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Could it be worth putting the standard wheels on for a tank of fuel just to make sure it's not that. Then go back to the dealer

This may sound a really naive question but could the adblue be affecting it? Is there different grades of adblue? I know it’s only water and urea mixed but not sure about it!

Wide wheel do affect fuel consumption, especially heavy ones, but won't be that much like in your case. Also could be your driving pattern, if you do alot of short trips. Could be combination of both of these factors. These engines take forever to heat up to the full temperature. I had a brand new van with same engine for a day, while mine was serviced. Took about three times longer to heat up, than my petrol engine on the same run. If I had a diesel, I would be running cold engine for most part of my 7 miles journey to work.

The mileage was recorded over 3 separate motorway journeys of 330 miles each (165 each way from home to work) I live 1 mile from the motorway. There is no gear change for at least 154 miles and a constant speed of 70mph. I let the cruise control do the accelerating so I would say the driving style is very conservative. No hard accelerating!

Ok. Because of time constraints. I’ve got it booked on to a rolling road to tell me true power output but can’t get it done till 21st December. To me there is a definite power loss so I guess this will tell me if I’m write won’t it?

So the van was put on a rolling road yesterday. Before the guy even started the engine he said "I bet you have problems with acceleration"! Turns out that the 19" wheels that are on the van have thrown the gearbox ratio out by so much its scary. He told me to measure the circumference of the tyre and compare to the original 15" wheels. Out of the 4 runs he did on the rolling road, they all came back the same...... 114.6 bhp (98bhp at the wheels). The van is the 102ps engine. Has anyone else had the problem? Can anyone tell me the outer circumference of a 15" wheel/tyre to compare?

My factory fitted alloys and tyres are 205/55/16 ET50, width 6.0"
You can use this website https://www.willtheyfit.com to compare it with what you have, including circumference.

Cheers Giddy. I looked at the site/link earlier this morning. Not a massive difference in size so I can't figure out where the big loss in fuel and acceleration has gone!

I wonder if you are chasing a ghost? My mid range 2.0 maxi 4Motion delivers around 42-44mpg routinely climbing up and down from a ski resort in the Alps with 7 occupied seats, masses of luggage and a full roof box. Performance is far less on shorter trips during mid-winter when it takes ages to get up to temperature and heated seats etc are working overtime - it is a lot better on occasional cross continent runs in summer.

There is of course a big difference between mpg figures in a sales catalog and real world performance.

You might want to have a read of this assessment by Honest John .. https://vans.honestjohn.co.uk/van-revie ... addy-2015/

Basically they list the official mpg for a maxi as around 67.2 mpg but doubtless that is the number for the best - lightest base model - but yours is a Highline so it will be worse.

As the review notes "on average" real world users find they only achieve around 82% of official MPG figures.

Anyway 82% of 67.2mpg works out at 55.104 mpg. So if you are getting around 40mpg you are really down around 15 mpg.

That in turn could easily be down to a heap of minor things.

Even totally empty your Highline model will undoubtedly be dragging around more weight than a base model, and if you are running climate control AC most of the time then it will doubtless use more fuel than say a base model where the owner simply winds down a window if it gets too hot.

Fitting non-standard wheels/tyres should only really impact on things if they change either the effective rolling radius compared with the stock wheels/tyres or they alter the contact patch width - as obviously wider wheels will provide more grip but that must mean more drag likewise if you switch to stickier all season tyres.

If the effective rolling radius is enlarged then it would certainly impact on acceleration, so if they are still available it might be worth temporarily reinstating the stock tyres/wheels to see if your Maxi gets its mojo back.

If you prefer the aesthetics of bigger wheels, then hopefully your trip yesterday to have a professional remap on a rolling road set-up has helped. Those 2.0's are quite capable of delivering 170HP which should be more than enough to offset any tyre related drag - but you will inevitably use more fuel.

Then there are also several basic factors which might be worth checking.
Making sure your tyres are properly inflated - a few PSI down will steal mpg.
Dragging brakes or a bad wheel bearing can also gobble power and fuel.
A faulty thermostat could delay the engine warning up and impact engine performance
Supermarket fuel rarely delivers the best mpg.
Cruise control is not perfect especially if your daily drive has loads of hills. Hyper milers routinely outperform a microchip.

If you have the load space ply lined and kitted out with racking to hold a mass of tools and other dead weight inside the van that will impact your mpg.

Roof rails tend to be standard fit on most high-line models so they will inevitably add to aerodynamic drag, and obviously your mpg will get much worse if you are running around unnecessarily with roof bars or anything else attached on the roof.

Good luck

SnoWhite

Big wheels can have a massive impact - especially if they are heavier, but also, as the weight moves outwards towards the tyre, they take more energy to spin up, so accelerating is slower and consumption is higher unless you are at a constant speed all the time.

https://www.caranddriver.com/features/a ... els-tires/

It doesn't sound like your only issue though.

Monitor the coolant temp via VCDS, or the climate control secret menu if you have it. The gauge will read 90C from true 75C, and 75 still isn't optimal running temp - if it's anything below 90C on the gauge, it's drinking fuel at a higher rate than warm.

Thanks for the input guys. All taken on board and will check in the new year. Merry Xmas

NZDubNurd wrote: ↑Mon Dec 23, 2019 5:51 pm or the climate control secret menu if you have it.

Tell me more!

Try changing the maf and map sensors. Had the same issue couldnt really see any issues on vcds, changed the sensors felt like I had gained torque back and mpg figures increased.
Generally not good practice to throw parts at the van but if your frustrated and can find solutions.. could be worth the Gamble.