Volkswagen Passat CC 08 - Is this even right or what? | Technical matters | Back Room Forum

Tue 27 Jan 2015 17:03

Volkswagen Passat CC 08 - Is this even right or what? - Vandarius

Hi everyone,

I have a Passat CC 08, CR engine GT 140hpb diesel.

Somehow the consumption of the car just doesn't add up. When I start the car, it starts off with 8mpg, but it should be around 40mpg within the city. I have talked to many people who own cars with similar amenities and they say their average consumptions is 42-45 mpg. I think its just a huge-huge diffrence. However during driving it goes up to 27mgp or max 30mpg. But I tried to clear the data during driving and once it was cleared the consumption was at 47mpg.

To check the final value of the consumption I have filled up to the max and I drove a 100 miles and after I refuelled to max again. Then I calculated the fuel consumption and it was 28mpg for the city.

At first I was told it is bacuse of the DPF filters. Some "very clever" guy has offered me to remove it for £400. Obviously I said no. Then another guy said yeah the filter is clogged, we need to get it cleaned. It cost me £70 but everything has stayed the same.

I do not know why they keep saying that DPF filter is clogged because the sign has never ever appeared on the dash board.

Canthis really be the real consumption of the car? Or is there something wrong with it? Can somebody suggest something what could be the problem or I should just stop worrying.

Many thanks in advanave

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Tue 27 Jan 2015 17:13

Volkswagen Passat CC 08 - Is this even right or what? - gordonbennet

Take no notice of the OBC display, what's the consumption averaging out between fill ups, which is the only way to work it out accurately, and only then if the odometer is accurate.

Apparently remapping can have the side effect of making an even bigger pigs ear of the OBC readings, has the car been remapped.

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Tue 27 Jan 2015 19:56

Volkswagen Passat CC 08 - Is this even right or what? - Vandarius

Well like I said unfortunately the OBC display is right. I have calcuated the averages between fill ups and they were 27mpg.

I don't think the car has been remapped atleast not by me.

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Tue 27 Jan 2015 23:30

Volkswagen Passat CC 08 - Is this even right or what? - Peter.N.

A cold diesel engine driven in traffic can get down to those sort of figures but should improve considrably when warm and on the open road. To get a true reading, find a length of fairly flat motorway or dual carrigway and drive at a steady 60 mph having reset your trip computer, it should be doing about 60mpg

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Wed 28 Jan 2015 10:50

Volkswagen Passat CC 08 - Is this even right or what? - RobJP

I'll ask the question, mainly because nobody else has :

How are you calculating your fuel consumption (i.e the exact numbers you use)

Not meant to be insulting in any way, but I've seen some interesting uses of mathematics and calculators over the years, just want to check.

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Wed 28 Jan 2015 11:24

Volkswagen Passat CC 08 - Is this even right or what? - Vandarius

Basically I fill up full and when I've done for example 150km after I fill up again I double check hiw much went into the tank let's say 16L. From there I calculate (16L x 100km) /150km = 10.666L which is converted to UK mpg which gives the value of 27.

When I bought the car everything was fine even the consumption. But two weeks later the gas temperature sensor blew, I had it replaced and it is since then when the consumption is that bad.

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Wed 28 Jan 2015 12:25

Volkswagen Passat CC 08 - Is this even right or what? - Peter.N.

If it was that sudden I would conclude that the two are related.

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Wed 28 Jan 2015 14:33

Volkswagen Passat CC 08 - Is this even right or what? - dieselnut

I agree with Peter.

The fuel consumption suggests there is something seriously wrong.

It sound like the engine is continually trying to regen the DPF.

You need to get it to someone with good VW diagnostics, preferably an Independant, not a VW dealer.

Does the engine use any coolant?

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Wed 28 Jan 2015 15:28

Volkswagen Passat CC 08 - Is this even right or what? - Vandarius

I am now taking the car to an VW specialist to see what could be wrong. Today when I was driving I had 27mpg consumption, but I have cleared the computer data of the consumption immediatley it was 50 mpg.

Would the regen show on the dashboard?

I really don't know what could be the problem. Maybe the sensors?

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Wed 28 Jan 2015 16:10

Volkswagen Passat CC 08 - Is this even right or what? - Vandarius

What I really meant is basically on a given day when I start the car (cold engine) thats when the consumption is 27mpg from start to finish. But if I start the car and when it gets to warm up (the engine) and if then I clear the data then it becomes 37 mpg and it calculates it from there. I also assume maybe when I start car it just adds way too much fuel and that is when my consumption is stuck at 27mpg and I am not getting higher values.

I hope it makes sense.

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Wed 28 Jan 2015 16:12

Volkswagen Passat CC 08 - Is this even right or what? - madf

Sorry but when a car starts with a cold engine, mpg is pants...

When it is warn abd on a long run , mpg improves - a lot.

So your 27mpg could be starting cold and town running and your 50mpg is a warm engine on a flat open road.

I can see 100mpg from my Jazz down a hill... it's not real world over normal travel.

