Citroen C5 X7 - 2.0 Hdi 138hp - MPG

[andyhugill]

Hello All,

I have had a C5 X7 2008 estate, 2.0 Hdi version, for about 6 months now after owning a Mk2 C5 for ten years previous to that. Overall i'm very happy with the car, i've had to spend a fair bit replacing parts (rack, front lower wishbones, suspension pump) but i did get it for a good price for a high mileage car.

Traveling 50 miles each day for work I've always been getting 46mpg but since changing the suspension pump a few weeks ago it's down to 41mpg. This i assume is just a coincidence since the suspension pump should have nothing to do with the consumption, i set the height manually by adjusting the height sensors and it is about right. About a month ago i cleaned out the air manifold and egr pipe as the manifold was caked up with gunk from the egr but the consumption was still good after this. Cleaning out the manifold stopped the stuttering at 2k rpm and the odd ecu light coming on and the engine has since been running really nice.

Has anybody got any ideas why the consumption has dropped, is it worth getting the car chipped or should i try and find the problem first. I'm thinking it may be the injectors but don't want to spend any more money until i have a better idea.

Thanks.....Andrew

[Peter.N.]

I would suspect that it coincided with a sharp drop in temperature, the winter chill knocks about 5 mpg off our 406's.

Peter

[MikeT]

And don't forget, we're supplied with "winterised" fuel now.

[GiveMeABreak]

Yes - here's an article on it:
http://www.dieselcar.com/features/docto ... l-economy/

[Peter.N.]

Interesting that Marc. My first 406 estate used to average 50-60+mpg, maybe a little less in winter, the two I have now are doing 40-50 mpg at the moment within about 1 or 2 mpg of each other, I have checked or changed everything I thought relevant with little or no effect, the only thing I haven't tried are the injectors so I have just ordered a set of seals and will fit the ones from my first car which is languishing in the field.

If that makes no difference I can only surmise that the fuel computer and/or the speedo/milometer was inaccurate on my first one. I will let you know.

What I did notice with the first one was that the fuel consumption was much heavier when the engine was cold, even in the summer, although we were in Scotland when I checked it, probably by 10 mpg, the present ones may be the same of course, I haven't checked them.

Peter

[Paul-R]

I distrust the computer MPG readouts and I base all my MPG results on full tank to full tank calculations. Having said that the readouts from both the X7 and 308 do tally very well with my workings out.

I have read elsewhere that if your calculated fuel consumption doesn't closely match the computed figure then it's very, very likely that the injectors are at fault.

[Peter.N.]

On the present cars I have checked the mpg figures with the brim to brim method and the readings are not too different but of course that is assuming that the tachometer is accurate. I know I could get 1000 miles on a tankful from the first one but was the 1000 miles accurate.

Peter

[Michel]

Yes - here's an article on it:
http://www.dieselcar.com/features/docto ... l-economy/

I don't trust anyone who's answer is to use Millers EcoMax to try and resolve a problem!

I've no diesel car to try it in now, but I wonder if using the Ultimate/V-power etc diesel causes the same issue in winter? Using that would be cheaper than using Millers too!

Using the OP's figures on a theoretical 60 litre fuel tank ;

46mpg - 607 miles (summer diesel)
41mpg - 537 miles (winter diesel)

At the price diesel is over the road from here, that works out at a "loss" of £9.40 per tank full. A bottle of Millers is more expensive than that. I'd be tempted to use V-power or BP Ultimate diesel and see if there is a difference. I use Shell V-Power PETROL in my Focus because of it's state of tune.

[GiveMeABreak]

The cleaners in the V-Power and 'Super Diesel' fuels apart from their 'performance' attributes, when used regularly will keep the injectors clean as well as the other fuel components - so adding STP diesel cleaner or similar is not really needed if using these regularly. The winter fuel changeover is usually done automatically - here's an extract from the UK Petroleum Industry Association:

During very cold weather some diesel-powered engines may experience difficulties with starting. These problems arise from the formation of wax crystals, which block fuel filters and lines.

• UK diesel is manufactured to the European standard BS EN 590 and the specification of diesel is changed during winter months (16th November to 15th March) in order to improve cold weather performance properties of the fuel.
• The UK is in a zone that specifies that diesel remains free of wax crystals down to minus 15 degrees Centigrade (known as the cold filter plugging point test CFPP)
• With sustained temperatures below this level, particularly in exposed areas or when a vehicle is left idle for several days, blocking of filters or fuel lines may occur making it difficult to start the vehicle.

And in addition, there are other factors that will contribute to reduced MPG:

Colder air is denser, which can increase the vehicles drag factor; winter Diesel can have less 'energy' per gallon than normal and tyre rolling resistances will decrease from reduced pressures in colder months. And not forgetting the increased use of heating and other electrical devices.

[Peter.N.]

Once we had experienced 'waxing' problems in the olden days we used to add a gallon of petrol to a full tank of diesel, that usually cured it.

Peter

[MikeT]

A bottle of Miller's treats 10 (50L) tankfulls and works out cheaper than V-Power (which I've sworn by since my petrol days).
As an experiment, I swapped to regular diesel and began using Miller's instead, though have been double-dosing.
The results were positive, smoother running, good mpg and the reknowned 2k flatspot was all but eliminated (ie, barely detectable).

However, after my last refill, including Miller's, the initial 30mile drive after was as normal, (in fact saw my highest ever temporary mpg of 64.7) but that all changed the next day.
Aside from losing the smoothness, the hesistation flatspot is returning and the mpg has dropped. Hello winter!

[Sloppysod]

................ although we were in Scotland when I checked it, probably by 10 mpg, the present ones may be the same of course, I haven't checked them.
Peter

Hi Peter, I know some think these are is not needed in the UK, but I fit one of these when the ambient temperature drops below 10 degrees for over a week (November ish) and then take it off again when the temperature rises again (March/April). It does help with warm up and keeping the road salt away from my radiator and helps the mpg.

GMB - The part number is 7429G7 - Screen info -

[Peter.N.]

That's interesting, didn't know such a thing was available.

Peter

[GiveMeABreak]

One of my earlier cars (can't remember now whether it was the XMs) had a sliding part that you could use in winter to keep some of the colder air out.

These additional grilles on the X7 are referred to as a snow guard - mainly intended for use in the colder snow-bound countries (note the "Very Cold Countries") proviso on the parts description - as you wouldn't want to fit and forget to remove it. This from the manual:

£32.58 Inc. (7429 G7)

[Sloppysod]

These additional grilles on the X7 are referred to as a snow guard - mainly intended for use in the colder snow-bound countries (note the "Very Cold Countries") proviso on the parts description - as you wouldn't want to fit and forget to remove it.

That is the one of the reason I have only bothered with the lower (bigger) guard, and never ever had any problems with over heating, even siting in traffic, and my car has the front engine under tray intact.