Excessive fuel consumption

[boristhemoggy]

Following a 96,000 mile service by Robins and Day which was not completed, I noticed that on start up the display on the binnacle of my '04 Boxer 2.0 HDI kept saying the oil was high.
I drained a bit out, but some time later my fuel consumption has gone from an average of 28mpg to 15 mpg
I had another garage replace the fuel and air filters but this seems to have had no impact.
Was the high oil the culprit? Or was that a coincidence and is there a common fault for mileage to go down like that?
New pads on the front aren't causing problems, rear wheels aren't hot to touch after driving for a while, and I've tried Redex injector cleaner in the last two full tankfulls to see if it helps but to no avail.
Anyone have any suggestions?

[Peter.N.]

Check the oil level again to see if its gone up, could be fuel leaking into the sump somehow. Either of those fuel consumption figures sound pretty dreadful for a 2.0 Hdi.

Peter

[boristhemoggy]

The oil level has been stable for weeks now.
The consumption hasn't really changed since I bought the van in 2004. It's a motorhome though, so driven at max weight capacity all the time.
If I could get back to my 28mpg I'd be over the moon.

[Peter.N.]

OK, being a motorhome would account for the fuel consumption, the only way you will improve it is to drive more slowly.
The consumption will always increase in cold weather, especially on short journeys but if it performs OK and you have no warning lights or smoke I am at a loss to see a reason.

Peter

[boristhemoggy]

I never exceed 60mph, I drive with fuel economy in mind, always have done. It's bound to go down in cold weather and short journeys as you say, I've known it go down to 25mpg at times, but never know it be this low.
I'm at a loss to see why also, but there has to be a reason. Just filled up, 18mpg since last fill

[spider]

Does seem a bit low but it could be normal but you say it was better and you've had the air / fuel filters changed.

Does it seem "slower" (I know that's a subjective term as its not a speed machine anyway) in any way compared to how it was ? , a blocked cat could cause that.

The only other thing I can think of is a fuel leak somewhere, I thought about EGR faults but that would cause running concerns.

[Bick]

I have a citroen relay 2.0HDI, same vehicle as your boxer and this time of year i get about 35 mpg so your vehicle being a motorhome 28 mpg i would say is pretty good.

The oil high indicator always shows on my relay if the oil level is anyware near the max level mark on the dipstick so i use the dipstick and take no notice of the oil indicator.

The only thing i can think of would to cause such a reduction in mpg following a service would be a fuel leak, my fuel filter is on the n/s of the baulk head and a sod to get to and even worse to get it to seal! other than that are you sure the new pads are not causing the fronts to bind a bit?

[boristhemoggy]

All wheels tested and seem fine. I blame it on new Avon tyres. Never had these before, they weren't that cheap either, but they're a hard compound and have poor grip in wet. Hard to say why, I think simply there isn't another answer and the only thing that's changed recently is the tyres.

[Bick]

you have lost 10 mpg that is far too much to be the tyres.

i wonder if the service has had nothing to do with the problem - you need a diag to just make sure.

[addo]

Misalignment of the front or rear track could cause a decent increase in consumption.

[Peter.N.]

...it will also cause extreme tyre wear.

[evilally]

I'm not familiar with these engines, but does it have something like a MAF or air sensor on the intake? Is it possible they've had this disconnected or fiddled with it when changing the air filter? An incorrect reading here could cause over fueling?

[Peter.N.]

Have you actually checked the consumption by brimming the tank, just occured to me that if this happened at the same time as the oil read high maybe you have an electronic fault giving you a false reading, try disconnecting the battery for a few minutes. I had this happen on a C5 fuel gauge.

Peter