Vauxhall Astra J 1.7 cdti ecoflex - Dreadful fuel economy

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Wed 3 Jun 2015 18:22
Vauxhall Astra J 1.7 cdti ecoflex - Dreadful fuel economy - mikejharvey

I have recently bought a 62 plate Astra 1.7 cdti ecoflex (110) Sports Tourer to replace my aging 170,000 mile 1.3 cdti estate. On a 630 mile run to my holiday shack in Brittany, the old 1.3 regularly did 56+ mpg (never quite got 60 though sometimes tantalisingly close!) I foolishly thought the newer 1.7 would do about the same, but last week it did just 46mpg there and back. Thats about 20% worse!

It has the right Michelin energy tyres inflated to higher pressures, driving speed just the same , ie 130kph (80mph) most of the way there once in France, and motorway 210 miles to Dover. The only difference is I used cruise control quite a lot, and the old 1.3 did fail to maintain 130kph up some of the steeper inclines.

I have phoned local Vauxhall dealer to see if there is a software update, and they say no.

Have any of you any ideas to improve things? I had hoped to keep the car for another 150,000 miles, and at this rate it will be too dear!

I had thought of chipping, but do not want performance, just economy, and no rise in insurance costs.

I would be most grateful. Regards, Mike

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Thu 4 Jun 2015 07:28
Vauxhall Astra J 1.7 cdti ecoflex - Dreadful fuel economy - madf

46mpg at 80mpg sounds about right. Try 65mph if you are worried about fuel consumption.

Air resistance is proportional to speed SQUARED...

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Thu 4 Jun 2015 08:47
Vauxhall Astra J 1.7 cdti ecoflex - Dreadful fuel economy - mikejharvey

Thanks for your thoughts. I agree completely about dropping the speed, but my point was that the old 1.3 did 56 mpg + under the same conditions, and I had expected a newer car with lower CO2 emissions to more or less match it. I am effectively moving the same mass over the same distance with the same wind resistance, but using 20% more energy. Why? I suspect the new Astra is a little bigger frontal area, and the tyres are wider giving a higher co-efficient of drag, but 20% worse. It's terrible!

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Thu 4 Jun 2015 09:49
Vauxhall Astra J 1.7 cdti ecoflex - Dreadful fuel economy - skidpan

The first mistake you made is

I had expected a newer car with lower CO2 emissions to more or less match it

Manufacturers (all of them) have become much cleverer at getting rediculous figures in the official tests so to put it simply you cannot compare old with new.

Your old car was a 1.3, your new car is a 1.7. Providing you old car was not a gutless wonder that needed thrashing all the time its highly unlikely one with a bigger engine will match it. For starters the bigger engine will most probably be heavier and defineitely have more internal friction.

Wider tyres use extra fuel not only due to friction but also because of wind resistance.

Look at the figures on this site for the 2 cars. The old 1.3 has a figure of 52.6 mpg, the newer 1.7 110ps a figure of about 46 mpg.

Does that look familiar.

Slow down and save money, its the only way if mpg worries you and in truth unless the roads are totally empty (which they never are) trying to do 80 mph instead of really doing 70 mph saves very little on journey times.

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Thu 4 Jun 2015 10:02
Vauxhall Astra J 1.7 cdti ecoflex - Dreadful fuel economy - RobJP

Slow down and save money, its the only way if mpg worries you and in truth unless the roads are totally empty (which they never are) trying to do 80 mph instead of really doing 70 mph saves very little on journey times.

An interesting side point : many years ago a girlfried (we were in uni together) who's home was near Chorley in Lancashire had a minor bump while driving. Called me (in North Wales), all tearful, panicky, etc. So I jump in the car. Normally, that journey took me 60-65 minutes, driving at 75-80. This time, I drove considerably faster (regularly topping 100). It took me 58 minutes.

At that point I decided that the added stress of 'pushing it' just wasn't worth it. Driving within the limit you aren't constantly worrying about police cars/cameras, you can relax so much more because the speed differentials with other traffic are so much less, and basically enjoy the journey.

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Thu 4 Jun 2015 10:31
Vauxhall Astra J 1.7 cdti ecoflex - Dreadful fuel economy - Peter.N.

