Motorway fuel economy - Ian Smallwood
I have a changed cars from a 2L car engine to a 1.6L hoping for greater economy. The 1.6L car is much more economical in "general driving" but about 5 mpg worse (35mpg against 40 mpg) on a steady 70-75 mph long run on the motorway. Am I going to have to stick to 55mph on the motorway, or is there something wrong with my new car? (Published figures Urban cold 28.5 mpg, Extra-urban 49.5 mpg, Combined 39.2 mpg)
Re: Motorway fuel economy - Roger Jones
This looks like a familiar example of some of the fallacies surrounding fuel economy and environmental benefits. That smaller cars consume less and pollute less ain't necessarily so. I find no surprise in a 2-litre car being more economical at motorway speeds than a 1.6-litre car, given the likely differences in gearing, engine design, etc. If they aren't variants of the same model, then there may be significant differences in aerodynamic behaviour too.

I drive a large car with a 3.2 engine (M-B 320 Coupé automatic); my partner drives a much smaller car with a 2.8 engine (VW Golf VR6 manual). Overall, I get more MPG than she does, because of the greater average trip length and the different style of driving. Even on comparable trips in the Golf I get more MPG through smoother driving and less use of the gearbox.

And just to round this off, I bet that a poorly maintained 1.1-litre car will be more environmentally damaging than a well maintained 3-litre car, even if it does consume less fuel.
Re: Motorway fuel economy - Tom
This really does not surprise me either. Just got a 1.2 litre car previously had a 1.05 Polo. On the motorway at 80-85 can get around 36-40 mpg out of the 1.2 at best in the Polo 30 mpg. The only thing is around town this is swapped. Regularly get 26-30 out of the 1.2 and usually got 34 mpg out of 1.0.

I have a theory that a larger car cruising is likely to be working at lower revs than say the 1.6 and it probably delivers its peak torque at lower revs which must be more efficient.

Having said that recently borrowed my mother's "Granny Car" 93 Rover 214 sli and drove from London to Leeds at 95-100 (v. late at night don't tell Tony Blair!!!) and got 42 mpg I was amazed especially as 3 weeks later the cylinder head gasket went and it needed a new head as it was warped and porous!

Re: Motorway fuel economy - John Slaughter
Exactly - most 2.0litres are running nicely around peak torque on the motorway, so economy is good. Also you're not always booting them so hard to regain cruising speed.

Just to confirm what you thought, most people I know who have run 2.0 l Vectras get up to 40mpg on motorway runs, at least as good as your 1.2

Re: Motorway fuel economy - Gwyn Parry
Yes - John, I can confirm the Vectra's fuel economy....does 35mpg day in day out come hell or high water, regardless of loading - even when driven with a feather right foot in the petrol wars still turned 35 mpg !!!! Get it on the motorway and will do 40 to 45 mpg at a steady 85mph......... down to a lcak of gear changes I suppose. One of the few redeeming features of the Vectra is its motorway cruising.. fast smooth and frugal..makes me wonder why I hate it so.
Re: Motorway fuel economy - John Slaughter

Yes, the Vectra won Fleet Car awards very regularly, and it's probably because it suits high mileage motorway driving, and is very economical. In my experience they rarely go wrong - my car was always very reliable, having only a couple of minor faults in nearly 80k miles, and it was still tight and rattle free. I don't recall any colleagues having any reliability problems, despite doing up to 40k/year. I was happy to buy it at 67k when I left my last job. I've always wondered about the slating from the press, as fleet managers seem to like them so much. The only downside is the handling - it's not as sharp as some rivals.

I've just traded mine in and got a '99 BMW 323 Coupe. Faster and handles better than the Vectra, but I bet it won't be as cheap to run. Still, got to have some fun!



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