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Wed 28 Jan 2015 16:48

Volkswagen Passat CC 08 - Is this even right or what? - skidpan

Ignore the dash instant MPG display and the mpg display since start, they are only of any use for entertaining kids.

The only way to measure your mpg is over a decent mileage and several fill ups filling the tank at one garage and one pump. The gradient of the forcourt can make quite a difference to the amount of fuel you can get in.

My Leon will show 200 mpg every time I lift off, does not mean its doing 200 mpg.

My Leon will show 8mpg (or less) if I accelerate hard, does not mean its doing 8 mpg.

We had a Mondeo 2.0 TDCi 130 PS. On the wifes commute which was 8 miles each way at the time it would average about 35 mpg, less in winter. But give it a good long holiday run and 50 mpg was just about possible.

Edited by skidpan on 28/01/2015 at 16:50

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Wed 28 Jan 2015 19:10

Volkswagen Passat CC 08 - Is this even right or what? - dieselnut

" Would the regen show on the dashboard? "

You won't get any indication when the engine is doing a regen other than the cooling fan will run, & you probably won't be able to hear that unless you open the window while stationary.

I have a 2008 Passat similar to yours with the 2l CR engine & have never seen anything like 27mpg on the computer other than the first minute of running from cold.

I live on a 40mph limit road & by the time I have covered a mile the computer will be showing about 35mpg, after a further mile it will be on about 45mpg, but I live in a fairly quiet area with little congestion.

Earlier in the week I had to travel to central Manchester in the rush hour. A journey of 40 miles but it took 2 hours, so lots of congestion, a mixture of country A roads, motorway & town. The computer was showing 52mpg at the end of the journey & has proved to be fairly acurate when checked with brim to brim calculations.

The return journay, late morning & little congestion returned 58mpg. On the same journey in warm weather I have seen as much as 68mpg, but that was exceptional.

When you turn on the ignition does the glow plug light & DPF light illuminate for a second or two bfore you start the engine?

The DPF light will only illuminate while driving if the DPF starts to get over about 25% full. The glow plug light will start to flash at a higher % when the DPF is getting towards a critical capacity.

I would certainly get this sorted ASAP before the DPF sustains any damage.

Also check you engine oil level, it could be rising above the high mark if it's getting contaminated with unburnt diesel. If it gets too high that could also damage your engine.

If you join VWAUDIFORUM, there may be someone close to you who has the diagnostiv software & can interrogate the various controllers & find your problem for a few beer tokens.

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Thu 29 Jan 2015 19:50

Volkswagen Passat CC 08 - Is this even right or what? - Vandarius

Sorry but when a car starts with a cold engine, mpg is pants...

When it is warn abd on a long run , mpg improves - a lot.

So your 27mpg could be starting cold and town running and your 50mpg is a warm engine on a flat open road.

No worries but I know what to expect from a cold engine, but even when the engine is warming up or warmed up stays the same it just doesn't really make a difference.

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Thu 29 Jan 2015 19:53

Volkswagen Passat CC 08 - Is this even right or what? - Vandarius

Thanks everyone for the answers, I have found a relaible garage so booking a full diagnostics first on Monday to see.

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Fri 30 Jan 2015 18:16

Volkswagen Passat CC 08 - Is this even right or what? - dieselnut

Did you check if both the Glow Plug Coil & DPF symbol illuminate for a second when you turn on the ignition.

Otherwise the previous seller may have disconnected one or both to disguise a problem.

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Sat 31 Jan 2015 22:20

Volkswagen Passat CC 08 - Is this even right or what? - Vandarius

Did you check if both the Glow Plug Coil & DPF symbol illuminate for a second when you turn on the ignition.

Nope, I couldn't see anything at all. If they were, were they be glowing whit the other symbols such battery and the rest?

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Sun 1 Feb 2015 17:11

Volkswagen Passat CC 08 - Is this even right or what? - Vandarius

Just checked the symbols they are definitely there.

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Wed 4 Feb 2015 14:26

Volkswagen Passat CC 08 - Is this even right or what? - Vandarius

Thanks everyone for the answers.

Just a quick update. I took the car to a garage and they have done several tests to see what is wrong with it. Well NOTHING.

They didn't find any fault codes, and say that the DPF is clean. At the garage the technician said the higher consumption is down to the cars age. So this is it really.

Once again thanks everyone.

Vandarius

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Thu 5 Feb 2015 12:09

Volkswagen Passat CC 08 - Is this even right or what? - dieselnut

" They didn't find any fault codes "

Just because there are no codes logged doesn't mean there isn't a problem.

If one of the sensors is giving duff data back to the ECU, but still within the parameters of what the ECU expects, it may not throw up a code, but could well be causing the engine to run inefficiently.

Regarding the age of the car, that is total t*** t o s h. If the engine & running gear are in good condition, fuel consumption would be unaffected.

My Passat, 173k on the clock, the same year as yours & same engine will always return better than 60mpg on a motorway run ( 50 miles or more ) & kept to 70mph.

You need someone to look at the live data going to the ECU. Probably someone who does diagnostics only & knows what they are doing.

Edited by dieselnut on 05/02/2015 at 12:13

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