I’ve just stepped out of my 1995 Peugeot 405 SRDT
turbo diesel sedan, having driven it 800 kilometres in two days, making a
holiday trip loaded with a bootful of luggage and my wife and 3-year-old (no,
they weren’t in the boot).
When I arrived home, I saw sitting the driveway my
2001 Honda Insight hybrid and my wife’s 1998 Toyota Prius hybrid – the latter’s
the one with the defective high voltage battery. As a motoring journalist, I
have also driven current model Volkswagen, Peugeot, Audi and Hyundai diesels,
the current model Prius (in fact I drove that car across half of Australia and
back) and the Honda Civic Hybrid. So, unlike most who seem to write on this
topic, I have personal ownership experience of hybrid and diesel cars as well as
test car experience.
So, which automotive engineering approach is best
– conventional petrol, hybrid petrol/electric or diesel? Listening to some
people you’d figure, with equal strength of belief, that:
-
Hybrids are just wanky cars for those who like to
appear green
-
Diesels are slow, noisy and polluting
-
Hybrids are for city and diesels are for
country
-
Conventional petrol engine cars can do all that
either diesels or hybrids can do – and at a much lower cost
In fact, I think every one of these statements is
rubbish. Why? Let’s take a look at the misconceptions.
If the quality of the car was symptomatic of the
quality of the owner, only dickheads would ever have driven rotaries, all WRX
owners can’t drive and late model Monaro drivers are all in their sixties and
are driving the cushy thing they deserve.
Stereotyping owners is stupid
automotive engineering analysis.
Maybe people buy the Prius because they want to
look green – but who cares? Maybe government departments buy the Prius because
they want to be seen to be doing something environmentally friendly – but that
has nothing to do with the green credentials of the car itself.
The bottom line is that on the
Australian
Government’s Green Vehicle Guide,
the top performer in terms of fuel economy and emissions is the Toyota Prius.
So the most impartial guide to cars in Australia
lists the Prius as the best 'green' new car you can buy. Full stop.
Diesels don’t need to be slow – the European
manufacturers (eg Audi and BMW) are now selling in Australia very powerful turbo
diesels, ones no one would suggest are slow. However, if you develop a lot of
power in a heavy car, that performance is paid for at the pump - irrespective of
whether that pump flows petrol or diesel.
So it’s true to say that the best performers in
fuel economy (and so, consequently, in greenhouse gas emissions) are not
fast cars. That’s exactly as you’d expect, is the same as it’s always been, and
is the same as you’d expect it to always be! (Maybe in the future, short-range
hi-po electric cars excepted.)
Noise? Diesels certainly have a characteristic
clatter audible from outside the vehicle – for a roadside pedestrian, picking a
diesel from a petrol engine is pretty easy. But inside the car, noise levels are
now much the same for petrol and diesel. The note may be a little different, but
the sound pressure level is in the same ballpark.
But it is in pollution where the statement holds
the greatest truth. Diesels, intrinsically, have higher polluting levels of
oxides of nitrogen and particulates. The latest diesels are vastly better in
these regards, but they still struggle against the quality of petrol engine
emissions, let alone hybrid emissions. Band-aids such as the widely-billed
Mercedes BlueTec treatments are all well and good, but the emissions road for
diesels is still steeply uphill.
The idea that hybrids are for the city and diesels
for the country seems to have gathered currency, even amongst those professional
engineers and scientists who should know better. Why should they know better?
Well, it depends on the vehicles in which the respective drivelines are placed!
In a lightweight, small and aerodynamic car, a
hybrid can get excellent open-road economy. In a large, powerful and heavy car,
a diesel can get relatively poor open road economy. What people might believe
they are saying is that, in the same vehicle and with the same power, a
diesel will give better country road results than a hybrid. That may in fact be
the case... except we don’t currently have cars that fit those criteria.
When AutoSpeed drove a current model Toyota Prius
from the Gold Coast to Adelaide and back we gained 5.3 litres/100km for most of
the trip. When we did a long country drive in a similar size Peugeot 406 diesel
turbo (a car that gets better economy than the current larger and heavier 407
model) we got a poorer 5.9 litres/100km.
What people really mean is that in
city conditions a hybrid will simply kill a diesel for economy,
whereas on the open road, it will be a closer match. That’s a very different
statement to the one highlighted in bold above.
People love making comparisons of Prius fuel
economy to the economy of the Ford Festiva, Daihatsu Handi Van, Honda Jazz and a
host of other old and new small economy cars. Trouble is, the Prius is in a
completely different class in terms of interior space, performance, safety,
features and comfort. Take each of these criteria into account, then make a
valid comparison to another car, and the outstanding fuel economy results of the
Prius become clear.
I’ve even seen people say the Prius is vastly too
expensive – but AFAIK, when it was released in I-Tech form, it was the only car
in its price range sold in Australia with sat nav... to name just one feature! (I
therefore think it should have come down in price subsequently as other cars
have marched forwards in features – or, alternatively, the next Prius should be
cheaper.)
Re diesels? Where the same car is available in
both diesel and petrol guises, the diesel always wins on fuel economy – always.
