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O/T - diesel car - "modern" car why extra 30+percent fuel consumption?

Hi all

On this bright morning I thought to ask you here on r.c.m. if any of you know what makes the difference for a diesel car between very good fuel consumption and just good fuel consumption.

The punchline is - where is the extra 30+% fuel consumption going in a "modern" car?

UK / Europe factor - every car mentioned has manual ("stick-shift") transmission - five-speed or six-speed.

For nine years, I had a car which reached 20 years of age and went everywhere, every day, at 63MPG (Imperial 10pint gallon (4.536L); 50.4 miles per US Gallon; 22.2km-per-Litre). With plenty of power - delight to drive. Turbo spun-up and it surged forward no need for gear changes.

Even a vibrating rattly tiny Fiat supposed to do 70MPG (Imperial) did only 55MPG.

My current car mid-range (European style - probably very compact by US standards) is super luxurious, has a six-speed gearbox, goodly amount of power - no hills steep enough to keep speed below 70MPH when cleaning out the engine with sustained accelerator to floor - but "only" 48MPG (38.4miles per US gallon; 17km per Litre)

A few years ago I was told 60+MPG "is a thing of the past" "with new emission reg.s" (!!).

The 63MPG car, built in late 1990's, was turbo-diesel, fly-by-wire diesel injection, probably no filters or anything on the exhaust side of the engine. At 63MPG, it cannot have been throwing anything / much out of the exhaust part-combusted - else it wouldn't be doing 63MPG... It weighed 1~1/2tonnes - heavy for a smallish compact car. However, whatever that weight was, it seemed to be involved in something which nett left you advantaged. That was 1.9Litres - quite large by UK / Europe standards - where my more modern car is something like 1.6Litres capacity. It sounded like a tractor, for sure, when at idle.

That car, the 63MPG car, was Spanish built and badged from the Volkswagen stable. Someone told me it had the engine from the earlier VW Golf GTD (turbo diesel performance model). When that was no longer the new premium model.

So yes, if you could be happy with

a car which sounded like a tractor, you warmed it up slowly to be kind to the environment, didn't mind that the heaters only worked after about 3 miles of driving (if you aren't burning much fuel you are not producing much heat, plus you have a big heavy engine to warm up)

then you got a totally delightful car.

But that fuel consumption... 63MPG (Imperial) That is the possible.

Where is that extra 30+% fuel going in a "modern" car ???????

The 63MPG (Imperial) shows what is needed to do the job with a "straight diesel" car. So you can use that as a reference and ask - for a "modern" car, where is that extra 30+% of "un-accounted-for" fuel going ???????

I would be very very interested to know. I've had that question in my mind for since I found I couldn't like-for-like replace the wonderful VW-family car.

Regards, Rich Smith

Reply to
Richard Smith
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Rich,

Sounds like I might have the same engine in a slightly newer 1.9 TDI Passat and it's still going and hardly doing any mileage these days so I'm aiming to keep it going as long as possible, last model before DPF introduction. BTW a UK gallon is 8 pints it's the difference in UK and US pint sizes that makes the difference

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Reply to
David Billington

I forgot to mention in my other post but a mate recently raised the issue where he was getting noticeably poorer fuel consumption on current pump diesel than a few years ago. He runs a Nissan SUV, a FIAT camper van and for work a Ford Transit, all diesel and the vehicles haven't changed just he isn't getting the same distance out of a tank as he did a few years back. He mentioned the rumour? that cheap diesel from the supermarkets doesn’t get you as far and was wondering if the main brands where he buys his have changed the formulation somehow.

Reply to
David Billington

Thirty percent is pretty big. It would be hard to change diesel oil that much without causing engine problems. I wonder if the firmware has been reoptimized for low emission at any cost.

When VW was caught gaming the emissions tests, there was widespread talk of VW being forced to do exactly such a thing - it was to evade such a thing the prompted the cheating in the first place.

Joe Gwinn

Reply to
Joe Gwinn

The old car (tdi) cheated on the emissions - google "dieselgate" and emitted more tiny particles than allowed today. The new car is also slightly heavier (you said it was more luxurious - so more options and more sound deadening material) and with a 1.6 liter engine trying to do the same job the 1.9 did it is working harder - regardless of any weight increase.

Reply to
Clare Snyder

30+% is a lot, indeed. "Gaming the test" - "... has been reoptimized for low emission at any cost." (sic. - raising fuel consumption so putting out more CO2 is irrational?) I did wonder that - keep the performance and low fuel consumption in all normal driving.

There is a broader endemic issue here that any scheme which "locks everything down" (sic.) with a tight system of objective rules for an objective outcome will be gamed. Especially given the tunnel-vision of those swallowed-up in the rules-based-system, who can't see any distance that their "paradise they have imposed" is a tiny-distance illusion. That is a problem which at the moment is only increasing with "Standards", "Regulations" (a Law can set a general duty eg. "Safe, so far is as reasonably practicable" - Regulations can create fractal nonsense for which there is always a way out saying "we did every requirement and here is the filing cabinet proving it" when the reality is something grotesquely different)

Reply to
Richard Smith

The car from the late 1990's was first-principles technically excellent. It predated the highly presciptive emissions rules which might have irrationalities.

Still pondering - where does that extra 30+% of the fuel go?!

Reply to
Richard Smith

On Tue, 31 May 2022 08:17:45 +0100, Richard Smith snipped-for-privacy@void.com wrote as underneath :

I think possibly a fair chunk might be because comparative cars seem to be now much bigger than they were and a lot more comfortable, quieter etc, and presumably that is what the public wants? Quietness and comfort (and crash resilience) are weighty and "small" cars now to my eye are giants in comparison to comparative range models from earlier years, you might research the comparative weights and aero efficiency.

Reply to
Charlie+

The economical "63MPG" (Imperial gallon) car weighed 1~1/2tonnes according to the maker's plate - which if so would be quite heavy for a very modest sized car. ...

Reply to
Richard Smith

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