Life is full of difficult choices, particularly for parents. Day care? Public or private school? Deep pan or traditional? It doesn't stop. But another major question for many families is: do I choose petrol or diesel for the family car?
In a bid to find out which engine and fuel type really is the best choice, CarAdvice pitted the current Kia Grand Carnival petrol back to back against its diesel twin.
Until the recent arrival of the all-new Honda Odyssey, the Kia Grand Carnival had long been Australia’s best-selling people mover. Set to be replaced in early 2015 by the now Grand-less third-generation Kia Carnival – unveiled earlier this year in New York – the current model is available with two engines, a 3.5-litre six-cylinder petrol and a 2.2-litre four-cylinder turbo-diesel.
Accounting for 85 per cent of Australian Kia Grand Carnival sales, the petrol unit delivers 202kW of power and 336Nm of torque. Making up the difference, the diesel outputs 143kW and 429Nm – down 59kW on its stablemate but up 93Nm.
Starting at $52,290 for the petrol and $56,290 for the diesel, both eight-seat Kia Grand Carnival’s are top-spec Platinum models – which feature electric doors, a power tailgate and leather seats – and power their front wheels via a six-speed automatic transmission.
And while both offer the same 2000kg braked towing capacity, the 71kg-lighter Cherry Cocktail Red diesel claims a sharper combined cycle fuel consumption figure than the 2117kg Crystal Blue petrol – 8.1 litres per 100 kilometres compared with 10.9L/100km, respectively.
So the petrol is cheaper straight off the showroom floor, but in theory the diesel’s superior fuel efficiency should see it eventually make back its $4000 premium. But how long will it take and what are the impacts of other factors such as servicing costs, resale value and depreciation?
Owning a car and living with it everyday is about more than mere facts and figures, however - it’s also about what it’s like to drive. So to compare driveability, and of course collect much-needed data, we’ll be taking both Kias on the same 179km drive loop filled to the brim with their respective fuels.
Combining a 96km highway stretch with an 83km urban leg, our test loop will mix motorway kays with some of Melbourne’s finest stop-start traffic.
Additionally, both cars will be loaded up with the equivalent of five cardboard ‘kids’ (weighing 160kg), have their lights on, automatic climate control units set at 22 degrees, and all four tyres running 40psi. Cruise control will also be locked on whenever safe and able to do so.
On the Road
Heading out to start the highway drive and things in the petrol are, surprisingly, off to an overly enthusiastic start. Seriously punchy off the line, take-off wheel spin is almost unavoidable thanks to an ultra sharp throttle pedal and the petrol’s almost hot-hatch-like enthusiasm.
The diesel is a noticeably more sedate affair, on the other hand, with a far more progressive throttle pedal tied to smoother, albeit slower, acceleration.
Once up to our cruising speed, though, both cars settle in to a steady rhythm of mild steering inputs, the occasional lane change and hovering at or near the 100km/h mark – the tachometer needle sitting at around 1600rpm in the petrol and 1800rpm in the diesel.
Trip One in the books and the first results are in: the petrol managing an average fuel consumption figure of 9.05L/100km, its oil burning twin 7.48L/100km. In terms of average efficiency, the diesel has – expectedly – triumphed, with a difference of 1.57L/100km in its favour.
The dark red diesel Grand Carnival also required 1.51 litres less fuel than its blue petrol-powered comrade and, based on petrol being priced at 1.60c/L and diesel at 1.55c/L, cost $2.77 less to complete the same 96km trip – $13.84 for the petrol, $11.07 the diesel.
A quick refuel and it’s on to tackle the urban crawl...
Stuck in bumper-to-bumper traffic is never fun, but at least sitting at idle in the petrol Grand Carnival at 500rpm things are relatively quiet.
Although perched on an equally comfortable driver’s seat, being behind the wheel of the diesel at its 750rpm idle is noticeably louder – a small cracking of the window alerting you to the even greater diesel din heard by unsuspecting motorists caught alongside.
Again, though, while the petrol’s touchy throttle makes slow motion driving a slightly restless, edgy experience, the diesel’s passive character provides calmer movement.
Hitting 40km/h is met by around 1200rpm in the petrol and a shade under 1500rpm in the diesel.
Trip Two done and dusted, it’s time to once again look at how the two Grand Carnivals fared.
Averaging 11.97L/100km, compared with the diesel’s 8.52L/100km, the petrol used 2.90 litres more fuel than its counterpart and, again based on the day’s fuel prices, cost $4.99 more to complete the identical 83km journey – petrol $16.03, diesel $11.04.
