Poor MPG E320 CDI W210

[KLP 92]

I've had a feeling that my MPG wasn't brilliant on my 320 CDI since i bought the car a few months back. I had a few things changed as the car was running badly when i purchased it:

MAS
EGR Valve
Air filter
Diesel filter
Diesel lines
2 injectors
Turbo + actuator
New exhasut, no cats (inc precat), full free flow system.
New hose from intercooler to EGR

My trip computer shows me 38mpg at a steady 80mph, not brilliant but not bad considering the size of the car. I didn't think anything of it until aka$h bought an identical car, same mileage and year build. His car shows 3 mpg more than mine does, both cars doing the came route following each other.

Well, its only 3 mpg, and at this point i should tell you that my car has been Brabus tuned

Now with the Brabus tuning box i shoudl be apparently getting better MPG cruising than stock, but not the case!!

I thought maybe my trip computer was inaccurate so before my trip to Gerrmany i filled the tank and drove a steady 80-85mph to Belgium, economical driving, no sudden bursts of acceleration and no traffic either. Stopped off in Brussels, trip computer stated 38.1mpg. Full tanked the car again and the MPG in reality was significantly worse, 30.2MPG!!

Now 30 MPG cruising at 80MPG is poor for a diesel, especsially when a V12 S Class gave 27.8mpg on the same run last year!! Now that figure is all motorway mileage so i would have expected at least 6-8mpg more, at the very least.

Well i filled the car up on both occasions i made sure the surface was flat to get an even level. I filled it up so i could see the diesel in the filler pipe.

My C270 CDI gave me 46mpg on the same run, i regularly do thhe europe trp so i kno what economy i should be getting.

Now bearing in mind the things i've changed already, what else could be causing me the poor MPG? I had 4 people ion the car, correct tyre pressures, AC off, feather touch acceleration......

Any help will be greatly appreciated or i may just have to buy a E220 CDI

 

[GrahamC230K]

3 mpg could be wheel/tyre size, or model of tyre IMO.

I recently changed a temperature sensor on our VAG TDI to cure a starting issue that also saw our average MPG rise by about 3mpg, so considering the parts you have already changed, a relatively cheap test.

No faults logged it's safe to assume?

 

[maddog]

Thats about what mine does at 80mph fully loaded and has done since it was new mine is Van Aaken tuned and gives a better average economy now than it did before.

I dont think thats bad at all TBH and it still pretty representative of big diesel cars today , from what i have read on here the W211 diesels are worse on fuel than the W210???

I havent double checked my trip computer for a few years though , but i dont think its far off

Either way i'm not complaining as i did a long trip in my Skyline yesterday at motorway speeds i averaged 16mpg

 

[KLP 92]

My main concern is tha my trip computer shows 38mpg when in reality i get 30mpg.

Now i know i have wide wheels etc, but on aka$h's car, when his trp computer says 42mpg he gets 40mpg.

Or are these onboard computers that inccuate? 8MPG seems alot if you ask me! Makes me wonder if there is an point to the if that is the case.

I bought a big diesel engined car because its nice having the power. BUT, when the power means on a motorway i'm only averaging 5mpg more than my S Class then what exaclty is the point?

I could have had the extra luxury of the V12, i took the diesel think i would be getting high 30s, low 40s on a motorway!

 

[KLP 92]

No faults logged it's safe to assume?

Nope, i had everything reset before i left and since i've owned the car its been on diagnostics 10-12 times manily due to a gearbox issue (forgot to mention i had one of them fitted as well!) but nothing else logged.

I thought the consumption has been excessive hence the new MAS and EGR, no difference. MPG remained the same after a service.

Well when i come back later on today i'll refill and recheck the fuel consumption but i'm not holding my breath!

 

[GrahamC230K]

If you are sure about your actual consumption, I would have thought the trip computer can be calibrated in star.

 

[KLP 92]

If you are sure about your actual consumption, I would have thought the trip computer can be calibrated in star.

Yep, full tank before i left and then refuelled and worked out an accurate figure.

30mpg at 80mph just seems low to me!

What i'mgoing to do is swap car's with aka$h for afew days and see what the difference is. The problem is we both to long distance journeys, similar speeds and there is a 3mpg differnce on short tris and 5mpg on long trips. Now bearing in my my trip computer is siginficantly innaccurate then my MPG is alot worse compared to his.

