E320 cdi mpg (om642)

[matthew k]

Hi, my car seems to be using more fuel. With the cruise set at 72 (70 actual) mph it averages 39-40 mpg, that's after 50 miles +. I'm sure it used to do 44-45 in the same conditions. AC on or off seems to make little difference. The performance also is maybe slightly down too. About a month ago I added 250ml of Redex diesel to a full tank, could that have damaged anything? Thanks

 

[Craiglxviii]

Mine does 30-32mpg...

AC on or off won’t make a difference as the compressor always runs.

 

[EmilysDad]

...
AC on or off won’t make a difference as the compressor always runs.

a loaded compressor is going to be harder to turn than an unloaded compressor ...

 

[Blobcat]

Mine used to average >48mpg easily, with cruise sat at 76 (actual 73)

 

[dry run]

Hi, my car seems to be using more fuel. With the cruise set at 72 (70 actual) mph it averages 39-40 mpg, that's after 50 miles +. I'm sure it used to do 44-45 in the same conditions. AC on or off seems to make little difference. The performance also is maybe slightly down too. About a month ago I added 250ml of Redex diesel to a full tank, could that have damaged anything? Thanks

Have you put on weight?

 

[matthew k]

Have you put on weight?

No! Well, maybe just a couple of kilos, I've been eating too much bread recently!

There does seem to be big variations in what people get from this engine MPG wise. But it does seem to have suddenly got worse.

 

[Aripeka]

At 60mph mine creeps up to 48mpg on a 30 mile motorway journey. 70mph = 45 mpg. Mixed main road and motorway driving = 40mpg. Once I stayed behind a lorry that was doing just under 60mph and for a short while I got 49.5 mpg.

 

[matthew k]

Was the Redex a bad idea? The car has a diagnostic reading on star, for an unrelated matter, but the guy did a full print out and didn't mention any codes for the O2 sensor.

 

[Uncle Benz]

Binding brake? Low tyre pressures? Worth checking the obvious first

 

[matthew k]

Yes, I will check the pressures. I have checked for brake bind before, but couldn't find any. Plus, performance does seem a bit down.

 

[matthew k]

OK I've just been for a ten mile drive without touching the brakes once. At the end the front discs were tepid, not cold, but you could feel they had a slight warmth. Is that normal?

 

[Blobcat]

OK I've just been for a ten mile drive without touching the brakes once. At the end the front discs were tepid, not cold, but you could feel they had a slight warmth. Is that normal?

later (end 2006 on) W211's have a neat feature in that the pads touch the discs occasionally to clear off water so that they're ready whenever you need them. Not sue on your weather but the system could be drying the discs. I'd also expect some warmth just from the movement (but not a lot)

 

[matthew k]

It wasn't raining, when the cars elevated and the wheels are spun there's a slight drag, I think that's normal. There not binding IMO and the tyre pressures are correct. Sorry to keep asking this, but what's the consensus on my 250ml of Redex?

 

[matthew k]

At 60mph mine creeps up to 48mpg on a 30 mile motorway journey. 70mph = 45 mpg. Mixed main road and motorway driving = 40mpg. Once I stayed behind a lorry that was doing just under 60mph and for a short while I got 49.5 mpg.

Is yours an estate, what size are the rear wheels?

 

[Blobcat]

I've used Redex Diesel in my old VW Caravelle and it improved things (that car did small journeys most of it's life so benefited). My W211 generally did long journeys and never felt the need to put redex or an injector cleaner through it. Doubt it would harm it in any way though.

 

[Craiglxviii]

From a diesel engine design engineer I worked with, "It won't do any harm".

 

[matthew k]

Thanks. The rears are 265/35 18 (unecessarily wide IMO) fronts 245/40 18

 

[Blobcat]

Thanks. The rears are 265/35 18 (unecessarily wide IMO) fronts 245/40 18

I had 245 x 17's on mine, comfortable and economical (also used to get >45,000 miles out of them)

 

[Botus]

my fathers ( same engine v6 3ltr cdi with 7g auto - smaller intercooler and lower boost ? ) does 42 mpg on a run at 70mph

I once saw 44 mpg, but it was painful and one set of lights on red would bring it back to 43 mpg (in a 70 mile drive). Tyre pressures should be circa 33 36 rear, for mildly laden above 70 mph driving

 

[Wighty]

As Botus says , my E320 is pretty much exactly the same as his figures . When I reset on the motorway a while ago I did manage 55mpg but that was 50-60mph for 20 mins