Here too the diesel’s expected fuel efficiency advantage was far more pronounced than for the highway leg, with the average consumption variance being 3.45L/100km.
With notes, fuel receipts and Excel spreadsheets strewn over several desks – as well as one mildly damaged abacus – we have the final results.
Impressively, over our combined 179km test loop, both vehicles recorded an on-test average fuel consumption figure below Kia’s manufacturer claim. The petrol averaged 10.51L/100km (0.39L/100km inside its claimed 10.9L/100km), the diesel 8.00L/100km (0.1L/100km inside its claimed 8.1L/100km).
The total combined cost of Trip One and Two? Petrol $29.87, diesel $22.11. This comes down to an on-test price variance of $7.76 in favour of the diesel.
Extrapolate those figures out to 15,000km – the average annual kilometres travelled by the Australian motorist – and the petrol will end up costing you around $2503 per year, or $650 per annum more than the diesel's $1853.
Standing on its own, this sort of variance would see you make back the diesel’s $4000 premium in a touch over six years.
If, however, we look solely at the recorded highway cycle figures – where the fuel efficiency gap between the two cars was far narrower – the annual variance becomes around $433, blowing the break-even point out to more than nine years.
But if city or urban driving makes up the majority of the ground you are likely to cover in a single year, our test loop figures indicate you would be more than $901 better off, per year, in the diesel rather than in the petrol. Alone, this also drops the break-even point to a much more enticing 4.4 years.
Breaking the numbers down again to come up with a total annual cost figure – based on each vehicle’s on-test combined cycle fuel consumption data and the cost of their respective fuels – and the petrol model will set you back $2522.40 p.a. to the diesel’s $1860.00 p.a. This $662.40 variance equates to a six-year break-even point.
In the real world, though, cost of ownership also includes maintenance, and luckily both cars are covered under Kia’s capped-price servicing scheme, with 15,000km service intervals. Under the scheme, the petrol Grand Carnival will cost you $99 less to service to the end of three years of ownership than the diesel. Interestingly, however, this difference drops to $95 by the end of five years of ownership.
Adding the first year of servicing – $289 for the petrol, $303 for the diesel – to our previous total annual cost figure, and you’re left with the petrol costing $648.40 more than the diesel by the end of the first year – $2811.40 plays $2163.
Now if we average out the total cost for each vehicle over the first three years, factoring in servicing costs along with our on-test combined cycle fuel consumption figures and the cost per litre of fuel purchased on the day, we can come up with a new annual average amount for each car.
This new annual average figure now sees the petrol cost $2857.40 p.a. and the diesel $2228.00, for a revised variance of $629.40 in favour of the diesel. Therefore, based on those average annual cost figures, it would take 6.4 years to break even.
However, if you go one step further again and take into consideration average resale value for each vehicle at the end of three years – around $31,450 for the petrol and $33,950 for the diesel – as well as their equivalent estimated depreciation – about $20,840 and $22,340 respectively – the diesel’s break even point drops significantly to around 3.3 years (largely thanks to the diesel Grand Carnival being expected to retain a higher percentage of its original purchase price compared with the petrol).
Firstly, it’s important to make clear that this test was not ultimately scientifically, nor mathematically, perfect – despite our best efforts. It was intended as a guide to shed light on how big, or small, the often talked about differences between petrol- and diesel-powered vehicles actually are and where they are to be found. Having said that, the test itself was completely real world-based and the results and outcomes have been truly interesting to examine.
Secondly, while the fuel prices on our test day favoured the diesel, in the past it is traditionally this fuel that is often priced above that of regular unleaded.
Also, it’s worth pointing that in the interests of fairness, the test loop drives were completed with the two cars driven side by side, with wheel time in both cars split evenly between myself and CarAdvice’s Lifestyle Editor Tegan Lawson. And with that in mind … an answer. Petrol or diesel?
After clocking up just shy of 360km across both cars, mixing in highway and city miles, my money goes to the petrol. It’s punchy and fun to drive, plus I’d rather be able to spend that $4000 premium straight up, rather than make it back sometime later.
Initially more affordable, and definitely the friskier of the two – particularly when lights change from red to green – the petrol certainly has its strong points. But, for me, I’d take the diesel. It provides a smoother, calmer driving experience than the petrol, will cost you less money each year of ownership than its sibling, and, provided you’re in it for the long haul, the diesel’s higher list price will be made back.