 

[bolide]

Is one car Euro 3 and the other Euro4?

Does that model have the butterflies in the inlet manifold? I have heard of those giving problems & affecting mpg

Nick Froome
www.w124.co.uk

 

[Brian WH]

Is one car Euro 3 and the other Euro4?

Does that model have the butterflies in the inlet manifold? I have heard of those giving problems & affecting mpg

Nick Froome
www.w124.co.uk

Euro 4 didn't come in till the later builds of W211.

I am sure that the 38 mpg is about what I used to get in my old W211 E320CDI on a long run, so the trip mileage is OK. The actual mpg is a worry and needs to be checked on different fuel fills to be sure it was not a fluke reading, or a miss calculation. 30mpg is usually a local trip return not a long run.

 

[DieselE]

Are your wheels standard sizes? This might affect the accuracy of both your odometer and trip computer.

 

[Will]

Just throwing a suggestion into the pool - could your problem be elsewhere - eg, very slightly binding brakes, wheel bearings, tyre type/pressures etc?

Clutching at straws but worth considering if you've exhausted all other avenues

Will

 

[KLP 92]

Just throwing a suggestion into the pool - could your problem be elsewhere - eg, very slightly binding brakes, wheel bearings, tyre type/pressures etc?

Clutching at straws but worth considering if you've exhausted all other avenues

Will

Checked everything, everything seems ok. Tyres checked yesterday before the trip, brakes are ok and wheel bearing were checked by Ollie so deffo ok.

 

[KLP 92]

Update

On the way back from Germany i refueled, reset the trip computer and went back on my way. After 420 miles i refueled and the car took 47 litres. This was driving 90-100mph, so the rough 38.6mpg. Now thats not bad for an old barge! The trip computer was showing 38.9mpg.

Now i put in 60 litres to do 400 miles on the way there so thought maybe when i filled the car previously i didn't put enough in.

On the final leg of the journey i reduced the speed to 80-85mph, i filled the tank and reset the trip computer. After 330 miles the trip computer was on 39.9mpg so i stopped of at the services to check what my real mpg was. filled the car, it took 45 litres and the MPG worked out to 33MPG, even thoough the trip computer stated 40MPG!!

Now i think my problem may either be intermittent or speed/revs related. On the first leg of my return trip i averaged 38.6mpg from 90-100mph driving, on the second leg 33mpg driving 80-85mph. Now who says speeding doesn't pay!

Driving conditions were the same, 4 people, same luggage, AC on, 20-22'C outside. Road conditions/gradients were similar and speed was consistant, no stopping/starting or traffic.

I refuelled to the max each time, as much as i can get in till it begins to overflow

 

[skemball]

This might suggest that the chip tune box on your car is putting more fuel into the engine than is needed for cruising. This would also fool the trip computer as it does not physically measure the fuel flow? My understanding is that it uses pre-set data from the ECU.

Whatever, its worth disconnecting it, obviously your calculations are clearly showing a massive difference to the trip computer.

Mine averages anywhere around 38-43MPG at 70-80MPH.
47-49MPH if driven around 60-65 on cruise.

 

[maddog]

could have a fuel leak of course

 

[se97mlm]

This might suggest that the chip tune box on your car is putting more fuel into the engine than is needed for cruising. This would also fool the trip computer as it does not physically measure the fuel flow? My understanding is that it uses pre-set data from the ECU.

Whatever, its worth disconnecting it, obviously your calculations are clearly showing a massive difference to the trip computer.

Mine averages anywhere around 38-43MPG at 70-80MPH.
47-49MPH if driven around 60-65 on cruise.

Nail on the head I would say. Always said the tuning boxes were rubbish.

 

[timskemp]

You didn't use an google to convert your litres to gallons did you? It assumes american gallons, the one thing that is smaller in the US than the UK...

 

[maddog]

Nail on the head I would say. Always said the tuning boxes were rubbish.

mine is the best thing about my car

 

[timskemp]

mine is the best thing about my car

TBH They aren't all bad otherwise you'd not get MB dealers selling you Brabus ones.

 

[Dieselman]

TBH They aren't all bad otherwise you'd not get MB dealers selling you Brabus ones.

Dunno about that, they sold quite a few bad Mercs, why not a few tuning boxes.

They sell anything that will make them money.