2008 W211 E320 CDi V6 7 speed auto

[chris1200]

Ordinary folk and learned people ... a question.

My car has just turned 100k miles. I use it as a taxi and I turn off the engine when I'm waiting for more that 30 seconds.
I have a relaxed driving style.
I run the gearbox in Comfort mode.
I do quite a bit of town driving, probably 80% of all my driving. My mpg never hits 30. Even on a long run it never hits much more than 35. The car runs faultlessly but the mpg is irritating me. There are no warning symbols on the dash or any obvious indicators that there may be a problem of any kind.
I had an engine oil/filter change about 2000 miles ago and I have started using BP Ultimate diesel over the last 2 weeks but there is absolutely no change whatsoever in fuel consumption. Once a month I chuck in a bottle of Redex injector cleaner and a few times a month I give the car an Italian tune-up on the motorway to clear out any carbon etc. but still no change.
Apart from selling the car (which would break my heart as I love it) what else can I do to help the mpg? I know it's not the most economical engine to begin with and I'm not expecting 45/50mpg no matter what I do to it but how can I maximise the return?
Should I change the glow plugs? Should I change the air filters (2 of them)?
Should I change anything else?

 

[Jobsworth]

Checking the air filters is a good start point. They are undersized for this engine, and clog quickly. Also check your thermostat is operating correctly. The car should run with the temperature gauge 2/3 of the way up. Less than that and it will use more fuel. The other consideration is the lambda sensor. You’ll need to check for fault codes, as it won’t put the light on, but a couple of mpg if that’s dead.
Sadly the v6 isn’t as economical as the older I6. My 2003 320cdi estate will do 38mpg easily and 50 on a decent run.

 

[TeddyRuxpin]

Cold weather and a 2 ton car doing city driving… doesn’t seem too far off what should be expected?

Thermostat would be first port of call for low mpg, PCV after that

 

[chris1200]

Checking the air filters is a good start point. They are undersized for this engine, and clog quickly. Also check your thermostat is operating correctly. The car should run with the temperature gauge 2/3 of the way up. Less than that and it will use more fuel. The other consideration is the lambda sensor. You’ll need to check for fault codes, as it won’t put the light on, but a couple of mpg if that’s dead.
Sadly the v6 isn’t as economical as the older I6. My 2003 320cdi estate will do 38mpg easily and 50 on a decent run.

The temperature gauge runs as it should at 90, I believe this is the optimum level. Everything about the driving of the car is faultless, it may sound as if I have unrealistic expectations but in all honesty I don't. I simply want to get the best out of the engine (OM642).

 

[chris1200]

Are these the correct air filters?

 

[Skd884]

Your mpg is ballpark correct for town driving.

 

[BlackPearl09]

My 280 cdi is roughly 25mpg in the cold weather and town driving. Good weather and a run 44.5 mpg, car runs smooth and well looked after.

 

[chris1200]

Your mpg is ballpark correct for town driving.

Sounds like I may have to live with it and just make sure I do regular maintenance. Is BP Ultimate worth the extra cost?

 

[mbzclk]

Managed 43-46 on a run with the OM642 in a CLK. I think town was anything from 26-33

 

[92Adam]

My E280cdi estate does around 40ish mpg on a very steady run to the in-laws that’s a round trip of around 200 miles all motorway….
Don’t really use it around town but would estimate around 25-30mpg being about right…

It’s a 2007 model with about 187k on the clock…

 

[vijilants]

Sounds like I may have to live with it and just make sure I do regular maintenance. Is BP Ultimate worth the extra cost?

I would use the petrols such as Shell V power which contain detergents, because it will help keep the engine clean, which is fairly essential in keeping diesel in optimum condition. Note that glow plugs won't make the difference as they are only used during the starting process. As above the air filters foul up very quickly on these engines so worth replacing.

I previously owned a C320 cdi which has the same engine as yours and your mpg does sound about right.

 

[MrGreedy]

Trying not to open a can of worms around fuel and additives, but I've been looking at this recently and...

If you can't be bothered with faffing around with 'potions' at the pump, premium diesel with it's better additives package than standard fuel is a good shout.

For the cost conscious, using regular fuel and adding your own additives at fill up is better value. I've been using Redex, but the cost is going up, so I've researched additives more. Something like Archoil AR6900-D appears to be better than Redex, plus it gives you the correct dosing instructions i.e. dose at 1 part in a 1000, rather than Redex 'wang in half a bottle regardless of tank size' type instruction.