The Mazda 6 is a good example, 5.9 litres/100km for the diesel versus 8.8
litres/100km for the petrol. (But as is nearly always the case, the performance
of the two cars isn’t identical.) And cost? The diesel Mazda 6 is actually
cheaper...
Reality
OK, having dispelled some of the myths, let’s look
at some of the realities.
Firstly, those people who have said that the
length of life of the high voltage batteries in hybrids will prove to be their
Achilles Heel are absolutely right. The Japan-only NHW10 Prius, released in
1998, is now experiencing widespread battery failure. My wife’s car, a grey
market import, has a defective battery. Battery repacking is not available and
even getting secondhand batteries is difficult – a difficulty made, it must be
said, much more so by its grey market status.
Both Toyota and Honda are bending over backwards
to replace high voltage batteries in dealer-sold hybrids – in the US it is
official policy to replace, free of charge, Insight batteries of cars sold in
certain, climatically hot areas. In Australia Honda won’t tell you that you can
have a new battery - but they fitted one to my Insight at no cost.
The next two Prius models – the NHW11 and NHW20 –
have better designed batteries but it is an absolute certainty that these
battery packs will not last the mechanical life of the car. (That’s especially
the case when the Prius mechanicals seem exceptionally durable!) Unless
aftermarket manufacturers take up the challenge to produce OE direct fit
batteries at reasonable prices (and it’s quite likely that in the future they
will), or car manufacturers dramatically drop the price of new batteries, then
hybrids will adopt orphan status as they get old.
People who complain about performance of
economical hybrids and small turbo diesels have usually never driven them. Both
types of cars are usually not overly endowed with power but usually have very
strong bottom-end and mid-range torque curves. Another way of putting this is to
say that they both make lots of power low in the rev and speed ranges.
Drivelines with strong bottom-end performance are
easy and quick to drive in city and suburban conditions, something which most of
us spend most of our time doing.
They do not have high amounts of power necessary
for high-speed hill-climbing or setting good 0-100 km/h times. In both hybrids
and diesels, these deficiencies are easy to remedy – just as with any car, fit a
more powerful drivetrain. However, again just as you’d expect, economy then goes
backwards.
All the passenger car hybrids and turbo diesels
(but not the non-turbo diesels!) I have driven have had quite adequate
power for normal use by a decent driver.
It’s an old chestnut but the actual fuel economy
that is gained from a motor vehicle – conventional, hybrid or diesel – depends a
lot on how it is driven. So there will always be unhappy Prius owners whose fuel
consumption is (comparatively) lousy, there will always be diesel owners who
complain incessantly and there will always be petrol car owners who get
mind-bogglingly good fuel economy.
I can state with absolute certainly that all the
hybrids and diesel passenger cars that I have driven have got excellent fuel
economy, better in every case than a similar size/weight petrol engine car.
I’ve also gained very good economy from
conventional cars – especially Hondas – but even taking that into account,
diesels and hybrids have been better.
Be wary of those people who might be very
economical drivers of conventional cars, comparing their economy figures with
people who drive hybrids or diesels with little understanding of economical
driving....
Conclusion
So which way do I lean – diesel or hybrid? (I
think that conventional petrol engine cars are now right out of the race for
economy and emissions.)
The market diversity is currently too small to
make any such long-term decision viable. There are no commercially available
diesel hybrids. The world’s best-selling hybrid – the Toyota Prius – uses what
can now only be described as an old, low tech petrol engine. (It’s a 10 year old
ex-Echo engine with altered valve timing and a low redline – that’s all.) The
Honda Civic hybrid is hamstrung by the primitive way it mixes electric and
engine power. In the local market, diesels are going backwards – best
exemplified by the Peugeot 405 > 406 > 407 progression, where power and
weight and fuel consumption (and, it must be said, safety) have risen with each
model.
The regenerative braking and engine-off
pure-electric propulsion of a hybrid in city traffic is not only highly
efficient, it’s bewitching. A turbo diesel engine’s torque simply belies its
swept volume – and the diesel is gaining more useful energy from every explosion
of fuel/air mix than a similar size petrol engine.
But on rough roads the Honda Insight rides like a
truck; in strong side winds the Prius wanders like a drunken sailor. The
US-market SUV hybrids look as silly in rationale as putting aerodynamic spoilers
on a military tank. The Audi A6 3-litre diesel has a government test fuel
economy of 8.7 litres/100 – good compared with the petrol opposition but in
itself, nothing special.
On my available budget I have chosen to buy a
Honda Insight – a car that gives better open road fuel economy than any other
that has ever been sold in Australia. I can easily get 3.0 litres/100km on the
open road.
I have also bought a grey market import Prius, one
that I subsequently turbocharged. In my driving it gets about 6.0 litres/100 in
its modified form. However, without a viable high voltage battery, it currently
doesn’t go anywhere.
And now I have a diesel Peugeot. Despite my
comments above, I would have bought a 406 diesel, simply for the better safety
and much more high tech common rail diesel engine. But my budget doesn’t extend
that far and so I have the older 405 turbo diesel. And on my 800 kilometre trip
of the last two days, it got 5.5 litres/100km.
In any other similar size car in my price range,
the economy would have been 30 per cent or so worse. Except of course from a
Prius!
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