This may be normal, or an isolated one off but I am confused.

I do a big mileage commute, same route, everyday albeit at differing times of day due to shifts.

Finished my first tank of fuel this morning. Topped up with 1/8th of a tank remaining, having done 600 miles. Average consumption on the maxidot was showing as 67.2mpg, taking the tank to one click full suggested 62.7mpg - so a bit off but ok, that's fine.

Got in the car to drive home and immediately noticed the consumption on the instant consumption readout was significantly lower than usual - indicating 50-60 mpg where just this morning or yesterday on the motorway I rarely saw less than 60 and often it hovered in the 70's. Indeed, the opposite run this morning the maxidot recorded the average as 82.1mpg. Last night going same route average was indicated 77.4mpg.

Tonight, same journey, same speed, equivalent traffic I get 64.4mpg.

So what gas happened? Does the maxidot learn tank by tank and it's adjusting? I just can't see how the car can suddenly drop 13mpg (20%!!!!!) if not...

So it's showing worse consumption on your way home? Could be there's a very slight climb this resulting in higher fuel consumption.

Road surface could also be playing a part.

Erm yes, but same trip home has been 72mpg, 77mpg then 64mpg - suddenly a drop of 13mpg from one day to the next.

Pretty sure they didn't change the road surface in 24 hours.

Will be interesting to see what happens this afternoon on the way to work

After fill-up you've got an extra 40kg+ onboard to start with which will make a difference. Just keep tabs on how much it's averaging tank after tank, Fuelly is good for this. And then you can keep notes and see what might be affecting mpg to help you eek out extra mileage if that's your bag. Probably not a lot to learn, or indeed be worried about, from your first tank of fuel! Needs time to bed in and settle.

Oh, and make sure you give it a hefty prod at least once a drive. This will affect your economy, but my 1.2TSi has had some stick (within the recommended rev limits) and hasn't used a drop of oil in 1k miles and is returning 48mpg every day on the work commute. Good bedding in will help economy in the long run

I'd largely ignore the maxidot to be honest, work it out the old fashioned way and report back!

Ok, I get the extra weight but still, a 20% drop in economy? I need to go on a diet!!!!!

Hi Whitelighter,

Although it's natural to do so, and with all due respect, I wouldn't be worrying about fuel consumption at the moment. You need to be concentrating on bedding in your engine first. Otherwise your engine will never attain good power output and consistent fuel economy. Fuel economy driving runs are very bad for new engines, particularly diesel engines, and will result in your engine not being 'run in'. Diesel engines are harder to run in than petrol car engines, and in this new breed of diesel engine this seems to affect them unduly if it's not done properly. This is in part due to the fuel itself which unlike petrol which is a solvent and washes a certain amount of oil away from the pistons and rings, diesel fuel is actually a very good lubricant and further lubes the pistons and rings along with the engines normal oil lubrication. Getting the much needed and vital metal to metal contact between pistons, rings and cylinder bores is therefore much much harder and requires the power to be used often with due regard to the running in instructions in the manual. Avoid constant speed running with a set throttle position during running in, vary it a lot and the load on the engine too. Gradually allow the revs to build more as you cover more miles. You want the piston rings to be pushed out hard to the cylinder bores to make the proper metal to metal contact when the engine is hot, not when it is cold of course. That would cause damage if it's cold. The 1.6cr engine is very tight when new, producing around 8-10% less power during the first 1000 miles of life due to the extra friction it has to over come. This also means that any extra load on the engine (such as when you have just filled up as Miffy says) or if going into a headwind on the way home, climbing gradients etc etc, will all disproportionately affect fuel economy during running in and actually during the first 2-3k of miles travelled.

You will be amazed at just how much your new engine improves as the miles go on it, but not if you don't run it in properly so I would forget worrying about the fuel consumption at the moment and get your foot down. You cannot hurt a diesel engine during running in by giving it some beans, but you can by not doing so! Good luck with the car, it sounds brilliant so far and what you are experiencing is completely normal regarding consumption. Many people experience just the same with their new diesel.

Cheers estate man,

I asked the dealer about running in but they said drive normally.

I do try to drive it harder off the motorway, but a 160 mile daily commute on the m25 does make it a bit hard.

The good news is 3000 miles is only a month away

Nice one! The ecu will have stopped learning too by then and things should start to settle down gradually. The bedding in process will continue for another 6-7k miles. Surprising isn't it! Have fun with it and don't worry about anything. It will all be fine.

What was the wind speed and direction?

Tony

You must be driving Miss Daisy to be getting 77mpg :yes:

Hmm, wind was maybe 15-20mph on the nose ish (well more in front than behind)

I used to fixate on the immediate economy.......After many miles I realise this is a complete folly.Not to mention the risk of piling in to the back of another car while studying the readout more often than is healthy.....

You want an accurate trend of your mpg then its the trusty calculator, pen and paper every fill up.

Slightly hypocritical of me considering mine is at the repairers undergoing £4000 of front end damage repair (very large deer at night). No I wasnt looking at anything other than the road, oh and my life as it flashed past me on impact)

Edited 7 October, 201114 yr by raisbeck

I don't fixate on the immediate, I look at the average after the journey (80 miles ish)

I used to fixate on the immediate economy.......After many miles I realise this is a complete folly.Not to mention the risk of piling in to the back of another car while studying the readout more often than is healthy.....

You want an accurate trend of your mpg then its the trusty calculator, pen and paper every fill up.

Slightly hypocritical of me considering mine is at the repairers undergoing £4000 of front end damage repair (very large deer at night). No I wasnt looking at anything other than the road, oh and my life as it flashed past me on impact)

Lucky for you it wasn't the antlers "the last thing going through your mind"