mpg

[tupac2makaveli71]

hey guys, i own a c220 cdi sport coupe 2001, and im only getting between 21-28 mpg on average, now for a diesel that cant b good, i dont rag the car i drive normally and i even tried fuel cleaner,any suggestions?

 

[T1M4]

No that doesn't seem right i have a 1999 C220 CDI and i get 44 mpg i would like to know if anyone has any ideas for you!

 

[jberks]

are you getting lots of black clouds out of the back?
Does it start ok?
How is the performance?

Also, is it an auto and what traffic and road conditions do you drive on mainly.
London city traffic and a healthy c220 could return those figures quite easily. (I've seen 23 out of my E270 - but I've also seen 48 )

 

[panason1c]

hey guys, i own a c220 cdi sport coupe 2001, and im only getting between 21-28 mpg on average, now for a diesel that cant b good, i dont rag the car i drive normally and i even tried fuel cleaner,any suggestions?

First thing to check is the condition of the air filter.......a restricted air filter can dramatically increase fuel consumption.

 

[tupac2makaveli71]

just been serviced, sometimes blows some smoke but performance isnt lacking at all, and yeah i live in traffic central!
sorry about the late reply i just got back from the states!

 

[tupac2makaveli71]

and it starts up real quick

 

[jberks]

Well sitting London traffic, a large proportion of the fuel used is just to keep it idling. Very little is used for forward motion and when it is, it's got to get it moving from stationary. In those condiions 21-28 is ok really. As I say, my E270 can get into the low 20s and that's assuming at least a short dual carriageway blast to improve the average. In conditions like central London I'd expect to get into the teens.
You need to get it on a run and see what it does.
I remember looking at the mpg on my E240 once after a queuing in traffic for most of a 6 mile journey - 13mpg!

 

[C240yaz]

First thing to check is the condition of the air filter.......a restricted air filter can dramatically increase fuel consumption.

Agree, Check the airfilter first. Just because it has been serviced, does not mean a new filter was fitted. check it anyway just in case.

 

[citroennut]

hi,
it's unfortunate but good to hear i'm not the only one! i have had this problem as well, car checked out ok, but on tank to tank fills got 33mpg combined and this inc. some runs. there was also a booming between 1000 and 1500 rpm on overrun as well as steady speed, check out post for booming noise. problem still not resolved but mercedes aware of problem now, but lack of fault codes means there is no problem! aye right
simon

 

[RFdesigner]

I've done a simple test on mine that reveals just how much fuel it takes to keep the engine moving.

I use the mpg computer and make sure it covers about 10 miles, more miles means better accuracy but a longer test to get decent results.

Lets say it says 30mpg.

Now whilst stopped and in neutral of course, I rev the engine to the speed needed to run at, say, 70mph, in my case about 2050rpm.

I then time the changing mpg on the dash.

Lets say we drop from 30mpg to 29mpg in 30 seconds and we have 10 miles recorded

Now a bit of noddy maths.

1., start, 10 miles at 30mpg = 0.33333 gal
2., end, 10 miles at 29mpg = 0.34483 gal

2-1 = 0.0115 gal in 30 seconds

equivalent to 3600/30 * 0.0115 gal/hour

at 70mph we have 70 / (3600/30*0.0115) mpg

Which drops out at 50.75mpg.

If you got this I'd be worried, I get well over 60mpg doing this and I have a 320CDi

regards

Derek

 

[tupac2makaveli71]

well im stumped!

 

[RFdesigner]

I assume your talking about my post.

The idea is to see just how much fuel is being used to keep the engine running when at speed. If you're getting duff mpgs there could be any number of things going wrong, from driver inputs to traffic to wind direction to hills to blocked air filters.

By running an 'in neutral' test you can completely eliminate poor road conditions, poor driving, under inflated tires etc. It should be repeatable, and consistent across vehicles. You can even run the test with and without alternator loads or air con to see what sort of impact these have.

All your left with is what's underneath the bonnet. If you get a good number then it's probably not worth spending hours on end trying to locate a faulty engine component, as there probably isn't one.

Derek

 

[C240yaz]

I've done a simple test on mine that reveals just how much fuel it takes to keep the engine moving.

I use the mpg computer and make sure it covers about 10 miles, more miles means better accuracy but a longer test to get decent results.

Lets say it says 30mpg.

Now whilst stopped and in neutral of course, I rev the engine to the speed needed to run at, say, 70mph, in my case about 2050rpm.

I then time the changing mpg on the dash.

Lets say we drop from 30mpg to 29mpg in 30 seconds and we have 10 miles recorded

Now a bit of noddy maths.

1., start, 10 miles at 30mpg = 0.33333 gal
2., end, 10 miles at 29mpg = 0.34483 gal

2-1 = 0.0115 gal in 30 seconds

equivalent to 3600/30 * 0.0115 gal/hour

at 70mph we have 70 / (3600/30*0.0115) mpg

Which drops out at 50.75mpg.

If you got this I'd be worried, I get well over 60mpg doing this and I have a 320CDi

regards

Derek

You cannot judge MPG by this test. Any engine tested by this method will always show exeptional MPG. There is no load on the engine while doing it this way.

This is similar to comparing Horse power of an engine to Brake horse power at the drive wheels. Significant difference.

