New car petrol consumption - Ian Smallwood
Some weeks ago, I wrote expressing disappointment that my new car did far fewer mpg than I had been led to believe from the published figures.

All the backroom responses, either implicitly or explicitly, suggested that I should not be surprised.

Now with 2500 miles on the clock, economy is pretty close to the published figures - I reckon it is averaging a good 4 mpg more than it did when new.

Why didn't anyone tell me that would happen? Can I expect further improvement and, if so, up to what mileage? Is an improvement of 4 mpg between new-car-economy and run-in-car-economy a record?

(I'm well versed in the methods of monitoring economy, so I don't want to start that thread again.)
Re: New car petrol consumption - Alvin Booth
Ian,
I keep a close record of fuel consumption on my vehicles saved on to my computer and the ambient temperature means a difference of 3 to 4 mpg between summer and winter. And it has been a lot warmer just lately.........

Alvin
Re: New car petrol consumption - John Slaughter
Ian

We went down this road recently, and your data confirm what many of us believe - best economy is obtained in summer.


regards

John
Re: New car petrol consumption - Tom Shaw
Keeping detailed records of fuel expenditure and milage for tax records, I have found that with diesels optimum fuel economy is achieved at around 20,000 miles. Probably be a lot sooner for petrol engines, but the engine has to be well run in before it will perform at it's best. I would also agree with Alvin that the warmer weather makes a noticeable difference.
Re: New car petrol consumption - David Lacey
I always take manufacturer fuel consumption figures with a pinch of salt! They seem over-optimistic and rarely achievable in real-world motoring. It is a battle I have with many customers over the year! Our adapted gallon fuel can with inlet and return unions has settled many a fuel consumption dispute in the past! Just fill it with a gallon of fuel and drive normally and see how far we can get!
I would agree that a car will not return optimum economy until it has covered at least 15-20K to allow the engine to loosen up and the management system to learn the driving style etc.
Ambient temperature as Alvin rightly states plays a major part in fuel economy, many people overlook this.
Incidentally Ian, what car do you drive?
Regards
David L
Re: New car petrol consumption - Ian Smallwood
Its a new Laguna 2, with a 1.6 engine that I expected to be relatively underpowered, but then I've a very gentle foot and came out of 3 years using a 2 litre automatic Scorpio, so I haven't lost much in the way of performance!

2 previous 2 litre Renault 25's preceded the Scorpio and I've had fun with the trip computer in all of four of them.
Re: New car petrol consumption - Mike
Some comments, following this thread:
- I had a June 97 2.0LX Mondeo (facelift model). I reckon it took 10,000 miles to reach its prime in terms of fuel consumption, flexibility etc, but from then on I regularly got 34mpg in the winter, 38mpg in the summer. AIrcon made no difference to economy but flexibility suffered;
- I currently have a Saab 9-3 2.2Tid (diesel). I get almost exactly the manufacturers combined figure of 45.6 mpg at a minimum, usually more. Doesn't vary so much between summer/winter (probably c.2mpg) Aircon makes no perceptible difference to consumption or power (good job really, there is nothing to indicate that the aircon is on & I leave it on by mistake for a few days sometimes!);
- my old Saab 9000 does 31mpg winter, 35mpg summer (no aircon other than windows);
- a recent report in the Daily Telegraph said that scientists were surprised to discover that brisk acceleration through the gears to cruising speed (whether 30mph or 70mph) was better for fuel consumption than slower, more gradual acceleration. I tried it, I reckon it works on my Saab 9-3;
- mountains kill fuel consumption on diesel due to the narrow power bands (see my earlier contribution under "Diesel torque).

Hope this is of interest!
Re: New car petrol consumption - John Slaughter
Mike

Interesting comment about diesel economy.

I had a 406HDI on rent for a number of days recently. Long runs every day and I brimmed the tank every night. Several days were mostly motorway and it did close to 50miles/gall. A few days were A & B roads, including a few hilly miles, where I had to use the revs (I think from the performance it was the 90bhp version). Result - it barely did 40. Now, neither of these are bad, but my old 2l petrol Vectra would do 40 miles/gall on a long run with no great variation between the road types. Confirms the theory that fuel governed diesels have the main economy benefit over throttle governed petrols only when they are not driven hard.

regards

john
Re: New car petrol consumption - John Kenyon
John Slaughter wrote:
>

> between the road types. Confirms the theory that fuel
> governed diesels have the main economy benefit over throttle
> governed petrols only when they are not driven hard.
>

But diesels don't have a throttle, they have a speed control input,
either into the distributor pump, or an ECU which controls fuelling.
The closest you get to a throttle on a diesel is the choke device
fitted on some engines.

/John
Re: New car petrol consumption - John Slaughter
John

Er, yes, that's pretty much what I was saying!

Regards

John
Re: New car petrol consumption - Mike
I think what we're all saying is that petrol cars will probably have more consistent consumption, but generally worse than diesels, whereas driving style/conditions will affect a diesel more, but overall they are likely to have better consumption.

I use a cruise control on my Saab & I think that definitely helps on motorways.
Re: New car petrol consumption - John Kenyon
John Slaughter wrote:
>
> John
>
> Er, yes, that's pretty much what I was saying!
>

D'oh!

Memo to self - read original post before posting!
Re: New car petrol consumption - stuart bruce
Its always interesting when people are making observations about fuel consumption on a petrol engine there is generally the suffix "on a long run"

But you rarely get the mention of the real life situation which is, for most of us, a complete mix of urban, extra urban low and high speed, motorway, which actually makes the real comparison of fuel consumption open to so many experimental erors that you have to have quite a significant +/- allowance, which Guy Lacey indicated in another thread.

As I have mentioned elsewhere I have driven oil burners atmo & turbo for some time and I too find the diesel economy advantage reduced to nowt when you are giving it some welly, but the proportion of time when you are on part or low throttle situations, which lets face it is most of the time on today's roads, means that in real life situations diesel is better.

Some months back drove a Volvo S80 2.4 (5 cyls?) The area was flat and the roads quiet, the only detrimental effect to consumption was that it was on knobblies and spikes, hence it was also pretty cold weather. Out of town the fuel consumption, as indicated by the computer, assuming reasonable accuracy, would have put my normal GM Ecotec 2.0DTi to shame, plus it was amazingly flexible, plus it went like the bars. But as soon as it got round town and into traffic it was down in low 20s and sometimes below. With the proportion of traffic work we get in the UK it would have made the fuel costs unsustainable.

In all my previous cars the band within which the consumption figures fell gradually rose gently throughout the life of the vehicle, ignoring seasonal variations, with the exception of the current Ecotec, which as someone indicated earlier seems to have peaked at about 20k. Very strange.

PS As David Woollard keeps telling us, number of posts just into double figures and we have got it round to diesel vs petrol, sorry I could not get in a proper reference to BXs and the excellent XUD engine David.
Topic bending. - David Woollard
Stuart wrote......."As David Woollard keeps telling us, number of posts just into double figures and we have got it round to diesel vs petrol, sorry I could not get in a proper reference to BXs and the excellent XUD engine David."

But you did Stuart. Just the brief mention is enough to qualify the thread as complete. Now I can concentrate on topic bending elsewhere.

David
 

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