Because of the miles I cover in the Coupe (20,000+ per year) I have often considered buying a cheap diesel hack for commuting and business travelling - something like an Alfa 156 2.4.

However, yesterday, my mind was changed....

I had to do a trip down to Whiteley near Southampton to our head office. Round trip of 340 miles. When I go on my own, I use the Coupe and I get between 30 and 35 mpg, depening on how well (or not) I behave. It's certainly very easy to get low to mid-30s mpg

However, yesterday, I had to take three female collegues to the head office, so we hired a car - a 2011 diesel Insignia. None of the girls are petrolheads, so I was driving quite gently - no hard acceleration, no chucking it round corners (in fact two of them fell asleep on the way home, so it's obvious I was driving gently). On the motorway and DC, I cruised at around or above the NSL, but never above a speed that would get me pulled if I failed to spot an un-marked car. I filled up when I got home and calculated the mpg - 38. The car had done 43mpg average during its lifetime.

For me, the cost of petrol versus diesel doesn't come into the equation, as I only use V-Power, which is exactly the same price. However, if I was using normal 95RON, there would be an 8p per litre difference.

So - here's the results of a bit of Excel experiments

The cost of the journey in the Insignia was £60. The cost in my Coupe with V-Power on board would be £71 at 32mpg and £65.50 at 35mpg

The cost if I used 95RON would be £68 at 32mpg and £62 at 35mpg

At the speeds I was doing yesterday and the style of driving, I would definitely be somewhere around the 33-34mpg mark in the Coupe

The Insignia was SO easy to drive and very refined once above 40mph - if I had a 500+ mile trip, it would be a far more relaxing drive. However, it was hopelessly slow and numb and of course, it looked much the same as the other 50,000 Insignias that were also tooling up and down the motorways that day

So - used thoughtfully, the Coupe really isn't much worse than a (supposedly) economical modern oil-burner.

Go figure.....

The price difference between diesel and petrol is a bit ridiculous at the moment, and is certainly making me think about our 159 jtdm, which my wife uses mostly round town.

But 38mpg seems low on a run like that? Even in our 'old engined' 2007 159, I'd manage to get well into the 40's. And I'd expect a newer car/ engine to get higher than that. Are you sure you weren't coming home at licence threatening speeds??!

Which engine is in the Insignia? A lot of diesels would give better MPG than that, but don't forget you were 4 up and you're comparing the Coupe MPG with just you in it.

We never once hit three-figure speeds and it was mostly in the 80-85 range. On the way down it was never above 80.

The four-up comment is partly valid, but it makes no difference to the economy once you're up to speed.

I have to say I was surprised at the 38mpg return - I was expecting mid40s, especially as I was driving so gently

Maybe it was tired - it turned 30,000 miles on the journey, and I assume it's not been treated very well during its life as a hire car

Sounds like don't buy an insignia to me! Looks like it weighs 2 tonnes to me, that's why the Coop is economical because it's light. The GT is similar mass and the last tank was 46mpg. The 159 doesn't do this because.... it's too heavy, thanks SAAB!

That's well below par for what a diesel of the size should return for that kind of trip, what you need Nigel is a 2.4 tdi coupe!

I get a consistent 50-53 commuting in the 1.9 150 Bravo, though I tend to drive a little slower than Nigel and it's apparent that consumption gets worse as you speed up. Was still getting better than 40mpg cruising at 100 in Germany, though...

The thought had crossed my mind....

Just checked the weight of the Insignia - about 1600kg, so a bit lardy but not yet in BMW 5-series territory

Do GM still use the common Fiat/GM/Saab diesel or have they moved onto something different?

Edit - the Bravo is only 1300kg; that's four people different!

you wouldnt be too much better off in a 2.4 jtd Alfa, i seem to get around 40-42mpg, no matter how i drive, about 500 mile on a tank, but considering how expensive diesel is now if you work it out like that, diesel might be better off ever so slightly but driving in a coop would be my number 1 choice

What I really need is something that Leighton was thinking about - a dual-mapped ECU

At the flick of a switch, it would apply a "lean-burn" map, designed to run near-zero boost and little load. As well as this, we could probably rig up an electronic throttle stop and even an additional boost control to only allow modest throttle openings and only a tiny bit of positive boost.

