New Passat :: Drop in Fuel Economy

[nheather]

I have a new style Passat saloon (2.0 TDi Sport 140PS) and since the first service 2 weeks ago I have noticed a considerable drop in fuel economy.

For the first weeks after the service, journies were just my normal commute to work and whilst I noticed a fall from 47mpg to 43mpg I was too concerned because the journey can be variable depending on traffic.

But over the last few days I have done two long and clear motorways journies.

Before the service I would have got 55mpg easily but now I'm struggling to get 47mpg for the same driving style.

I contacted the VW Service Centre - initially they refuted that nothing they did could possibly change the fuel econonmy. I pointed out the service report which showed that they did a Software Update (23C4). His story then changed to "that would just maker it better if it changed it at all". I pointed out that regardless my fuel economy had fallen - the response was to try another couple of tanks and if it is the same he will arrange to have it looked out (though I suspect it will be no fault found).

So my questions here are

(a) Anyone in a similar situation noticed a drop in fuel economy?
(b) Is it possible to find out what a Software Update does?
(c) Is it possible to have the old software version restored?

Thanks for the help,

Nigel

[wardiebhoy]

nigel,
dont really know mate but the way everyone keeps talking about a "vag-com" these are diagnostic tools that hook up too your car , via a pc then basically tell you everything thats wrong with them, theres some other threads in here somewhere if you look that will help you more , hopefully this helps .. ( a little :o )

[snapdragon]

Could it be the winter diesel we are now on? (lower calorific value)

[nheather]

@snapdragon

That could make sense.

Didn't realise they did this for UK.

Cheers,

Nigel

[snapdragon]

Yes, by law it has to be winter diesel after Oct 31st, I think for a month before that date it is called 'intermediate' so can be any mixture of summer and winter diesel. I think it changes back March-April.

[Roy]

My experience is the opposite of yours, prior to the update, on the motorway (steady 75-80 run over 70 miles) run it would settle at about 51mpg average. Since the software update (also 23C4) it now shows 56mpg. The effect hasn't registered on the long term mpg memeory yet which is still showing 48mpg. Before the update the fuel computer was quite accurate, within a few percent (verified over several fillups). I'll monitor it again now the software's updated.

The car went in because a 'deadspot' developed around 1900rpm, this was becoming very noticable in 6th gear whe re-applying light throttle following a period of 'coasting' with no throttle. The update cured this completely.

Roy

[jamie]

Did you ever resolve this problem? I have a similar issue. Fuel economy also around 43-47 mpg when it was previously doing 51+ with same driving.

Difference was noted after I took it to a local garage to get cambelt replaced and full service completed.

Jamie

[AndrewT]

I've also noticed an increase in fuel consumption - my car has the DSG gearbox. Over 20,000 miles I have averaged qround 43 mpg - about right - over the past few weeks it is down to between 35 & 37!

The car is booked in for a service next week. I'll let you know what they say.

A friend of mine has an A4 Tdi 140 manual - in his first 15,000 miles he has averaged 53 mpg

[jamie]

actually searched the forum and found a posting by 'glynnd' titled 'fuel economy' which he explains dropped after his cambelt was changed (same as mine). I am going to speak to my garage with the similar question.

[alicycling]

I've got a similar thread at the moment. I had my drive belt changed and the fuel effciency has dropped from about 55mpg to 50 mpg. I had it done at a local garage so I don't think they'll be able to diagnose it. I'm now thinking of taking it to a VW dealer to get the 'official' line but am hesitant as I'm sure it will cost over £100 just to hook it to a diagnostic machine.

Cheers and I hope you get a solution.

[Baron_Samedi]

Anecdotal I know, but....

When my Passat went into the dealer for its first service it came back:

a) with reduced economy

and

b) a slight hesitation on light acceleration

I ignored it until....

Driving back from an airport, the car suddenly lost power and created one hell of a plume of grey smoke out the exhaust for a few minutes. Car was almost undriveable but got me home.

Gave it back to the dealer to be informed later in the day that the turbo boost hose had become detached.

Subsequently, the economy returned and the hesitation disappeared :D

So... the moral of this story is that the technicians aren't too careful when servicing and dislodged the pipe causing a slight problem that became a major one.... get them to check all the pipework!