Fuel Consumption - How's THAT going ?

[ajay1940]

Last year, We did Melbourne to Sunshine coast return in a Mondeo diesel, averaged 6.3L/100K, which I thought was pretty good.
Just completed the same trip in our new Highline TSI, similarly loaded up, and got 5.6L/100K. I drove the car pretty hard, set the cruise to 5Km over the limit with frequent overtake bursts up to 130.
Needless to say, I won't be buying another diesel.

[brad]

Last year, We did Melbourne to Sunshine coast return in a Mondeo diesel, averaged 6.3L/100K, which I thought was pretty good.
Just completed the same trip in our new Highline TSI, similarly loaded up, and got 5.6L/100K. I drove the car pretty hard, set the cruise to 5Km over the limit with frequent overtake bursts up to 130.
Needless to say, I won't be buying another diesel.

I don't quite get what you are saying - are you so impressed that you intend to keep the highline forever or are you saying that you expected the fuel consumption to be much lower than 5.6L/100km?

If it's a new car then the consumption will continue to improve right through until 40,000-60,000km.

[KWICKS]

Petrol efficiency greater than diesel efficiency was the point.

[adhock]

Petrol efficiency greater than diesel efficiency was the point.

You might want to rethink that view in the light of lighter Golf vs heavier bigger Mondeo. I was getting down round 5l/100km in peak hour congested freeway driving in Perth before the electrics died, and expecting distinctly less than 5l/100km on a long run like yours. That's a diesel Highline wagon.

[ajay1940]

Yes, the point I was making (possibly obscurely), was that the new breed of petrol engines return fuel consumption figures that just about match diesels. Petrol vehicles are also cheaper to buy and service, and to fill up, even using 95 RON. There is also the increasing emphasis on cleaning up the exhaust gases. Diesel Particulate Filters already cause problems, especially for cars doing short trips, and the new Euro 6 requirements may render the diesel engine unviable, in passenger cars.

[Diesel_vert]

The diesel engine will always be more efficient than a comparable petrol engine.

As for the amount of fuel actually consumed for a given journey, that will depend on many external factors. In isolation, it is certainly possible for a diesel engined car to consume more fuel than a petrol engined car.

Comparing a Ford Mondeo 2.0 TDCi with a Volkswagen Golf 1.4 TSI would almost certainly produce fuel consumption results which favour the Golf. Although the diesel engine is more efficient, it is the bigger engine here (2.0 vs 1.4) as well as carrying more mass, so it is inevitable that it will consume more fuel.

Looking at it another way, the displacement of a petrol engine needs to be reduced by 30% in order to better the fuel consumption a diesel engine, such is the efficiency of the diesel combustion process (or the inefficiency of the petrol combustion process)..

It would be fairer to compare the Mk7 Golf 1.4 TSI with a Mk7 Golf 1.6 TDI, but as that particular model is not sold here, we only have the Mk7 Golf 2.0 TDI to compare it with.

[ajay1940]

You make some good points and I have to admit, there's a lot to like about diesel motors, the surge of torque is most welcome when overtaking. But for me, the disadvantages are too many to ignore.

[Diesel_vert]

Fuel efficiency might be interesting to discuss from a conceptual or theoretical viewpoint, but it's fuel consumption and the price of fuel that really matters on the hip pocket.

As efficient as the Mk7 Golf 2.0 TDI may be with its fuel, it is possible to purchase a Mk7 Golf 1.4 TSI for a significantly lower price, due to the way VGA have positioned the Golf model range.

Given the small fuel consumption difference and large price difference between the available petrol and diesel models in our market, it is difficult to justify purchasing the 2.0 TDI based on fuel consumption alone.

It would appear that VGA are treating the 2.0 TDI as some sort of "halo" consumer model in our market, given the price, trim level and the lack of availability of the 1.6 TDI, where choosing the diesel acts as a marker of individuality or a preference for its driving characteristics, rather than for any practical TCO (total cost of ownership) reasons.

I recall reading that sales of TDI models in the previous Golf ranges were not as high as management would have liked (or something to that effect), so this change in market positioning may be a reflection of that, along with a higher focus on the TSI engines this time around.

[Kesh]

I have a rather interesting question for you guys with regards to filling up.

So petrol in my area tends to go from 1.58 down to 1.40, gradually every two weeks, then straight back up to 158 again. Should I fill up a full tank when it's 140, or should I fill up to maybe half a tank every now and then. I ask this because if I fill up when petrol's cheap, I will be lugging around a full tank of petrol, whereas if I do more frequent fills (I live close to a pump), I'd be carrying less weight, but paying more for fuel. What's the better option?

[Diesel_vert]

The density of premium unleaded petrol (95 RON) is approximately 0.75 kg/L, so the difference in mass between a full tank and half a tank on a Mk7 Golf is 19 kg.

Assume a full tank is filled at $1.40/l, while half a tank is filled at $1.49/L (taken as the average of $1.40/L and $1.58/L). That is a price increase of 6.4%.

Therefore, fuel consumption must decrease by 6.4% in order to break even. Whether that will occur from carrying 19 kg less mass, I leave up to you to find out.