Yes, it's £26 (currently) upfront, but if you add e.g. 50l of fuel per fill up, that's 20 doses at £1.30 a pop, which is markedly cheaper than premium fuel. i.e. it's 2.6p premium per litre for this stuff vs whatever premium diesel is over standard?

https://www.amazon.co.uk/Archoil-AR6900-D-Advanced-Diesel-Synthesis/dp/B01IDDF4JM

There are reports in the reviews of (magic?) 6 or 7mpg improvements in economy.

Talking of which (the point of this thread), get out on a reasonably long run on the motorway with engine nice and warm, reset trip computer whilst on the move and do 10 miles at just under 60mph. If you are returning high 40s mpg or better, there is nothing wrong with your engine I'd suggest.

 

[m80]

As said it may well be that you can't expect much improvement.

But worth lifting each wheel and checking there is no binding.
Also as said the oxygen sensor is worth a check. No eml, no codes on Star, but live monitoring and it wasn't responding as it should to pedal action. I replaced it and saw a small improvement.
Yes, the air filters are worth a look.

 

[W1ghty]

Yep , should be early 40’s at motorway speeds for my 2009 E320cdi at 122k now .
My thermostat change a year ago was £34 for the part I think , probably worth doing as preventative maintenance as are the air filters .

 

[TDE1again]

Not helpful, but hope it makes you feel better

 

[boxer 01]

What about this then my 2007 e320cdi sport 160k on the motorway to work steady 65/75mph

 

[W1ghty]

Trying not to open a can of worms around fuel and additives, but I've been looking at this recently and...

If you can't be bothered with faffing around with 'potions' at the pump, premium diesel with it's better additives package than standard fuel is a good shout.

For the cost conscious, using regular fuel and adding your own additives at fill up is better value. I've been using Redex, but the cost is going up, so I've researched additives more. Something like Archoil AR6900-D appears to be better than Redex, plus it gives you the correct dosing instructions i.e. dose at 1 part in a 1000, rather than Redex 'wang in half a bottle regardless of tank size' type instruction.

Yes, it's £26 (currently) upfront, but if you add e.g. 50l of fuel per fill up, that's 20 doses at £1.30 a pop, which is markedly cheaper than premium fuel. i.e. it's 2.6p premium per litre for this stuff vs whatever premium diesel is over standard?

https://www.amazon.co.uk/Archoil-AR6900-D-Advanced-Diesel-Synthesis/dp/B01IDDF4JM

There are reports in the reviews of (magic?) 6 or 7mpg improvements in economy.

Talking of which (the point of this thread), get out on a reasonably long run on the motorway with engine nice and warm, reset trip computer whilst on the move and do 10 miles at just under 60mph. If you are returning high 40s mpg or better, there is nothing wrong with your engine I'd suggest.

I use the Archoil stuff occasionally but for cheap stuff I just use Cetane

2-EHN

Highest quality 99 pure 2-Ethyl-Hexyl Nitrate (2-EHN) cetane improver for raising the cetane value of pump diesel or bio-blended diesel fuels.

www.powerenhancer.co.uk

 

[MrGreedy]

I use the Archoil stuff occasionally but for cheap stuff I just use Cetane

2-EHN

Highest quality 99 pure 2-Ethyl-Hexyl Nitrate (2-EHN) cetane improver for raising the cetane value of pump diesel or bio-blended diesel fuels.

www.powerenhancer.co.uk

I did initially think about using cetane, but I was concerned about the reduced lubricity of fuel caused by the cetane, which is why the stuff like Redex and AR6900-D include additional lubricants as part of the additives, which I would expect the fuel manufacturers to also add.

@W1ghty
have you noticed any difference in MPG using the product (probs not but thought i would ask)?

 

[TeddyRuxpin]

As an ex religious V Power diesel addict, I've switched to getting REDEX from Asda @ £2 a bottle but also noticed that those offers don't seem to come up anymore (now £4). I'd use half a bottle for about £40-50 worth of supermarket diesel.

It's probably still cheaper than V-power @ £4 a bottle, but if I can't find it for £2 I'd probably just use it ever other time rather than every time I add fuel and just live with less cleaning power. My 1/2 bottle every £40-50 is probably overkill anyway.

 

[W1ghty]

I did initially think about using cetane, but I was concerned about the reduced lubricity of fuel caused by the cetane, which is why the stuff like Redex and AR6900-D include additional lubricants as part of the additives, which I would expect the fuel manufacturers to also add.

@W1ghty
have you noticed any difference in MPG using the product (probs not but thought i would ask)?

I’ve used it for so long now it’s not something I ever check . If the car does over 40mpg on runs in sport without sparing the horses that’s good enough for me .
It’s just my way of using premium fuel without paying for it