I used to cover about 30k miles a year when I was working, I was a bit of a boy racer when younger but at that sort of mileage it tends to be tiring especially as you get older so for many years I have been happy to sit a 60 mph in the slow lane, you get less stressed and tired, the journey dosen't take that much longer, but the ultimate benifit is to your fuel consumption.

We have just returned from a 2000 mile trip to and around the north of Scotland with an indicated average fuel consumption of 64.3 mpg, actual calculated figure nearer 58 mpg, still not bad for a quite heavily loaded 406 Hdi estate.

For 15 years I ran Citroen XM estates with the 2.1 IDI engine and managed over 50 mpg on the same Scottish trip.

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Thu 4 Jun 2015 10:27
Vauxhall Astra J 1.7 cdti ecoflex - Dreadful fuel economy - mikejharvey

I did look at Real Fuel consumption figures on Honest John site prior to buying the car, and it turned out to be bang on!

So, if the manufacturers are clever at mapping the cars to give the 'unreal' government fuel consumption figures. I need someone to re-map it back to the real world and give me better economy!

I remember when I sold Vauxhalls back in the 80's, the Calibra had a co-efficient of drag of 0.29 for the basic model,(claimed to be the lowest of any production car) and 0.3 for the sportier 16v, the difference being the wider frontal area of the tyres.

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Thu 4 Jun 2015 12:42
Vauxhall Astra J 1.7 cdti ecoflex - Dreadful fuel economy - daveyjp

A 110 bhp diesel doing the same mpg as my 90ish bhp similarly sized petrol. With those figures that diesel looks to be a bad buy.

A friend has a Skoda Superb estate greenline and he has just done a trip from Wiltshire to Suffolk. He photographed the on board computer as he was amazed that it was showing 74.3mpg for the trip. Actual was almost 70mpg.

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Thu 4 Jun 2015 13:07
Vauxhall Astra J 1.7 cdti ecoflex - Dreadful fuel economy - RobJP

A 110 bhp diesel doing the same mpg as my 90ish bhp similarly sized petrol. With those figures that diesel looks to be a bad buy.

A friend has a Skoda Superb estate greenline and he has just done a trip from Wiltshire to Suffolk. He photographed the on board computer as he was amazed that it was showing 74.3mpg for the trip. Actual was almost 70mpg.

But I'll bet your friend wasn't doing 80mph, unlike the OP.

I don't think the figures the OP has got are too bad. My BMW estate will average 55 mpg on a long gentle run up to Scotland with the cruise set at 73, however move it to 78 and it drops to more like 50.

The other thing that the OP doesn't tell us is if those are the trip computer figures or the REAL figures. If trip computer, the old car could asily have been 5-10% out, and the new car being dead accurate. Meaning there is almost no difference.

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Thu 4 Jun 2015 14:42
Vauxhall Astra J 1.7 cdti ecoflex - Dreadful fuel economy - skidpan

So, if the manufacturers are clever at mapping the cars to give the 'unreal' government fuel consumption figures. I need someone to re-map it back to the real world and give me better economy!

Do you honestly think that a man in a shed with a laptop can do a better job than a multination corporation like GM with untold development monies. If he was so good he would not be in a shed selling his supposed "economy or performance maps" on e-bay, he would be earning a huge salery working for one of the major manufacturers and being hailed for saving the planet.

Ever heard anyone say if it looks too good to be true it probably is.

Reality check required here.

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Thu 4 Jun 2015 21:24
Vauxhall Astra J 1.7 cdti ecoflex - Dreadful fuel economy - Railroad.
I find that between 60-65mph is the speed that returns the best balance between fuel economy and drivability. Any faster and the mpg begins to suffer. Much slower and I feel like I'm never going to get there. At this speed my Octavia 1.6 TDi will return an average of over 60mpg according to the trip computer.
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Thu 4 Jun 2015 22:47
Vauxhall Astra J 1.7 cdti ecoflex - Dreadful fuel economy - mikejharvey

Thanks for all your opinions and responses. Much appreciated, though not always what I wanted to hear!

The figures I quote are accurate brim to brim figures, but relying on the indicated mileage, and calculations at 1 gallon = 4.54 litres. No trip computer on either car.

If the ferry and traffic in the UK is OK, I can just about do it door to door in 12 hours, and reducing the speed to 70 will add a good hour to the journey! I sometimes have to do that when it's wet and it is so slow!

Cheers.

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