and get 44 MPG average, I will hope to report back in the future.

I viewed/test drove a facelift 09 plate yesterday, it was 60k with much paint scratches, but full Merc service history and well specked, inside was immac and drove purfect, it was a local dealers friend, one owner, she was asking 22.5k, I said car was prob worth about 20k due to miles and so many scratches on so many panels, she said lowest price she would accept was 21.5, said I would think about it, but think I would be better waiting for one with less miles and less scratches ???

With the new Reg out soon and the new CLS about to turn up in the UK, I am hoping the older models prices will slide a little down ???

Guess I will keep looking and hope I don't get tempted if I stumble on a very good 520 D Auto.

Another question.... having not driven Auto's for many years, is there any tricks/driving styles to improve MPG ??

And further to previous posts on this thread, I have found my diesel MPG is much better in the summer time and in the winter time when I put a few litres of petrol in a full tank of diesel.

Any info on CLS320/350 cdi most welcome.

Cheers all.

 

[stwat]

Well all this makes for a good read.
But doesn't make me feel any better about the 20mpg urban I get from my w126 300se

My philosophy is, **** the mpg just drive the car and enjoy it