 

[JEZ.S320L]

You cannot judge MPG by this test. Any engine tested by this method will always show exeptional MPG. There is no load on the engine while doing it this way.

This is similar to comparing Horse power of an engine to Brake horse power at the drive wheels. Significant difference.

Nor any wind resistance!

 

[jberks]

Whilst the above is true to some extent, the basic rule is still that the fuel has to go somewhere. Assuming it's not pouring out of your fuel filter, and your injectors aren;t spraying it out of the head, then its' going through the engine.
If she's running a bit rich, the telltale on a diesel will be over regular stick black clouds and a high CO reading. Clouds admitteldy could be tricky to detect but the CO is a doddle for most garages to check and would probably have shown up on the service. Certainly it would show up on an MOT and it's a cheap enough test to have done.

That said, given where you live and drive, I still don't feel that your mpg is too far out. Sure there are people who'll tell you they get 50-60mpg but dig a little deeper and you'll find the do a steady 60 through the Lincolnshire flatlands, outside rush hour. Remember at that rate, the engine will be basically just above idle (using the same fuel flow rate as you are sitting in traffic), but he's getting 1mile per minute for his whilst you're getting 50yds.

Plus, Inertia is your enemy. Any acceleration uses vastly more fuel than cruising and you spend probably 80% of your time accelerating and the other 20% braking. Every time you brake, you turn that fuel you just burned into plain old heat, rather than momentum.

This is why hybrids make such sense in town. Braking energy is captured rather than blown into the wind and recycled into momentum when you need it, plus the engine isn't turning when you don't need it to. However, at cruise, it's worse as you have the extra weight of the kit to haul up hills, but no wasted energy for it to recapture.

If you're concerned, get a CO test done, but I suspect all is fine.

 

[television]

My V70R averaged 25.7 in Herts, down here in Dorset it does 20,5

 

[Glenn Smith]

I would not be happy with these figures, my van gets the pants thrashed off of it and i get 35mpg quite easily, ok town driving is hard on mpg but the worst i saw was my old peugeot 406 which did 20mpg over a tank full (town driving only) but could achieve 38mpg on a fast long run (ie 70-90mph) this was a 2ltr petrol, ok so my jag is very thirsty, but it weighs 1800kg has a 3.2ltr petrol engine and i do short runs quickly but i still get 20+mpg. and the C230K i get around 28mpg, one thing i would do is check the figures manualy, rather than use the fuel computer and also check the mileometer against another vehicle, if thats ok check your speedo is accurate as well.

 

[RFdesigner]

You cannot judge MPG by this test. Any engine tested by this method will always show exeptional MPG. There is no load on the engine while doing it this way.

I'm not trying to judge the entire vehicles MPG

What I'm trying to do is identify where the energy is going.



lets turn our MPG on its head and call it GPM, gallons per mile, it might be easier to think of that way

Now lets say I get 0.05 gallons per mile and you get 0.02 gallons per mile.

ok, my car looks thirstier but that could be traffic wind under-inflated tires etc. so I run the 'in neutral test' and get 0.02 gallons per notional 'mile'.

ahh there's something wrong, mine drinks as much as yours but with no load!

of course if I'd achieved 0.005 gallons per mile then there may not be anything wrong, I just drive badly/ live in a congested area/ don't inflate my tyres etc. etc.. a whole heap of alternative explanations that have nothing to do with problems under the bonnet.

Derek

 

[jberks]

I kind of get the maths - not entirely convinced it can be accurately measured this way, partially as the MPG reading on the computer are rarely that accurate and partially as you'd need a much larger sample to have a hope of accuracy. To be honest the only way I could see it working would be to brim 2 cars, then leave them parked at the pumps ticking over for 60 minutes then re-brim.

I still reckon that 21-28 is ok if it's heavy traffic. Out of curiosity, what does the computer show as average speed? Also what tyres do you have? Wider ones can cost mpg too.

I noticed the old man's E220cdi showing 22mpg a few weeks ago, but he'd been ferrying my mum around the shops so stop/start/traffic and on/off/idling in car parks whist she nipped in somewhere or other. The car is fine - he got 48, 5 up and luggage on a run a week or so after.

Do check your tyre pressures (can make a big difference), put it on an incline in neutral and ensure it rolls so no brakes are binding, check for any leaks and finally get a CO2 test done. If all ok - then it's fine.

 

[C240yaz]

I'm not trying to judge the entire vehicles MPG

What I'm trying to do is identify where the energy is going.



lets turn our MPG on its head and call it GPM, gallons per mile, it might be easier to think of that way

Now lets say I get 0.05 gallons per mile and you get 0.02 gallons per mile.

ok, my car looks thirstier but that could be traffic wind under-inflated tires etc. so I run the 'in neutral test' and get 0.02 gallons per notional 'mile'.

ahh there's something wrong, mine drinks as much as yours but with no load!

of course if I'd achieved 0.005 gallons per mile then there may not be anything wrong, I just drive badly/ live in a congested area/ don't inflate my tyres etc. etc.. a whole heap of alternative explanations that have nothing to do with problems under the bonnet.

Derek

it does not not work that way. Believe me. Ask any trained vehicle tech and I am sure they will agree. If you put the engine under load, it will use more fuel. That goes for all engines, petrol and diesel.