I've certainly seen "hot switchable" dual eeproms before - one of our Scandinavian friends built one IIRC

My flea map is programmed for ron95 at 1 bar, Ron 97 at 1.2 bar. Two settings switchable via a Greddy Profec. Problem is, I've never run the low setting (nor used Ron95) ever since I got remapped. Takes out too much fun.

This one is still for sale at Solo Italia

http://www.ebay.co.uk/itm/Fiat-Coupe-1-9-8v-Turbo-Diesel/180828246954

Would be interesting to find out economy on it. That is where my interest ends

The whole point of a 20vt is the speed and acceleration. If it wasn't for this particular set-up I wouldn't even have one.

Interesting to see the conversion, I did wonder if the Alfa 2.4D would fit in place of the 20V engine. It would make for a very different drive and I probably wouldn't actually want to do it but the feasibility is interesting.

Seems a little poor for that engine...my Alfa 156 2.4 20v JTD returns around 42mpg around town and my driving is always a 50/50 split between makin the most of the 284lb/ft of torque (standard) and driving "comfortably"

My coupe however returns about 22mpg around town no matter how I drive...

On a long run though maxing out the tank I get 400 miles from the coupe and 700 from the Alfa and it costs the same to fill it up (super vs diesel)

The current model 520D is about 1625kg...

I took the wifes 1.3 Tdi Grande Punto up to Sheffield this weekend. I set the cruise control to 70mph max and drove in hyper miles mode. I had plenty of time so was in no rush and managed to obtain 68mpg for the run.

On the way back I didn't drive economically and returned just 50 Mpg!

I have noticed with this car that more speed (as little as 5mph), more people and erratic driving all significantly effect this little cars ability to return high mpg.

I have used the car on work runs, up and down the M11. If you stay at about 60mph and draft the trucks & coaches, it is possible to get the on board computer to show over 80mpg!

I would like manufacturers to publish the most fuel efficient motorway speeds in top gear for each car. We'd then know, if we were trying to be efficient, roughly what speed to aim around.

I reckon you had a duff one or got your Maths wrong.

My neighbour has a 2 litre CDTi with 100k on the clock. He does 40k+ miles a year and always gets mid to high 50s mpg. Just asked him to check the average mpg since he had it and its 55.9

Even my 10 year old Mundaneo 130bhp TDCi won't give me below 45mpg no matter how hard I drive it!

My Octavia vRS delivers around 60mpg at 60mph depending on traffic dropping to just over 50mpg at 70mph. Barely speed much, but had to get to the airport quickly recently and did a LOT more. Still averaged 42mpg.

Just to confirm that a Coupe can be (relatively) economical, I decided to take it easy today, because of the foul weather. Stuck to 65-70 (which is about as fast as the rest of the traffic was going)

Staffordshire to West Sussex and back - 361 miles, 42 litres = 39.0mpg

Quite pleased...

Nice!!

Headwork + 2lt = fuel consumption reduced!!

Ross

It was also much more relaxing than my normal pace - just about keeping up with the middle-lane traffic and of course, not having to keep eyes peeled for Plod

Bit boring though, especially when I had to decline an invitation to show up an M3

My old man has a 2.0 litre CDTi Insignia with 30K on the clock. It's the 160bhp model and I can confirm he is also lucky to hit an average of 40mpg. Ususally the trip computer shows around 38-39mpg. Nice enough car to drive tho and pulls well on the motorway (a bit sluggish around town). But yeah, the figures quoted by Nigel are probably pretty accurate.

J

A good friend of mine has a new Merc C220 diseasel with all the fancy stop-start gubbins

The "since-new" fuel consumption is 56mpg - very impressive, but it just goes to show how bad the Insignia was - confirmed by Jay above

Only if you were driving the 160bhp model though.

If you'd read my post on the Insignia above, you'd have seen my neighbour gets the same as the Merc